Unesco technical papers
in marine science 49
Pelagic biogeography
Proceedings of an international conference The Netherlands 29 May-5 June 1985
Unesco 1986 UNESCO TECHNICAL PAPERS IN MARINE SCIENCE
Numbers 2, 3, 5, 6, 7, 9, IO. 11, 12, 13, 15, 16, 17, 18. 20,21,22,23,24, 27,28, 29, arc? 30,,ire out of stock. For full titles see inside back cover. Numbers 1, 4, 8 and 14 are incorporated in No. 27.
No. Year SCOR No. Year SCOR WG WG 19 Marine Science Teaching at the University Level. 37 Background papers and supporting data on the Report of the Unesco Workshop on University Pratical Salinity Scale 1978. 1981 WG IO Curricula-/!vai/ah/e in Spanish and Arabic 1974 38 Background papers and supporting data on the 25 Marine science programme for the Red Sea: International Equation of State of Seawater 1980. 1981 WII IO Recommendations of the workshop held in Bremerhaven, FRO, 22-23 October 1974; 39 International Oceanographic Tables, Vol. 3 1981 WG IO sponsored by the Deutsche Forschungsgemcin- schaft and Unesco 1976 •IO International Oceanographic Tables, Vol. 4. (To be published) 1982 WG IO 26 Marine science in the Gulf area-Report of a consultative meeting, Paris, 11-14 November 1975 1976 41 Ocean-Atmosphere Materials exchange (OAMEX) Report of SCOR Working Group 44, 31 Coastal lagoon survey (1976-1978) 1980 — Unesco, Paris, 14-16 November 1979 1982 WG44 32 Coastal lagoon research, present and future, 42 Carbon dioxide sub-group of the joint panel Report and guidelines of a seminar, Duke on oceanographic tables and standards. Report University Marine Laboratory, Beaufort, NC, of a meeting Miami, Florida, 21-23 September 1981 U.S.A. August 1978. (Unesco, IABO). 1981 sponsored by Unesco, ICES, SCOR. IAPSO 1983 33 Coastal lagoori research, present and future. 43 International Symposium on Coastal lagoons Proceedings of a seminar, Duke University, Bordeaux, France, 8-14 September 1981 August 1978, (Unesco, IABO). 1981 — Available in F and S 1982 34 The carbon budget of the oceans. Report of a 44 Algorithms for computation of fundamental meeting, Paris, 12-13 November 1979 1980 WG 62 properties of seawater. Endorsed by Unesco/SCOR/ICES/IAPSO Joint Panel 35 Determination of chlorophyll in seawater. on Oceanographic Tables and Standards Report of intercalibration tests sponsored by and SCOR Working Group 51. 1983 SCOR and carried out by C.J. Lorenzen and S.W. Jeffrey, CSIRO Cronulla, N.S.W., 45 The International System of Units (SI) Australia, September-October 1978 1980 — in Oceanography Report of IAPSO Working Group on Symbols, Units and Nomenclature 36 The practical salinity scale 1978 and in Physical Oceanography. (SUN) 1985 the international equation of state of seawater 1980. Tenth report of the Joint Panel on 46 Opportunities and problems in Oceanographic Tables and Standards, (JPOTS). satellite measurements of the sea Sidney, B.C., Canada, 1-5 September 1980. Report of SCOR Working Group 70 1986 Sponsored by Unesco, ICES, SCOR, IAPSO. Available in At, Ch. F, R, S 1981 WG IO 47 Research on coastal marine systems Report of the third meeting of {npuMtHOHue: 3tot notium (Tetter KnetmtueH) the Unesco/SCOR/IABO 6bn; nepBOHauajibHo tanaii To/ibtco Ha consultative panel on coastal systems aHiTiHAcicoM «bitte non 3aronoBKOM October, 1984 1986 Tenth report of the Joint Panel on Oieanographic Tables and Standards 48 Coastal off-shore ecosystems relationships (JfeorrbiA nolai an 06i>enHHeHHoA rpynnbi no Final Report of SCOR/IABO/ otteaHorpa4>HHecitHM Ta6jitmaH h cTattnapTaM)). Unesco Working Group 65 Hmcctcs Ha arabcKOW, HcnaHCKOM, KHraAcitoM, Texel, Netherlands, September 1983. pyccKOM h 4>paHttyKKOM atbiKax. English only. 1986 Unesco technical papers
in marine science 49
Pelagic biogeography
Proceedings of an international conference The Netherlands 29 May-5 June 1985
Edited by: A. C. Pierrot-Bults S. van der Spoel B. J. Zahuranec R.K. Johnson ICoPB Sponsored by: United Nations Educational, Scientific and Cultural Organization International Association for Biological Oceanography Netherlands Ministry of Education and Science Royal Netherlands Academy of Sciences National Science Foundation, U.S.A. Office of Naval Research, U.S.A. Netherlands Council for Sea Research Amsterdam University Society
40* ANNIVERSAIRE
( '.»«* ÎTIÏÏT »M)
40,h ANNIVERSARY
Unesco 1986 ISSN 0503-4299 Published in 1986 by (he United Nations Educational, Scientific and Cultural Organization, Place de Fontenoy, 75700 Paris. Printed in Unesco's workshops. © Unesco 1986 Printed in France Reproduction authorized, providing thai appropriate mention is made of Unesco Technical Papers in Marine Science and voucher copies are sent to the Division of Marine Sciences. PREFACE
This series, the Unesco Technical Papers in Marine Science, is produced by the Unesco Division of Marine Sciences as a means of informing the scientific community of recent advances in oceanographic research and on recommended research programmes and methods .
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Division of Marine Sciences Unesco Place de Fontenoy 75700 Paris, France. ABSTRACT
The International Conference on Pelagic Biogeography (ICoPB) was held at Noordwijkerhout, Netherlands, from 29 May to 6 June 1985.
The conference was scheduled around nine topics in a combined symposium/ workshop format. It brought together active workers on phytoplankton, zoo plankton, fishes, cetaceans, scientists from a variety of disciplines, ecologists, systematists, historical biogeographers, palaeontologist and physical oceanographers.
The conference recognized a.o. the need:
1. To incorporate modern concepts and theory on biogeography in pelagic oceanography, such as cladistics and vicariance, and to relate modern distribution patterns with patterns and changes read from the fossil record.
2. To develop adequate sampling techniques.
3. To stimulate systematic studies utilizing both traditional and recently developed approaches such as genetic/biochemical methods and studies of living organisms both In situ and in culture.
4. To carry out additional mapping studies, aiso advocating the use of existing collections.
5. To study the congruencies of distribution patterns and to test the hypothesis that closer correspondence between major distribution patterns and large-scale current patterns is related to marked changes in productivity.
This report does not consist of polished and finished research documents. The deliberately short papers are an outpouring of ideas, where we are now and where we ought to be going.
(i) RESUME
La Conférence internationale sur la biogéographie pélagique (ICoPB) 3'est tenue à Noordwijkerhout (Pays-Bas), du 29 mai au 6 juin 1985.
Conçue sous la forme d'un colloque/atelier, cette conférence s'arti culait autour de neuf thèmes. Elle a rassemblé dea chercheurs dont les travaux ont trait au phytoplancton, au zooplancton, aux poissons ou aux cétacés et des scientifiques spécialisés dans diverses disciplines (éco logie, systématique, biogéographie historique, paléontologie e' océano graphie physique).
La Conférence a reconnu en particulier la nécessité :
1. d'intégrer dans l'océanographie pélagique la théorie et les notions modernes de la biogéographie, telles que la cladistique et la vicariance, et d'établir des relations entre les caracté ristiques de la distribution actuelle et les caractéristiques et évolution que l'on peut déduire de l'étude des fossiles ;
2. de mettre au point des techniques d'échantillonnage adéquates ;
3. d’encourager la réalisation d'études systématiques utilisant à la fois les approches traditionnelles et les approches nou velles, telles que les méthodes génétiques/biochimiques, ainsi que l'étude des organismes vivants in situ et en culture j
4. d'entreprendre de nouvelles études de cartographie tout en sti mulant l'exploitation des collections existantes ;
5. d'étudier les concordances dea caractéristiques de la distribu tion et de soumettre à l'épre-‘v. des faits l'hypothèse selon laquelle l'étroite correspondance qui existe entre les grandes caractéristiques de la distribution et celles des courants est liée à des modifications marquées de la productivité.
Le présent rapport ne prétend pas rassembler des documents de recherche soigneusement rédigés et mis au point. Les communications, délibérément courtes, se bornent à énoncer des idées brutes pour tenter de faire le point sur la situation actuelle et sur les objectifs vers lesquels on devrait tendre.
(ü) RESUMEN ANALITICO
Del 29 de mayo al 6 de junto de 1985 se celebró en Noordwijkerhout (Païses Bajos) la Conferencia Internacional de Biogeografîa Pelagica.
En la Conferencia se examinaron nueve temas y el método de trabajo asumiô las formas de un simposio-taller. Participaron en la reunion cientîficos dedicados a la investigaciôn del fitoplancton, el zooplancton, Ios peces y cetâceos, asi como especiallstas de una gran variedad de disciplinas, taies como la ecologîa, el anâlisis sistémico, la biogeograffa historica, la paleontologfa y la oeeano- grarîa fîsica.
La Conferencia seiïalô la necesidad de llevar a cabo las sigulentes tareas.*
1. Incorporar en la oceanografîa pelagica la teoria y Ios conceptos biogeogrâ- ficos mas avanzados -como la nociôn de especies vicariantes- y relacionar Ios modelos modernos de distribuciôn con Ios modelos y cambios estudiados en Ios fôsiles.
2. Crear técnicas adecuadas de muestreo.
3. Estimular la realizacion de estudios sistemâticos basados tanto en Ios enfoques tradicionales como en Ios de reciente elaboraciôn -por ejemplo, Ios métodos genético-bioquîmicos- y de estudios relativos a Ios organismos biológicos in situ y en cultivo.
4. Llevar a cabo estudios cartogrâficos complementarios, fomentando a la vez la utilizaciôn de las colecciones cartogrâficas ya existentes.
5. Estudiar las congruencias de Ios modelos de distribuciôn y poner a prueba la hipôtesis de que la estrecha correspondence entre Ios modelos princi pales de distribuciôn y Ios modelos de las corrientes en gran escala esta relacionada con cambios acentuados de la productlvidad.
En este informe no se recogen documentos de investigaciôn revisados y definiti- vos. En cambio, se presentan textos deliberadamente breves, pero ricos en ideas, sobre el estado actual y la orientaciôn futura que deberfa imprimirse a las actividades en esta esfera.
(iii) PE3I0ME
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IlpeflHaMepeHHo xpaTxne paöOTbi npeflCTaBJinioT coöoft H3Jio»:eHHe Hfleft, o cymecTByximeM b HacTonmee BpeMH nojioiKeHHH n nepcnexTHBax P33BHTHH. (iv) Awa ALA I till I I *"■ I,*^a II aL^oJ ^ ^ ^ ^ LituiI ^ **vJJ ^ * "'^-a II *f • \HÀO / JHi^J-rf 1 «J-*! Jpt / >rf*-« VI i>* I J I — O c AJ.i.% j es P^l L '«Lo JI—9 • AJLo " AJ^JLa-q " (v) « * 1 98 5# 5^2 9 BS6^6 «( ICopb ) ^»»illl9««l#, t '£*T#»WiSNt#. A#L feSsi#wfci»i#AS. «#«, «awi, ^rÉ#fmêmmm. 2. *>*#&*. 3. ) «fî*t «l!(»t«#»S toÉWUMfffBfc „ 4. «ff*#»®!»#*, mmMmtté-fl’&.Mm. 5. mëixt«l 5p±s^#^-§*mwïi «£#£(&«*#* git# t, «&#, -mu, m&mm.x.4-istot®. (vi) FOREWORD In early 1983 Sir Anster Hardy was informed initiatives for ICoPB end to Drs. T. S. S. Reo and 0, about the plans for the International Conference R. Hesle for their stimulating work In the on Pelagic Blogeography -ICoPB. With great scientific committee. Dr. A. C. Pierrot-Bults took enthusiasm he encouraged the organizers and cere of the daily organization of ICoPB and accepted membership of the Comlttee Anster Clavering Hardy was born in Nottingham, with distinction in 1921, when he was appointed on February I Oth 1896. He died on May 22nd Assistant Naturalist at the Fisheries Laboratory 1985 after a long and distinguished career, first in Lowestoft. as a zoologist and marine ecologist. He W8s aiso a His research at Lowestoft, especially that religious thinker and he founded The Religious concerned with food relations during the life Experience Research Unit, Manchester College, history of the herring, supported his selection in Oxford, where he W8s director, and which now 1924 as Chief Zoologist on the first of the Colonial bears his name (The Anster Hardy Research Offices* ‘Discovery" expeditions. This was to Unit). investigate the biology and hydrography relating After school at Oundle he went up to Exeter to the Antarctic whale fisheries. He returned in College, Oxford in 1914. In 1915 he volunteered 1927 with a mass of data and new idees, notably for war service, eventually becoming Assistant on vertical migrations and the exclusion of Camouflage Officer to the 13th Army Corp3 In animals from dense populations of phytoplankton, 1918. Returning to Oxford in 1919 he graduated and on those stimulated by his investigation of plankton patchiness through trials with his Linacre Chair in 1961, he became Director of continuous plankton recorder. These ideas hod to Field Studies, Oxford, for two years. He was aiso a wait, for very soon after his return he was Fellow of Merton College, later en Honorary appointed as the first Professor of Zoology in the Fellow of Exeter College. He was knighted in newly founded University College of Hull. 1957. There, beside ali the work involved in setting up He married, in 1927, Sylvia Lucy, daughter of a new department, he was planning an imaginative Professor Walter Gerstang. She died soon after he research project, based on an improved model of did, but they leave a son and daughter. He was a his continuous plankton recorder. This led in friendly and courteous man, above ali with a keen 1931 to the opening of a joint Department of sense of loyai ity. His eagerness and enthusiasm Zoology and Oceanography at Hull. The aim of the were infectious and he was not afraid to speculate, recorder programme, and Hardy had the charm If there seemed to be supporting evidence. and drive to obtain the grants and colleagues to Moreover, he had admirable gifts as an artist and realise his plans, was to provide regular ( usually a writer. His book Or nt Waters, which is based monthly) charts of the distribution of plankton in on his antarctic journals, gained him a Phi Beta the North Soa and adjacent waters. Such qualities Kappa Award for science as literature in America. and Ingenuity were evident aiso In his use of kites His religious ideas were developed in his Oifford to fly nets, which could be opened and closed like Lectures, which he gave In Aberdeen in 1963-65, plankton nets, Io sample the aerial plankton. The later published es The Living Stream and The recorder programme W8S well under way and Divine Flame. The former was awarded the showed much promise when the war came. Lecomte de Nouy prize at Yale University. Not long in 1940 he was elected Fellow of the Royal before he died he learned that he had been awarded Society, and then in 1942 he was appointed to the the 185,000 dollar Templeton Prize Tor Progress Regius Chair of Natural History at Aberdeen in Religion.’ Thus, his work es a religious Univarsity. In 1945 he was invited by Oxford Investigator continues es well 8s the development University to become Linacre Professor of of his scientific endeavours. Zoology. While he was at Aberdeen and Oxford, and N. B. Marshall after he retired, he continued to take a close interest in the continuous plankton recorder surveys. Actually, on his departure for Aberdeen he was made Honorary Director of Ocean ographical Investigations at Hull and he was aiso editor-in-chief for the first six volumes of the (Hull) Bulletins of Marine Ecology, which was needed to publish their ever expanding records. By 1968, thirty-three merchant ships and weather ships of seven countries provided 120,000 miles of sampling with continuous plankton recorders. More than ever they appreciated that biogeography gave their studies a firm base. During his three professorships Hardy was aiso involved In experimental ecology. For instance, there was his work with Neil Paton on the vertical migration of plankton animals, aiso cut short by the war, and his experiments with Richard Bainbridge (1951 and 1954) using their plankton wheel to measure the rate of ascent and descent of the animals. After he retired from his I8)MÏ2ö1 1 S.van der Spoel. 2 A.CPierrot-Bults. 3 R.S.Schelbema, 4 L .Newman. 5 TAbe. 6 E.Oüartwlg, 7 Tewarii. 8 J. de Visser. 9 NJiarcus. IO J.P.Casanova. 11 JA-McGowan. 12 NBJlarshalI. 13 I.Gotjé. 14 Jl-Reid. 15 AJCleine. 16 I.Sprong 17 A£udc1in. 18 F-Reid. 19 E-Brinton, 20 JX.Wormoth. 21 D.B1asco. 22 Y.Herman. 23 T.L.Hayward 24 El.VenricIc. 25 IO CN ! 8 i? Ui** w .•^2 >333^ io O' 8 j. fc v 2 jr «ï IQ K LL IO (N ® “ ^ _ S 2 SIR DR.O.A. DR. REAR-ADMIRAL Committee Dr. Dr. Dr. Scientific DR. Dr. Dr. Dr. Organising Dr. Dr. Dr. T. Local P. Pafort-van Htlgersom; A. R. AUSTER T. 0. B.J. R. A. S. T. K. S. van C. S. C. R. TOKIOKA REVELLE van K. YERHOEFF S. SKARLATTO Plerrol-Bults Zahurenec Johnson Plerrot-BuHs Hosle Committee: den der Rao HARDY Spoel Spoel P. lersel Committee: J. d'Honneur: Committee: pres H. C. Schalk; KREFFERS ; Ident R. secretory P. Heymen I. Sprong. ; TABLE OF CONTENTS Introduction -A. C. Pierrot-Buits & B. J. Zahurenec I Vertical distribution: stud/ and implications -M. V. Angel 3 Biogeographic boundaries in the open ocean -R. H. Backus 9 Blogeography of the southwestern Atlantic; overview, current problems end perspectives -D. Boltovskoy 14 On the effects of interannual variations in circul ation and temperature upon euphsusiids of the California Current -E. Brintoni J. L. Reid 25 The genetic structure of zooplankton populations -A. Bucklin 35 Similarity of plankton distributionn patterns in two nearly land-locked seas: the Mediterranean and the Red Sea -J. P. Casanova 42 The demographic and evolutionary consequences of planktonic development -H. Caswell 47 Estuaries 8S transitional zones with reference to plankton in the near shore waters -P. Chandra Mohan 51 Latitudinal variation in diversity and biomass in IKMT catches from the western Indian Ocean -D. M. Cohen 54 The role of the Leeuwin Current in the life cycles of several marine creatures -0. Cresswell 60 Life cycle strategies of oceanic dinoflagellates -B. Dale 65 The Azores front: A zoogeographic boundary? -P. A. Domanski 73 The Pleistocene equatorial barrier between the Indian and Pacific Oceans and a likely cause for Wallace's line -A. Fleminger 84 The stomioid fish genus Eustomias and the oceanic species concept -R.H.Oibbs 98 The Oulf of 'Aquaba, a zone of great biological interest -J. E. A Qodeaux 104 Size spectra in mesopelagic fish assemblages -R. L. Haedrich 107 Toward a stud/ of the biogeograph/ of pelagic ctenophores - 0. R. Harbison 112 Problems in open-ocean phytoplankton biogeo graphy -0. R. Hasle 118 Patches, niches and oceanic biogeography -L. R. Heury 126 Variability in production and the role of disturb ance in two pelagic ecosystems -T. L. Hayward 133 Modes, tempos and causes of spéciation in planktonic Foraminifera -Y. Herman 141 On currents off north-west Africa as revealed by fish larvae distribution -H. C. John 149 Polytypy, boundary zones and the place of broadly distributed species in mesopelagic zoogeography -R. K. Johnson 156 Biogeography of the humpbackwhale, Megaptera novaeangliae, in the northern Atlantic -S. K. Katona 166 Ontogenetic vertical migration patterns of pelagic shrimps in the ocean ; some examples -T. Kikuchi AM. Omori 172 Importance of vertical distribution studies in biogeographic understanding: Eastern tropical Pacific vs. North Pacific Central gyre ichthyo- plankton assemblanges -Y.J. Loeb 177 Genetics, life histories, and pelagic biogeography -N. H. Marcus 182 What constitutes an open ocean population -J. Mauchline 186 The biogeography of pelagic ecosystems - J. A. McGowan 191 Biogeography and the oceanic rim: a poorly known zone of ichthyofaunal interaction -N. R. Merrett 201 Monsoon regime in the Indian Ocean and zooplank ton variability -Y. R. Nair 210 Models and prospects of historical biogeography -0. Nelson 214 Transition zones and faunal boundaries in relationship to physical properties of the ocean -D. B. Olsro 219 Distribution of mesobenthopelagic fishes in slope waters and around submarine rises -N. Y. Perin 226 Trophic factors affecting the distribution of slphonophores in the North Atlantic Ocean -P. R. Pugh 230 Zoogeography of the Indian Ocean zooplankton: concepts and constraints -T. S. S, Rao & M. Madhupratrap 235 Vicariance IchthyogBography of the Atlantic Ocean pelagia! -T. S. Rass 237 Epipelagic meroplankton of tropical seas: its role for the biogeography of sublittoral Inverte brate species -R. S. Scheltema 242 Biogeography of oceanic zooplankton -C-t. Shih 250 What Is unique about open-ocean biogeography; zooplankton? -S. van der Spoel 254 Patchiness and the paradox of the plankton -E. L. Venrick 261 Transition zones and salp spéciation -J.de Visser 266 Factors effecting the biogeography of mid to tow latitude euthecosomatous pteropoda -J. H. Wormuth 270 Patterns of phytoplankton abundance and biogeography -C. S. Yentsch & J. C. Oarslde 278 Summary report and recommendations -R. K. Johnson & S. van der Snoei 285 List of participants 292 The International Conference on Pelagic Biogeography logo was designed by Professor S. van der Spoe1 ICoPB 1985 -1- INTRODUCTION A. C. PIERROT-BULTS Institute for Taxonomic Zoology, Amsterdam, the Netherlands B. J. ZAHURANEC Office of Naval Research, Arlington, Ya, U.S.A. "Biogeography cannot confine itself simply to The conference programme was designed around describing the occurrence of living forms, nine topic areas, to be covered in turn by arranging them regionally, investigating the symposium sessions of presented papers, and in ecological causes of distribution. It must aiso workshop discussion sections. The main subjects proceed historically." (Ekm8n, 1953). discussed and reflected in this volume are: Biogeography is commonly defined os the study uniqueness of pelagic biogeography (Brinton & of distribution of organisms on a large scale, Reid p.25 ; Hasle p. 118; Johnson p. 156; McOowan typically on a global scale. Pelagic biogeography p. 191 ; Yan der Spoel p.254), the congruency of deals with these patterns in the pelagic realm of epi-, meso- and bathypelagic patterns and the worlds ocean. The patterns are Influenced by vertical distribution (p.3; Casanova p.42; Cohen ecological and historical processes on many p.54;0odeaux p. 104;Herbison p.112; Kikuchii temporal and spatial scales that are only poorly Omori p. 172; Lœb p. 177; Merrett p.201 ; Parin understood. Thus, more Inclusively, pelagic p. 226 ; Pugh p.230), the role of populations and biogeography is the study of the origin, change and patches (Haury p. 126; Kotona p. 166; Mauchline maintenance of patterns in the distribution of p. 186; Venrick p.26l ), the relevance of genetic pelagic marine organisms in space and time. In studies (Buckiin p.35; Marcus p.182), the role this broad sense pelagic biogeography is the most of life history strategies (Caswell p.47; synthetic field of open-ocean biology. It is aiso, Cresswell p.60; Dale p.65; John p. 149; arguably, the most diffuse, and it is in great need Schel tema p.242), variation and the species of advancing through testable hypotheses, concept (Qibbs p.98; Shih p.250 de Visser rigorous concept and theory. p.266), boundaries aral transition zones (Backus Taking the above into account, the "International p.9; Boltovskoy p.M; Chandramohen p.5l; Conference on Pelagic Biogeography" (ICoPB) in Domanski p.73; Olson p.219; Rao & Madhupratap the Netherlands from 29 May - 6 June 1985 was p. 235 ; Wormuth p.270), vicariance initiated in order to address the status of the field, biogeography and palerceenogrephy (Fleminger t'lghty-five scientists from fifteen nations p.84; Herman p.M I ; Nelson p.2M Rass p.237) (Argentina, Australia, Belgium, Genade, F.R.O., end the role of regional and temporal variability France, India, Israel, Japan, Mexico, the in primary and secondary production (Haedrich Netherlands, Norway, U.K., U.S.A., U.S.S.R.) p. 107; Hayward p. 133; Nalr p 2IO; Yentsch & attended the conference or contributed to these Oarside p.278). proceedings. The participants included active The organizers especially tried to stimulate the open-ocean researchers embracing the broadest incorporation into pelagic biogeography of modern possible diversity of groups and approaches: viewpoints such as: population genetics, aut- ecologists, systematists, workers on phyto ecology, Cladistii, vicariance, plate tectonics and plankton, zooplankton, fishes and cetaceans, paleocirculetion patterns end results from the historical biogeographers, paleontologists, and deep sea drilling programme. physical oceanographers. Specialists who seldom During the first part, the participants if ever directly interact wera brought together. presented their assessment based on their own -2- experienœs and on information from the -publish and distribute papers on pelagic literature. Forty-five papers were presented in biogeography and these symposium sessions. The participants were -participate In activities of a possible SCOR encouraged to mske presentations that would working group. define, address and discuss the outstanding Individuals interested In participating in the questions of open-ocean biogeography in an accomplishment of the alms of the foundation attempt to determine where we are and where we should contact one of the editors of this volume. ought to be going. Consequently, some of the ideas presented were controversial and speculative. This aiso helps account for some of the diversity REFERENCES of the presentations. The papers, of neccessity short, often in abbreviated form, constitute the -BEKLEMISHEV, C. W.. 1969. Ecology and biogeo body of this volume. Since the nine topics are graphy or the open ocean. Publ. House 'Nsuka': more or less overlapping, the papers in this 291pp.(in Russian) volume are presented in alphabetical order. This -CHARNO», H. 8, 6. E. R. DEACON, 1976. Advances in oceanography. Plenum Press, NewYork and volume indicates the goals which may be reached London : 356pp. with new approaches and the neccessity of special -MCGOWAN, J. A., 1972. The nature of oceanic techniques, laboratory and museum facilities and ecosystems. In: C. 6. Miller (ed.) The Biology of management. the oceanic Pacific. Oregon Stale Univ. Press: During the second half of the conference, ali 9-28. participants took part in series of workshops -VAN DER SPOEL, S. 8, R. P. HEYMAN, 1981. A discussing the nine topics, which resulted in nine comparative alias or zooplankton. Biological working group reports. These have been condensed patterns in the ocean. Bunge sclent. Puhi. and are edited as the Summary Report and Utrecht: 186pp. Recommendations, General Conclusions and -VAN DER SPOEL, S. 6, A. C. PIERROT-BULTS, 1979. Specific Recommendations. Zoogeography and diversity of plankton. This volume compiled by selected scientists Bunge sclent. Puhi. Utrecht: 410pp. tries to mark the pathway for pelagic biogeo- grephy in the neer future. During the last decade a number of publications adequately pictured the present stage of the field (Beklemishev, 1969 ; McGowan, 1972; Char nock & Deacon, 1978; Van dar Spoel & Plerrot-Bults, 1979; Yan der Spoel & Heyman, 1981). Discussions should now focus on the question what to do in the future. We hope some of these questions will be answered by this volume. One of the first results of the Conference was the establishment of a non-profit foundation in the Netherlands entitled "Stichting International Conferences on Pelagic Biogeography (ICoPB)". The alms of this foundation are to: -organize an International Conference on Pelagic Biogeography in 1990 and afterwards -execute activities in the field of pelagic biogeography Including work towards the publication of this proceedings volume. -maintain and expand contact between Interested parties and institutions in the field -3- VERTICAL DISTRIBUTION : STUDY AND IMPLICATIONS M.V. ANGEL Institute of Oceanographic Sciences, United Kingdom INTRODUCTION of the integration of ali the individual hypervolumes for each species's total population The oceanic water column Is characterised by and its interaction with historical events. A vertical gradients in environmental character species may not occupy the whole of its potential istics, some of which are highly correlated, range because in the pest it has been inhibited in whereas others are more or less Independent. The its spread; for example, species endemic to the abiotic properties include a wide range of Southern Ocean may be capable of living in Arctic physico-chemical characteristics, some un waters. affected by biological processes (e.g. temperature, Every individual organism needs to achieve four hydrostatic pressure, density, water column basic objectives in order to be biologically stability and solubility compensation depths), but successful: I ) it mu3t breed, and hence 2) it must others are influenced to some extent by biological be able to find enough food; 3) survive in the face processes (e.g. light intensity and colour balance, of predation pressure; end A) live within its dissolved oxygen, nutrient and certain trace energetic resources. The optimum conditions for element concentrations, dissolved organic con one objective may differ quite markedly from centrations, particulate size spectra 8nd fluxes). those for another. This leek of compatibility is Many abiotic properties have a major influence on evident In the water column, in which a species tile biotic characteristics such as primary may find optimum feeding conditions in the prediction, standing crops, turn-over rates, food near-surface layers, whereas predation pressure availability, predation pressure, micro-organism may be much reduced deeper down, where aiso the activity, morphological and physiological adapt cooler water temperatures may result in meta ations, particulate production and recycling, bolic processes being more efficient (Iwasa, species richness and diversity. Those biological 1983). Natural selection can be expected to have properties which are under most direct physical resulted in each species evolving a near unique control can be fairly well modelled, and hence example In the spectrum of solutions to the their profiles predicted with a reasonable degree problem of balancing the trade-offs; competition of accuracy, given an adequate physical data set, occurring where two sympatric species have e.g. primary production (Platt, Mann & arrived at similar solutions. These solutions, in Ulenowicz, 1981). But, whereas the gross essence, underlie ali autecological studies patterns can be predicted, the detailed relation involving aspects of life-histories (e.g. onto ships between species composition end between genetic migrations and diapause), morphological small scale spatial phenomena remain unresolved. and biochemical adaptations (e.g. patterns of coloration and types of bioluminescence) end behavioural characteristics (e.g. diel vertical DISCUSSION migrations). Any particular species may have a critical stage Each species is faced with a multi-dimensional in its life history at which the limits for its matrix of gradients within which it has Io find lis survival are more restricted than at others. These niche. Each individual lives within a hypervolume limits will then define the core of its distribution; limited by the conditions for survival which may the periphery of this core-ranga will be extended shift during its life cycle, but in many cases there by diffusion and advectlon in p8S3ive species and is a mora restricted hypervolume within which it by migrations in more mobile species. can successfully breed. Biogeography is the study Long-term climatic variations in water -4- structure may have left persistant Imprints on experimental studies are needed to establish the the pattern of species distributions and causal factor. In the latter case identification of community structura. The CLIMAP programme correlations between biotic and abiotic factors in (Cline & Hayes, 1976) illustrated just how vertical distribution patterns will provide dramatic the changes have been in the North guidelines for designing the experimental stategy. Atlantic pelagic communities since the peek of the As the numbers and geographical coverage of last glaciations, relative to the North Pacific comprehensive vertical studies Increase, they are where the effect seems to have been restricted to beginning to provide considerable insights into the longitudinal shifts In the blogeographlc zones, in understanding of horizontal distribution patterns, the long term, the pattern of continental drift and particularly If the data are properly archived the opening and closing of deep channels have been (e.g Domanski, 1981). Thus two species which major influences in determining inter-oceenic are sympatric in a horizontal sense, may prove to distributions, and the maintenance of these be allopatric in a vertical sense. In addition where patterns Is related to the vertical ranges of the two similar species overlap in their horizontal species. For example the opening of the deep ranges, character displacement may lead to their channel between Australasia and Antarctica vertical segregation, at leest at certain stages of which was followed by a general cooling of the their life cycles (e.g. Angel, 1982). Full vertical deep waters (Shackleton, 1982), has resulted in coverage of the water column can reveal anomal the progressively greater segregation of warm- ous geographica! patterns which need explanation. weter species whereas the deep cold water fauna An example is seen in the halocyprid ostracod has probably become steadily more pan-oceanic. Halocypria globosa which off Bermuda The vertical gradients in environment para dominates the neer-surface layers although adult meters can lead to the evolution of physiological, males only occur at deep mesopelagic depths morphological and behavioural adaptations which (Deevey, 1968; Angel, 1979). In the N.E. increase an organism’s chance of survival within Atlantic it has not been taken pelagica! ly north of a restricted depth range yet reduce its fitness 40*N despite quite extensive geographical cover beyond that range. Shifts In the vertical profile of age, but a series of benthopelagic samples taken e limiting parameter will bring a parallel shift within IO-100m of the see-bed on the con in the species's vertical ranga; unless this tinental slope at depths of 1000-1600m to the vertical shift results in another factor becoming south of the Porcupine Seabight (around 49*N limiting, in which case a boundary to its 13*W) contained large numbers of adults (Ellis, horizontal range will occur. An example of such pers. comm.). Assuming the Bermudan and adaptations is provided by the mirror-sides of Seabight specimens ere conspecific, questions many mesopelagic fishes. These appear to provide arise as to whether the letter are either an effective camouflage within the depth range, expatriates possibly carried northwards in the limited at the shallow end by the depth et which flow of Gulf of Gibraltar water, or If the the light field becomes totally symmetrical in a distributions ara distinct or not. vertical sense, and at the deep end by the depth at Comprehensive knowledge on vertical distrib which bioluminescent emissions become utions at ali stages of the lifecycle is essential to significantly bright relative to in situ daylight understanding how the faunas of Mediterranean intensity (Denton, 1970). Such morphological type seas originate and are maintained (e.g adaptations often become progressively expressed Alcaraz, 1977; Furnesti, 1979; Vives et al., during larval development and are associated with 1975; Weikert, 1982). For example the ontogenetic migrations (e.g. Badcock &Larcombe, occurrence of some of the glacial relict species In 1980). Such adaptations which have morphol the Mediterranean (e.g. Meganyctiphanes ogical or anatomical expressions are accessible to norvegica and Benthosema glaciala can bo study through sampling strategies designed to understood by extrapolating present distributions study vertical distribution, but where the to the conditions shown to have occurred 15,000 adaptation is physiological or behavioural BP by the CLIMAP programme (Cline & Hayes, -5- 1976). These Méditerranéen populations ms/ biogeographic boundary. have become reproductive!/ isolated from the The clearest signal is probably generated at the other stocks now found in boreal waters and in the subtropical convergences, where permanent N.W. African upwelling region, through their stratification and persistently high near-surface adaptation to the warm deep water of the stability of the water column occur on the Mediterranean. Then if either climatic conditions low- latitude side, and there is a seasonal cycle of were to fluctuate again so that the populations stratification and water column stability would become sympetric, or shifts in the larval (Robinson, Bauer tk Schroeder 1979), and hence ecology should occur which could then allow the primary production, on the high latitude side. passage of stocks into or out of the Mediterranean Associated with these changes, which produce via the currents systems In the Straits of sharp shifts in the degree of seasonal pulsing of Gibraltar (Gascard& Richei, 1985), the sibling production, are major quantitative and qualitative stocks would become sympatric but fail to shifts in the structure and function of the pelagic interbreed; such a mechanism may help to explain ecosystems. This Influence probably extends, the high species richness of pelagic communities. albeit attenuated, right down to the see bed. Some Apart from the land masses, the main potential idee of the speed at which signals of events at the barriers to geographical ranges are oceanic fronts sea surface can be transmitted down through the at which there are major changes in the water column and hence the degree to which the physico-chemical and biological structure of the boundary effect may be blurred or displaced by water column. Too little attention has been paid to diffusion and advection, Is given by the recent the role of fronts in determining distribution results from sediment traps (e.g. Deuser, Ross& patterns at ali scales of interaction (e.g. the Anderson, 1981) and time-lapse cameras influence of mesoscale features, see Angel & deployed on the soa floor ( Billett, Lampltt, Rice & Fasham, 1983). So long as the conditions do not Mantoura, 1983). Even so, there are species become lethal across a front, the length of the which are sufficiently adaptable to cross the organism's generation time relative to the boundary by adjustment of their vertical range persistence and the predictability of a front will (by submergence) while others are not (Fig. 1 ). determine whether its response is by population Deeper-living species seem able to cross such growth or behavioural. Wiebe and Boyd's (1978) boundaries more readily than the shallower- observations on Nematoscelis megalops living. However, this may be simply because illustrate how a species's vertical rangB may deeper - living species tend to have more extensive gradually shift within a decaying ring, so that it depth ranges, and merely have to restrict their persists only as an expatriate non-breeding range to be able to cross the frontal zone. population. However, the degree of change in physical characteristics across a front may determine its influence on the community CONCLUSION structure. For example preliminary date from a front to the south-west of the Azores (Gould, Detailed vertical distribution studies are not only 1985; Fasham, Platt, Irwin & Jones, 1985) useful in trying to understand biogeographic show that although the specific composition of the distributions, but are essential to explain many pelagic community changes very little (Pugh, aspects of these patterns and to give pointers to 1975; Angel, 1979), there were major changes their mode of development. in the pattern of dominance and in the vertical structuring of the community biomass (Angel, 1985). In this example the physico-chemical REFERENCES changes across the front must hewa been too minor to limit the ranges of the vast majority of species -ALCARAZ, M., 1977. Claóoctros y Ostracoda da loi examined. This raises the question as to how alradadoras del Estrtcho do Gibraltar an junlo-Jullo da well-defined a front has to be to become a major 1972. Nes. £xp. Clini. Cornfde, 6 : 41-63. -6- A Conchoecia obtusata c . . ° ■ 8000 . . 0 . 1000 0 30 0 30 0 30 n T...... V B C.hyalophyllum 0» ■ ■ . 'Q00 . . ■ ■ ■ ■ "3°° . . ■ l0.00 l! C C.imbricata _i_I I—J_ 1000- Qv t—5* 1 Yo I I* 2000 J -7- -AN6EL, 11. V.. 1979. Studies on Atlantic halocyprid -FASHAM, M. J. R.. T. PLATT. B. IRWIN & K. JONES. ostracods: their vertical distributions and community 1985. Factors affecting the spatial pattern of deep structure In the central gyre region along latitude chlorophyll maximum in the region of the Azores 30*N from off Africa to Bermuda. Prog. Front. Prog. Oceanogr., M: 129-165. Oceanogr., 8: 3-124. -FURNESTIN, M.-t., 1979. Aspects of the -ANGEL. M. V.. 1962. Halocypris inflata (Dana, zoogeography of the Mediterranean plankton. In: S. 1849) and H. pelagica Claus, 1890; sibling species van der Spoel 8» A. C. Pierrot-Bults (eds). which possibly show character displacement. In: R. H. Zoogeography and Diversity in Plankton. Bate, E. Robinson & L. M. Sheppard (eds). Fossii and Bunge scient. Puhi., Utrecht : 191-253. Recant Ostracods. Ellis Horwood/British Micro- -GASCARD. J. C. & C. RICHEZ, 1985. Water masses palaeont. Soc. Chichester: 327-343. and circulation in the western Alboran Sea and In the -ANGEL. M. V.. 1985. Vertical migrations in the Straits of Gibraltar. Prog. Oceanogr., IS : oceanic realm; possible causes and probable effects. 157-216. Conir. mar. Sei., 27. Suppt. -GOULD, W. J., 1985. Physical oceanography of the -ANGEL. M. V. & M. J. R. FASHAM. 1983 . Eddies and Azores front. Prog. Oceanogr., M. 167-190. biological processes. Chapter 22 In; A. R. Robinson -IWASA. Y., 1982. Vertical migration of zooplankton: (ed.) Eddies in Narine Science. Springer-Verlag, A game between predator and prey. Am. Nat., 120 Berlin : 492-524. : 171-180. -BADCOCK. d. 8, R. A. LARCOMBE. I960. The -OWEN, R. W. M., 1981. Fronts and eddies in the soa: sequence of photophore development in Xeno Mechanisms, interactions and biological effects. In: A. dermichthys copei (Pisces: Alepocephalidae). Fig. 1 Vertical distributions of four species of planktonic ostracods at six stations approximately along 20*W, with day profiles to the left and night profiles to the right. A). Conchoecia obtusata a northern species showing only slight evidence of submergence; B). C. hyalophyllum a species associated with North Atlantic Central Water which shows changes in Its die! vertical migration behaviour with latitude; C). C. imbricata another species associated with NACW and showing even greeter changes in its intensity of dial migration; D). C. boreal is a northern species showing clear evidence of submergence. Note the abundance scales vary between profiles. -e- Prog. Sérias, 8\ 129-143. -WIEBE. P. H. B. S. H. BOYD. 197B. Limits or Nematoscelis megalops in the North-western Atlantic In relation to Gulf Stream core rings. II. Horizontal and vertical distributions. J. mar. Res., 36 : 119-142. -9- BIOGEOGRAPHIC BOUNDARIES IN THE OPEN OCEAN RICHARD H. BACKUS Woods Hole Océanographie Institution, U.S.A. INTRODUCTION physical basis of the distribution in water-mass and circulational terms (Fig. 1), end extra It Is assumed that the distribution of plants and polation of the organism's occurrence from the animals In the pelagia! Is directly related to the sampled to the unsampled parts of a physically physical properties of the ocean or indirectly to homogeneous body of water is a reasonable them through so-called biotic factors: the effects procedure in tentatively describing its range of species upon one another. Thus, biogeographic when such a description is needed. boundaries are taken to be actual physical The sudden appearance, disappearance, or boundaries such as lie between water masses and radical change in abundance of an abundant their subdivisions; I mean the term “water mass" organism in collections made along a transect to be interpreted in a very general we/. The search for the factor (or the few factors) that explains the distribution of a species or narrow group of species of pelagic plants or animals has rarely, if ever, been succesful. Surely it is a complex of factors that exerts the control, the whole suite of properties that o Lepidophanes gaussi column of water possesses acting in concért, the individual elements being scarcely separable from one another. BIOGEOGRAPHIC REGIONS What we really care about knowing is why a certain species is distributed in the way that it is, or conversely, why a certain homogeneous part of the ocean supports the complex of plants and animals that it does. The simple description of the ranga of this or that plant or animal, a necessary SPICIMENS/MOUR preliminary in which many of us engage, is of •4- V limited interest in itself. One rarely has adequate biological collections for describing the range of a pelagic organism well on the basis of those collections alone. But if the ranges of organisms are controlled by physical factors, then physical description of the ocean (which is more extensive than biological Fig. 1 Distribution of the myctophi fish description) can be enlisted in the service of Lepidophanes gaussi, an inhabitant of the biogeography. The distribution map of an abundant subtropical seas of the Atlantic. The diameter of species (Abundant species ere the species from the filled circles Is proportional to catch rate. which we bast learn), is often suggestive of the Re-drafted from Backus et al. ( 1977). -10- indicates a boundary, biogeographic and physical, carefully taking into account ali the imperfections and its basis in physical terms often can be of the data. Only when the framework cannot assigned. By such procedures physical boundaries accomodate a set of data compared in this way that are aiso biogeographic boundaries have been should the framework be elaborated. Such a identified and from these physical boundaries a framework is presented for the world ocean as b general framework for pelagic plant and animal map (Fig. 2) and es a diagram (Fig. 3). It is distribution can be constructed. purposely kept very simple for the time being. It cannot be expected that a biogeographic In figure 3 solid lines represent the boundaries boundary in the open ocean will be very sharp. of biogeographic regions; broken lines divide Not only are the physical boundaries upon which regions into provinces. Few of the latter have been the biogeographic ones depend not very sharp, but attempted and, for the moment, definitions are not aiso a spectrum of responses to a physical given for "region" and "province” save to say that boundary by organisms would be expected even the latter is a subdivision of the former. North is were the physical boundary sharp. Nevertheless, at the top of the diagram. Beginning there, the it is convenient when speaking of plant and animal diagram is divided latitudinally into nine regions : distribution to think of a boundary as a line and Arctic, Subarctic, northern Temperate (or not to speak of a boundary es an area within which northern Transitional), northern Subtropical an organism can range. (An indivisible area is (or northern Central), Tropical, southern delimited by boundaries; it does not contain Subtropical (or southern Central), southern boundaries; and the range of an organism cannot Temperate (or southern Transitional), Sub- be said to be boundary-less). antarctic, and Antarctic. An Arctic region might be It is my belief that the tentative patterns of omitted, as the Arctic Ocean appears not to have a distribution for pelagic organisms have been regular pelagic biota. The term "Transitional" proliferated too much. Often this canes from should be abandoned as It Is both ambiguous and taking too seriously differences in distribution insufficiently descriptive. I feei particularly whose origin actually lies in the imperfection of uncertain about arrangements at the southern end the data. This is an especial hazard when one uses, of the diagram. not his own dete, but the published data of others. The only latitudinal division of the biogeo The absence of a species in an expected place is graphic regions into provinces is the division of sometimes merely the want of the right sort of the northern and southern Subtropical regions collecting effort there. The presence of a species into poleward and equatorward halves. These in an unexpected place is sometimes merely the provincial boundaries, which In some oceans have result of a few expatriate specimens (waifs) that been called Subtropical fronts (Roden, 1975), would have been disregarded had the dete set that divide the westwind part of each of these regions was used expressed relative abundance. There are from the tradewind part of each. The Subtropical many other sources of difficulty including mis- front in the North Atlantic often has been called identification and taxonomic confusion and some the "northern Subtropical Convergence" ( "nord- not so simple as these. liche subtropische Konvergenz", Wüst, 1928), I believe that there may be general enough but It is not the homolog of the subtropical agreement about the bold outlines of plant and convergence of the southern hemisphere, which is animal distribution in the pelagia! so that there the regional boundary between the southern can be erected a fairly simple framework to which Subtropical and southern Temperate regions individual plant aoi animal distributions can be (Yeronls, 1973). rigorously compared. By “rigorously" I mean The biogeogrephic regions can be divided Fig. 2 liep of biogeogrephic regions of the world ocean. The boundaries drawn are approximate. 1 - arctic, 2 - subarctic, 3 - northern temperate, 4 - northern subtropical, 5 - tropical, 6 - southern subtropical, 7 - southern temperate, 8 - subantarctic, 9 - antarctic. Is -12- rAMM' Ali ANTIC INDIAN BIOGEOGRAPHIC PATTERNS Ainu ? 1 1 Suture nr 1 1 It is obvious that the units of geographic 1 1 Northern temperate 1 ! distribution ( regions and provinces) are not to be 1I -1 -j Subtropical icn»«rgenc* "> Northern Subtropical Subtropica! front equated with ranges or distribution patterns. —I— (When a range is occupied by two or more species 1I 1I 1 If epic 1 1! 1 of plants or animals, it can be called a pattern.) ---- 1---- 1 ---- [ i Rather, the regions and provinces are elements SjMrcpu •’ - -t— —f- Subtropica! froM J - -4— Suttrcpu it « rr »«r gfive t from which, by their varied occupancy by species 1 1 —t— '•.'ulli BIOGEOGRAPHY OF THE SOUTHWESTERN ATLANTIC; OVERVIEW, CURRENT PROBLEMS ANO PROSPECTS DEMETRIO BOLTOVSKOY University of Buenos Aires end Coni cat, Argentina. INTRODUCTION assemblages. But the draft proposed over 40 yeers ago did not undergo radical changes. On the other The Soutwestern Atlantic ( SWA) is one of the least hand, figures 3 and 4 show that, as far as the studied areas of the world Ocean (see D. locations of the boundaries are concerned, the Boltovskoy, 1979). Therefore, much bæic agreement is rather poor, and this lack of descriptive work is needed before this area can be coincidence does not seem to decrease with subject of more or less ample and comprehensive successive studies (Fig. 3). biogeographic studies. However, a retrospective These biogeogrephic patterns are similar inas glance at the advances over the past decades and much they ali distinguish warm-water from cold- comparison with the results achieved elsewhere water assemblages, and several further divide can yield some reflections on the implications of each of these into two sectors. The limits between the methods used, the aims of the investigations areas, however, very widely (Figs. 3 & 4). performed, and the biogeogrephic significance of Furthermore, the Transition is absent from over the results achieved. The review and discussions half of these schemes. that follow are based on an ecological prospective inasmuch the divisions analyzed are assumed to separate discrete communities or ecosystems. SPECIES’ DISTRIBUTION PATTERNS, WATER Figure IA outlines the general hydrological MASSES ANO BIOGEOGRAPHY setting of the area. Figure IC illustrates the water messes present in the area es recognized by In oceanography, biological indicators have been distinctive TS curves (Fig. IB). A review of the used in two different ways: as tracers of water biological features of the SWA is given by D. movements, and as sensors of oceanographic para Boltovskoy (1978,1981). meters. The difference between these two applications is subtle, sometimes they are closely Interwoven or even overlapping. E. Boltovskoy OVERVIEW OF THE BIOGEOGRAPHIC MODELS (1967) concluded that, among other require PROPOSED FOR THE SOUTHWESTERN ATLANTIC ments, an adequate tracer should be fairly - but not extremely - sensitive to ecological para One of the first blogeographic charts of the oceans meters: it should be sensitive enough riot to which included the SWA, based on zooplankton, inhabit more than one of the currents or water was published by Meisenheimer in 1905 (Fig. masses that ara under study in a particular area, 2A). Steuer modified Meisenheimeri pattern but not es sensitive as to disappear from its (Fig. 2B). The chart published by Henschei 15 habitat es soon as environmental conditions change years later ( 1938; 1942) already included ali slightly. the areas that are usually distinguished today The "biological tracer method" has been used (Fig. 2C). regularly for biogeogrephic purposes, thus Subsequent studies, both biological and assuming tacitly that the end of a given current physico-chemical, contributed to describe the (that Is, of its tracers) is coincident with a boundaries and assess their seasonal displace blogeographic boundary. However, this may or ments, and further characterize the main zones by may' not happen, end the underlying assumptions their abiotic parameters and typical biological can be valid in sona areas, but not in others. The -15- 70* 50’ 30* W 70 50* 30*W Fig. 1 Currents (A) and water masses (C) with their corresponding typica] TS curves (B) in the Southwestern Atlantic. BC : Brazil Current; CCE : cold-core eddies; CHC : Cape Horn Current; EWD : East Wind Drift; 0C : Guiana Current; FO : Malvinas (=Fa1k1and) Current; PCC : Patagonian Costai Current; SACO : South Atlantic Central Gyre; SEC : South Equatorial Current; WCE : warm-core eddies; WWD : West Wind Drift. (A: compiled from different sources; B &C: from Gorshkov, ed., 1977). criterion of the goodness of a tracer is usually sensors has to be relatively narrow; their derived from hydrological patterns established on distribution should match a more or less the basis of physical studies. In other words, an homogeneous TS envelope, rather than a current organism is considered a good tracer if its which can undergo wide temperature and salinity distributional range matches adequately the known changes along its route. or suspected course of a current, and it still In addition to water mess-related conclusions, survives in its waters when these are no longer work with tracers and sensors interleaves distinguishable by their physical parameters. intimately with biogeography. Thus, Indicator Thus, its distribution indicates the influence of a species initially selected for their fidelity to a current, the extension of a physical phenomenon, current or to certain temperature and salinity but not necessarily a major biological break (Fig. ranges end up being the main material for defining 5). biogeogrephic 8rees. This happens so frequently On the other hand, the species that are snugly and to such an extent that it often io difficult to restricted to a single water mass are considered discern whether a particular report is dealing biological indicators (=sensors) of the latter. As with water messes or with biogeogrephic areas. opposed to trocers, the environmental tolerance of In many of the Investigations which include ali -16- -17- or most of the species belonging to one or more higher level taxa (ss opposed to those that deal with indicators only), a major point is made of analyzing closely the relationship between water masses and planktonic distributions. Thus, individual species' ranges arc examined "from a water mass point of view" arid the conclusion Is commonly reached that water masses account for the general patterns adequately. A tacit, and sometimes explicit, Implication of these results is that since most species show clear affinities for given water masses, ergo their distribution boundaries match water mass limits. There are many examples to support this assumption. However, a closer look at this relationship shows that, although there is an Fig. 3 Approximate limits of distinctive faunal evident tendency for the species' boundary lines planktonic assemblages in the Southwestern to be denser 8t the water mass limits, most of Atlantic (pelagic waters). 1 : Foraminifera (E. them fall actually within water masses, rather Boltovskoy, 1970a; 198la,b); 2 : Tintinnina than on boundaries between them (e.g., planktonic (Souto, 1981 ); 3 : Siphonophorae (Alvarino, Foraminifera in the SWA, cf. F. Boltovskcry, 1981); 4 : Hydromedusae (Rsmirez & Zamponi, 1981b, Fig. 163; Euphausiaceae in the Pacific, 1981; based on Kramp, 1957); 5 : Pteropoda cf. Brlnton, 1962, Fig. 101). Figure 6 suggests (Van der Spoel & Boltovskoy, 1981); 6 : that these mismatches are especially obvious Ostracoda (Angel, 1981); 7 : Copepoda when detailed charts (rather than schematic (Bjornberg, 1981); Euphausiacea (Antezana & simplifications) are available. Brinton, 1981). NS : limits between zones not Figure 7 shows that, when total ranges are specified. compared, the great majority of the species are not found in ali sectors of the water mass thai they boundaries regularly, but that plankters evidence inhabit, very few extend throughout an entire a clear tendency to Inhabit more than one water water mass, and even fewer are effectively mass. Table I shows an example of the distribution restricted to a water mass. There are some of the species of some taxa between the endemics (especially in the Subarctic area), but cosmopolitan, moderately broad and endemic types practically none is an endemic and is found (see aiso Venrick, 1971; Reid et al., 1978; Yan throughout the entire water mass. Soest, 1979). Reviews of the information available suggest not In the light of these considerations, table II and only that most species cross water mass figure 8 summarize the distribution types of Fig. 2 Major biogeographic zonations of the southwestern Atlantic Ocean according to different authors. Zones: A= Antarctic; AC= Argentine coastal; Ar= Argentine; B= Brazilian; CT= circumtropical; E= Equatorial; 1= intermediate; N= notalian; No= northern limit; S= Southamerican; SA= Subantarclic; SAb= Subantarctic boundary; SAN= Subantarctic neritic; SA0= Subantarctlc oceanic; So= southern limit; ST= Subtropical; STN» Subtropical neritic; STb- Subtropical boundary; STO» Subtropical oceanic; T= Tropical; TE= Temperate; TN= Tropical neritic; TO= Tropical oceanic; TR= Transitional; TRN= Translrlonal neritic; TR0= Transitional oceanic; WT = western Tropical. Sources: A= Meisenheimer ( 1905); B= Steuer ( 1933); C= Henschei ( 1938); 0= Boltovskoy ( 1959); E= Bogdanov (1961); F= McIntyre & Bé (1967); 0= Nesis ( 1974); H= Pierrot=Bults & Yan der Spoel (1979); 1= Dadon & Boltovskoy ( 1982). -15- 70* 50* 30* W IKTDfiCHOOICAl INOiCAIOftS I luttas I SIN SOA S eilrexetyr»irfy. tui scnvtlvt Ml OOter requtrenenls liui ilgrillDni | Assaaed basic ranga, I Augaetf futility le e jim eipctrialuwivente and ran^ jteriti jI Beter»xt ef uvirenaentil (ia prxlica, ■pore- I/S I envelope) I Ilteraoadcr», Mlinoaeters 0°oA Fig 5 Summary of the basic differences between hydrological tracers and sensors. BIOGEOGRAPHIC ZONATIONS, TRANSITION ZONES AND COMMUNITIES Starting in the 1950' s, analyses of the vast Fig. 4 Composite sketch of the biogeographic information accumulated on the distribution of boundaries illustrated in Fig. 2C-I. oceanic plankton showed that recurrent biological assemblages are linked to specific segments of the ranges of variation of some parameters other than oceanic plankters in terms of water masses and temperature and salinity. Among these are their boundaries. The fidelity concept is that of phytoplanktonlc primary production, zoo- Boltovskoy, 1967 (as referred to water mas3 planktonic standing stock, vertical stratification Indicators), and of Fager, 1963 (as referred to and migration patterns, endemism, equitabllity, communities), with the additional restriction that particle size, food web charecteristcs, seasonal the species must effectively occupy ali the area production variations, metabolism, turnover rate concerned. Fager' s (1963) "vitality" and (Ylnogradov, 1968; Koblentz-MIshke et al., "periodicity" criteria are, in this context, two 1970; Bogorov, 1974; McGowan, 1971; 1974; aspects of the abundance concept. Conover, 1979; etc.). These distinctive functional The results reported ( see reviews in Johnson & features gave grounds for concluding that the BrInton, 1963; Beklemishev, 1969; McGowan, assemblages In question are fairly Independent 1971), achieved after the analysis of thousands of ecological units: communities or ecosystems. samples loeve little doubt that there effectively Is Co-occurrence is a necessary, but not a strong affinity of most of the species treated for sufficient, requirement for the community specific areas of the ocean. However, their concept. The co-occurring organisms must be aiso Individual sensitivity to the boundaries functionally interrelated. A cutoff value can be established by means of physical studies is fair at given by the condition that relationships within a best. community are closer than those with members of -19- Table I Approximate numbers of species of some zooplanktonic groups present in the surface waters of the southwestern Atlantic (modified from Boltovskoy. 1970). Antarctic Subantarctic Subtropical* Cosmopolitan b Tropical (at laist Subant. Total and Subtropical) *PP P R P R P R Z Foraminifera S 0 12 2 30 IO 2 33 Pteropoda** 3 - 9 2 50 46 4 62 Citae tngaatba 6 0 11 2 20 12 7*»» 26 Salpidae 3 2 S 2 17 IS 2 20 Appendicularia 23 7 14 0 30 14 14 35 Totals 40 9 SI 0 147 97 29 178 X of tatei io SWA 22 5 29 . 4 83 — 16 — “Almost ali these species inhabit both areas * * Subspecies, formae and morphae computed separately * “ “ Ali maso and bathypelagic at mid and low latitudes P= present; R= restricted (endemic) Table II Some attributes of the distribution types of planktonic organisms illustrated in figure 8. Fidelity to Fitness os indicator of Distributa typa Frequency in in figura 8 plankton 8 C 8 c B/C limit 1 + - 4 - 4 - 2 - 4 - -(♦> -<♦> - 3 - - - -(♦) - - 4 - - - - 4 - S “ - -<♦> - 4L 7 - -- - -(♦> 44 8 - - - - - 44 9 - - - -<♦> ♦(?) IO - - - - -<♦> 4 “ 11 " " “ -(+): Not adequate, but can be used -20- -21- NORTH 100—1 1 Euphausiacea 1*11 Species r »nges Fig. 8 Schematic diagram of the distribution Fig. 7 Percentages of taxa (totals, Euphausiacea: ranges of planktonic organisms es referred to 38, Chaetognatha 18) present In part of the water masses (see aiso Table I ). water mas3 (white, A), in the entire water mass (black, B), and restricted to the water mass (not occurring in other water masses, but not present Globorotalia truncatulinoides and Ô. in ali parts of this one ( hatched, C). 1 : Subarctic; inflata( E. Boltovskoy, 1981b). 2 : Western North Central; 3 : Eastern North But Subantarctic and Subtropical expatriates Central; 4 : Transition; 5 : Equatorial; 6 : make up anywhere from 70-80 to >90£ of the Western South; 7 : Eastern South. (Bssed on overall Inventory. Given the fact that they ore distribution chsrts by Brinton, 1962; Blerl, expatriates from other systems it is safe to 1959). assume that they are not adapted to the Transltlon. Samples collected in this area usually have very other communities. In most major oceanic high proportions of juveniles (Pteropoda), systems semi-closed recirculating patterns allow sexually Immature (Chaetognatha), and deformed the organisms to maintain their ranges, reproduce (Foraminifera) specimens; this strongly suggests and, probably, evolve jointly (see, however, that the expatriates do not reproduce here Mar galef, 1967;Hædrich & Judkins, 1979; Yan (Margalef, 1967). Therefore, there most der Spoel & Hey man, 1983). In contrast, probably is not genetic specialization and one can Transition zones seem to be quite different in this assume that their interrelationships are neither respect. es frequent nor os specialized as the ones they In the Transition zone of the SWA most maintain with members of their original Subtropical and Subantarctic species consistently communities, within the latter. Even the ties occur in the or eo. Some show incipient adaptations between organisms of Identical procedence can be to these local conditions (see Yan der Spoel & expected to be looser here than in their original Boltovskoy. 1981); but have their distribution media: environmental differences end mixture centers elsewhere; and a few species with broader with an heterotopic assemblage can modify the total ranges have maximum densities in the physiological and ethological responses consider Transition, for example, the foraminifera ably (e.g., lack of mating). Fig. 6 Distribution ranges of 26 euphausild taxa (thin lines) and water mass boundaries (hatched areas) in the Pacific. The species limits coincident with water mass boundaries are not shown. (Redrawn from Brinton, 1962). -22- On the other hand tho relationship among endemics and of the latter toward the Immigrants are probably more firmly established. Figure 9, based on these speculations, suggests that, for overall relationships in the Transition to be comparably close and specialized as in typical communities, endemics and “ semi-endemics" should be numerically totally dominant over pooled expatriates; in the SWA this certainly is not the case. These considerations incline me to conclude that the Transition assemblage is not comparable with full scale communities, although it has a precisely definable biotope, and aiso some peculiar species. Some of the changes that take place in this type of areas resemble replacements of entire commun ities, rather than variations within a single community (e.g, Yenrick, 1971). Beklemishev ( 1969) pointed out that Transition areas are in a state of dynamic equilibrium being continuously generated at one end and destroyed at the other. CONCLUDINO REMARKS Throughout this review I tried to point out end/or furnish evidence of the following: 1. That biological tracers and sensors are adequate tools for some hydrological aplications, but their Fig 9 Hypothetic scheme of the relationships use can be misleading when working on the between organisms in planktonic communities (A, biogeography of ecological units. Biologists tend to B) and in a Transition zone (T). Specialized use indicator species for hydrologic (current and Interactions (thick arrows) are dominant In the water mass) studies and for biogeographic former; when members of the communities purposes interchangeable, to the point that In become expatriates in a Transition , their mutual semes cases it is not clear whether a particular ties, and especially those with the expatriates of zonation proposed refers to water types or to different origin and with local inhabitants become biogeographic areas. These two concepts are not looser and circumstantial (thin arrows). synonymous. Assuming that the Transition hosts equal 2. That the distribution of most planktonic species proportions of endemics and expatriates of and pelagic communities is associated with, but different communities, 2/3 of the Interactions hardly ever restricted to or spread throughout an are here non-specializad. entire water mass. The match "species distribution - water mass" is poor for the greet majority of the plankters. functional differences with non-transitional 3. That TS-defined water masses and currents are assemblages. related with the position and boundaries of pelagic For the SWA, with the exception of "Meteor’s “ communities, but water mass patterns are not work, extensive and thorough distributional coincident with the patterns of the communities. investigations were carried out only with 4. That transitional assemblages have important Foraminifera. However, these were aimed at the -23- stud/ of circulation patterns, rather than at okeene. Nauka, Moskva : 320 pp. ecologically oriented biogeographic analyses. Most -BOLTOVSKOY, D., 1978. Caracteristicas biogeo- other schemes seem to have been defined on the gréflcas del Atléntlco Sudoeste: plancton. Physis basis of " unnatural boundaries" inasmuch the (Buenos Aires). A 33 : 67-90. latter exist though an a priori definition (l.e., -BOLTOVSKOY. D., 1979. Zooplankton or the south current and water mass patterns). In con western Atlantic. South African J. Sei., 75 : 541-544. sequence, with a few exceptions the coincidences -BOLTOVSKOY. D., 1981. Caracteristicas biológicas between the latter seem to arise from the del Atléntlco Sudocddental. In: D. Boltovskoy (ed.), acknowledgement of the divisions derived from Atlas del zooplencton de! A tl én tico physical studies, rather than from proven Sudoccidentel. Puhi. Esp. INIDEP. Argentina : dissimilarities between the distributions and/or 239-251. abundances of the groups concerned. In fact, for -BOLTOVSKOY. E„ 1959. La corrlente de Malvinas most taxa the information is simply not yet (un estudio en base a la investigation de available for any more or less meaningful and foramln(feros). Serv. Hidrogr. Neve! thorough analyses. (Argentine), H. IO 15: 96 pp. -BOLTOVSKOY. E„ 1967. Indicadores biológicos en la oceanografie. Cienc. inv. (Buenos Aires), 23 : ACKNOWLEDGEMENTS 66-75. -BOLTOVSKOY, E. 1970. Masas do agua (caracleristlca, dlstribución, movimientos) en la E. Boltovskoy, L. Haury, E. Brinton and C. Lange superficie del Atléntlco Sudoeste, segón indicadores critically reed different versions of the blológicos-foramaniferos. Serv. Hidrogr. Nevel manuscript making valuable suggestions for its (Argentine), H. 643: 99 pp. improvement. -BOLTOVSKOY, E. 1981a. Masas de agu» en el Atléntlco Sudocddental. In: D. Boltovskoy (ed.), Atlas del zooplencton de! At/én tico Sud REFERENCES occidentel. Publ. Esp. INIDEP. Argentina: 227-237. -BOLTOVSKOY, E. 1981b. Foraminifera. In: D. -ALVARINO, A.. 1981. Siphonophorae. In : D. Boltovskoy (ed.). Allas del zooplencton del Boltovskoy (od.) Allas del zooplencton del Atlantica Sudoccidentel. Puhi. Esp. INIDEP, AtIdnlfco Sudoccidentel. Puhi. Esp. INIDEP, Argentina: 317-352. Argentina: 383-441. -BRINTON. E., 1962. The distribution of Pacific -AN6EL, M. V., 1981. Ostracoda. In: 0. Boltovskoy euphausiids. Buil. Scripps last. Oceana gr., 6 : (ed.) Alles del zooplencton del At Idai leo 51-270. Sudoccidentel. Puhi. Esp. INIDEP. Argentina: -CONOVER, R. J., 1979. Secondary production as an 543-585. ecological phenomenon. In : S. Van der Spoel ik A. C. -ANTEZANA, T. S. E. BRINTON. 1981. Euphausiacea. Pierrot-Bults (eds), Zoogeography end divers In: D. Boltovskoy (ed.), Allés del zooplencton del ity of plankton. Bunge Sei. Puhi., Utrecht : 50-86. At/dntico Sudoccidentel. Puhi. Esp. INIDEP. -DADON. J. R. 8> D. BOLTOVSKOY. 1982. Zoo- Argentina : 681-698 . planktonic recurrent groups (Pteropoda, Eu -BEKLEMISHEV. C. W.. 1969. Ekologiye i bio- phausiacea, Chaetognatha) in the Southwestern geogrefiye pelagia!!. Nodti, Moskva : 291 pp. Atlantic Ocean. Physis (Buenos Aires), A, 4t : -BIERI. R.. 1959. Tha distribution of the planktonic 63-83. Chaetognatha and their relationship Io water masses. -FAGER, E. W., 1963. Communities of organisms. In: Limnol. Oceonogr., 4\ 1-28. M. N. Hill (ed.) The See. 2. Interscience Publ., N.Y. : -BJÔRNBERG, T. S. K.. 1981. Copepoda. In : 415-437. D Boltovskoy (ed.), A ties del zooplencton del -FAGER, E. W. & J. A. MCGOWAN. 1963. Zooplankton Atlantica Sudoccidentel. Publ. Esp. INIDEP. species groups In the North Pacific. Science, t40 : Argentina: 587-679. 453-460. -BOGDANOV, D. V.. 1961. Map of the natural zones of -GORSHKOV, A.A. (ed.). 1977. Atlas Okeenov. the ocean. Okeenologfye. 1: 941-943. At/enticheskii i Indiiskii Okeeny. Min. Oborony -6060R0V, V. G., 1974. Plankton mirovogo SSSR, Voenno-Morskoi Flot : 306 charts + 27 pp. -24- -HAEDRICH, R. L. 6 D. C. JUDKINS, 1979. marine life. In : H. Cher nock & G. E. R. Deacon (eds), Macrozooplankton and its environment. In : S. Van der Advances in oceanography. Plenum Press. N.Y. : Spoel & A. C. Pierrot-Bults (eds), Zoogeography 65-130. end diversity of plankton. Bunge Sei. Publ. -VAN SOEST, R. W. M.. 1979. North-south diversity. Utrecht: 4-28. In: S. Van der Spoel & A. C. Pierrot-Bults (eds). -HE NT SCHEL, E„ 1938. Das Netzplankton des Zoogeography and diversity or plankton. Südatlantischen Ozeans. Eina Zusarrmenfassung. Bunge Sei. Puhi. Utrecht : 103-111 . Wiss. Ergbn. dt. At/. Exped. "Meteor', -SOUTO, S., 1981. Tintinnina . In: D. Boltovskoy 1925-/927, 13: 245-308. (ed.), Allas del zooplencton del Atlantica -HENTSCHEL, E. 1942. Eina biologische Karle des Sudoccidentel. Puhi. Esp. INIDEP, Argentina : Allaniischen Ozeans. Zool. Am., t37: 103-123. 353-381. -JOHNSON, M. W. & E. BRINTON, 1963. Biological -STEUER, A., 1933. Zur planmasslgen Erforschung species, water masses and currents. In: M. N. HUI der geogr ophis Chen Verbreitung des Hallplanktons, (ed.) The See. 2. Inlerscience Publ., N.Y. : besonders der Copepoden. Zoogeogrephice, / : 381-414. 269-302. -KOBLENTZ-MISHKE, O.J., V. V. VOLKOVINSKY8» J. 6. -SVERDRUP. H. U.. M. W. JOHNSON 8, R. H. FLEMING. KABANOVA. 1970. Plwiklon primary production of the 1942. The oceans, their physics, chemistry World Ocean. In: W. S. Wooster (ed.). Scientific and general biology. Prentice Hall, N.Y. : exploration of the South Pacific. Nat. Acad. 1087pp. Sei., Washington : 183-193. -VAN DER SPOEL, S. & D. BOLTOVSKOY, 1981. -KRAMP, P. L, 1957. Hydromedusae of the Discovery Pteropoda. In: D. Boltovskoy (ed.), Atlas del collection. Disc. Rep., 29: 1-128. zooplencton del A Han tico Sudoccidentel. -MARGALEF, R„ 1967. Some concepts relative to Ura Puhi. Esp. INIDEP. Argentina : 493-524. organization of plankton. Oceenogr. Mar. Bio/. -VAN DER SPOEL, S. 8. R. P. HEYMAN. 1983. A Ann. Rev., 5 : 257-289. comparitive alias of zooplankton. Springer -MCGOWAN, J. A. 1971. Oceanic biogeography of Ura Verlag, Berlin: 186 pp. Pacific. In : B. M. Funnell & W. R. Riedel (eds). The -VENRICK, E. L., 1971. Recurrent groups of diatom Micropaleotology of oceans. Cambridge Univ. species in Ura North Pacific. Ecology, 52 : Press, London : 1-74. 614-625. -MC60WAN, J. A. 1974. The nature of oceanic -VINOGRADOV, M. E., 1968. Vertikalnoe raspra- ecosystems. In: C. B. Miller (ed.). The biology of detente okeanicheskogo zooplanktons. Nauka, the oceanic Pacific. Oregon State Univ., Moskva : 320 pp. Corvallis : 9-28. -MCINTYRE. A. 8, A. W. H. BÉ, 1967. Modern Cocco- lithophorldae of Ura Atlantic Ocean. I. Placomia and Cyrloliths. Deep-Sea Rea., 14 : 561-597. -MEISENHEIMER, J.. 1905. Die tlergeographlschen Regionen des Pelagia^, auf 6rund der Verbreitung der Pteropoda. Zoo!. Am., 29: 153-163. -NESIS. N. K., 1974. Okeanicheskie golovonogie mollyuskl yugo-zapadnoi Atlantis. Trudy Inst. Okeanot., 98 : 51-75. -PIERROT-BULTS. A. C. & S. VAN DER SPOEL, 1979. Spéciation in macrozooplankton. In: S. Van der Spoel 6, A. C. Pierrot-Bults (eds), Zoogeography ano diversity of plankton. Bunge Sei. Puhi. Utrecht : 144-167 . -RAMIREZ, F. C. 8. M. 0. ZAMPONI, 1981. Hydro medusae. In: D. Boltovskoy (ed.). Allas del zooplencton del At lani ico Sudoccidentel. Puhi. Esp. INIDEP. Argentina : 443-469. -REID, J. L„ E. BRINTON, A. FLEMINGER, E. L. VENRICK & J. A. MCGOWAN, 1978. Ocean circulation and -25- ON THE EFFECTS OF INTERANNUAL VARIATIONS IN CIRCULATION AND TEMPERATURE UPON THE EUPHAUSIIDS OF THE CALIFORNIA CURRENT. EDWARD BRINTON & JOSEPH L REID Scripps Institution of Oceanography, U.S.A. INTRODUCTION monthly means minus the long-term monthly mean ( Fig. I ). These temperatures are generally Physical characteristics of ocean water-notably well correlated with temperatures in at least that temperature and currents- differ from place to place within a zooplankton species' distributional range (Reid et al., 1978). However, significant departures from temporal regularity in these ♦1.0- characteristics within the total system upon which the species depends for reproduction and growth, would, in the course of time, be expected to initiate departures from existing range and from the adaptations normally employed in + 0.2 -, maintaining range. We have studied the euphausiid crustaceans and their physical environment in the California Current since 1950 and propose, here, to provide examples of changes which have taken -0.2 -> place. A recent environmental variation, El Nino of 1983 to 1985, has been es extreme es any ■r +0.2 - observed so far. The California Current is recognized as being particularly complex biogeographlcally, encom passing its own warm-temperate and subtropical biotas together with intrusions from the eastward flowing North Pacific Drift, the anticyclonic Pacific Central Oyre, and, to a lesser extent, the zonally maintained equatorial water mass. For this reason, and aiso because of its variable, meandering nature and, typically, a seasonal reversal of nearshore flow, this current Is known -0.5 -J es a "system" - the California Current system I I I I I I I I I in ( Reid et al., 1958). System implies order, how ever complex. TIME (yrs) THE TIME SERIES Fig. 1 Six-months running mean time series of temperature, salinity, density and sea-level For most of this century there are records of anomaly at the Scripps pier. Prior to 1925, the temperature, salinity, density, and see level from sea level data are from the San Diego tide gauge. the Scripps pier near San Diego, 33*N. These are Sea level wbs corrected for secular rise and expressed here es anomalies which are the inverse barometer. From Simpson ( 1985). -26- part of the California Current which extends along BIOMASS OF EUPHAUSIIDS IN SYSTEM the southern California coast. The temperature record shows that between During the 1983-1984 period of high water 1915 and 1945 there were more warm episodes temperatures in the California Current, it and of longer duration than cool ones. The recent appeared that ouphausiids constituted a higher period, 1945 to present, has been generally than usual proportion of the total catches. cooler than the mean, but with three prominent Therefore, a comparison wbs made between periods of higher than average temperatures, I ) certain cool and warm periods, using existing late 1957 through 1959, 2) 1976 into early euphausiid biomass data (Isaacs et al, 1969; 1978 (Brinton, 1981) and 3) 1981 to 1984, 1971). January 1955 to April 1957 encom possibly into 1985. passed the cool period of mid-1955 through 1956 (Figs. 1,2a), and mid-1957 through 1959 covered the period which, until 1982-84, wss THE SPECIES known to us as the "warm years" (Figs. 1,2b). In winter (January), summer (July), and Four eupheusiid species are considered of autumn (October), there was little difference particular importance in the California Current: between cool and warm years in euphausiid 1. Fuphausia pacifica extends southward from biomass (ali species combined) (Table I). the subarctic zone, almost to the tropics along January in both cool and warm periods had the Baja California during cool periods (Brinton, lowest concentration. In April, associated with 1962). spring growth to reproductive condition, there 2. The more southern species Nyctiphanes was an Increase in euphausiid biomass in both simplex tends to exhibit e range complementary cool and warm periods; for the cool period, to that of F.pacifica in the California-Baja individual April values were up by factors of 5 to California coastal environments. 15 over January, and individual values for the 3. Euphausia eximia, in this system , is warm period by 3 to 4. Aiso, the proportion of adapted to "cool productive waters marginal to the euphausiid biomsss to the total zooplankton indeed equatorial water mass" (Brinton, 1979). These was greeter In warm periods than In cool periods, three species migrate vertically between the by averages of 14,21 and 21 * for January, July surface layer and 200 or 300m depth (Brinton, and October, respectively, and by 6 55 In April. 1967). Are the Individual species ali responding In 4. Nematoscelis difficilis occupies the concert with increases and decreases in biomass, narrow zone of the oceanic North Pacific Drift 40 or are there year-to-year differences in to 45*N, but, aiso, nearly the full extent of the proportions of species having different biogeo- California Current, 23* to 43*N; hence It Is of graphical affinities- as one would expect? To this limited Interest biogeogrephically within this end, some events of the recent 1983 to 1984 current. warm period will be compared to cool 1952 and The particularly extensive range In the 1956 (F1g.2a). The 1983 Scripps pier temper California Current occupied by N difficilis and atures were above the mean, except in June, while aiso by another cool-water species, Thysa in 1984 they were above the meen except in noessa gregaria may be due to their inhabiting December (Fig. 2c). Along a line of stations depths in and beneath the thermocllne (Brinton, extending westward through the southern 1967). On the other hand, E.pacifica enters the California bight past Point Conception (Fig.3a), mixed layer at night and, therefore, aiso may be cool-water Euphausia pacifica appeared limiter) towerd the south by mixed layer strongly dominant in April 1956, and was tempr^ures - as may be the warm-water important, even in January (Fig.3b). At the same vertical migrators at their northern limits. time, the more southern coastal species Nyctiphanes simplex was scarce and the southern, more oceanic species Euphausia -27- mid-Baja California, 25-30*N. 1952 & 1956 In contrast, during 1984 (January, April) Nyctiphanes simplex was the dominant euphausiid, particularly inshore (Fig. 3c), while £.eximia penetrated the area from the south, as during 1983. BIOMASS AND DISTRIBUTION When examining a shift in the limits of distribution of a species, it Is useful to consider whether there has been a change in the population density (e.g., as with the Pacific sardine, CalCOFI Rep., 1960: 8-1). High abundance might lead to spreading beyond limits exhibited during times of low abundance. January distributions from 1969, an undistinguished year with respect to temperature, will be compared with the warm Januaries of 1978 and 1984 (Fig. 4). E.pacifica, in January 1969, extended south ward to 30*N, near Guadalupe Island, evidently occupying the main stream of the California Current. In the brief warm period of early 1978 the southern, offshore limit of range had retracted from the 1969 limit only by about 200km, while I" T I II overall biomass remained nearly the same es In 1969, 1.9g/m2. In the longer 1983-84 warm period, the January range limit differed little from that of similarly warm 1978, but 1984 mean biomass was much less, 0.2g/m2, after more than a full year of above-average temperature. In contrast, biomess of N. simp lex was about five times higher during the two warm Januaries (1978, 1984)'than during January 1969. It should be noted that, during midwinter, northerly flow along the coa3t Is a typical feature of the California Current ( Reid et al., 1958). Such flow T—1—I—I—T—I—r extends the northern limit of N. simplex beyond J F M A M J J 0 N D our sampling grid ( F1g.4), while variation in the offshore limit is better documented. Fig. 2 Scripps pier temperature. Long-term Evidence that the interannual differences In monthly mean (1917-1980) and means for A. biomass are largely a consequence of changes in 1952 and 1956; B. 1957, 1958 and 1959; C. abundance rather than in age structure of the 1983, 1984. population is to be seen in figure 5. For ali body lengths of both species Itera was, roughly, a exim fonto absent - evidently not reaching this tenfold difference in abundance between 1969 and far north from its usual density center off 1984, although in 1984 N. simplex seems to -28- Table I Euphausiid biomass ( wetweighl)*, as a proportion of total zooplankton biomass. California Current cool period (Jan.1955-April 1957) compared with warm period (July 1957 through 1959) WEI6HT OF EUPHAUSIIDS WEI6HT OF EUPHAUSIIDS AS X OF PERIOD gm/m^ WEIGHT OF TOTAL ZOOPLANKTON X X RANGE XXX INCREASE. WARM PERIODS JANUARY COOL 2.1. 3.2. 1.1 2.1 17-27 20 i4 WARM 1.1. 1.8 f.5 24-44 34 APRIL COOL 9.9.21.0.16.7 IS.9 42-51 48 6 WARM 4.6. S.S S.O 50-57 54 JULY COOL 3.2. 2.9 3.1 7-12 9 21 WARM 1.9. 3.1. 4.2 3.1 13-46 30 OCTOBER COOL 3.1. 4.6 3.8 13-18 15 2Î WARM 2.5. 1.3. 3.1 2.3 29-40 36 "Valueshave been adjusted for: 1) observed night/day proportions (CalCofi Atlases Nos. IO. 14. 21), and 2) 1m ring net/ Bongo net catch ratio for Euphausiid biomass, X= 1/2 (Brinton fit Townsend, 1981). have age groups at 6 and 10-11 mm bod/ length species, N. simplex and £. eximia, having which were indistinct in 1969. shifted northward as the waters wormed, then Euphausia eximia is not often an important spread broadly toward the west at the break in the member of the zooplankton off California, usually coastline at Point Conception. being south off 30*N in Mexican waters. However, The 1983 warming off southern California we considered (Fig.3) that its presence off continued into 1984 (Fig.2c). This was associated southern California during 1983-1984 was with a large, sluggish, oblong eddy situated in and significant evidence that there was northward off the bight (Fig.7b). In April 1984, strong, transport of oceanic ss well as of neritic water. southward flow resumed along central California E.eximia tended to be concentrated seaward of (35-38*N), but not off southern California coastal N. simplex off Baja California, and (F1g.7c). Anomalies of steric height for cruises extended northward, though not nearly as far as during the warm periods 1983 and 1958 better N.simplex, during the warm periods of early illustrate deviations from means. In early 1983 1978 and 1984 (Fig. 6). There were cor (F1g.8a) measurements of steric height were responding increases in biomass (over January above the seasonal mean from central Californian 1969) in the zone north of station line 110 waters to northern Baja California. Highest (29*N). anomalies were generally nearest to shore, Examples of flow in the Californio Current reaching 14 dynamic centimeters to the north of during El Nino of 1983 to 1984 show that in Point Concplion and off southern California. Such early 1983 (Fig.7a), northerly flow from the northward coastal flow resembled that of 1958 southern California bight was directed westward, (Fig. 8b). then northward beyond Point Conception. Such In the above discussion, the relatively flow is clearly associated with the westward bulge numerous euphausiid species ( e.g. Thysanopoda of the distributions of species in that region (Figs. astylata, Euphausia hemigibba, Nemato 4, 6) observed during early 1984. The southern scelis tenella, Stylocheiron carinatum) -29- Fig. 3 Station by station proportions along, A. station line 90 off southern California of the northern, cool water euphausiid Euphausia pacifica and the southern, warm water species Nyctiphanes simplex and Euphausia eximia. B. cool January 1956 compared with C. warm 1984. of the central water mass have been ignored. This Mention must be made of distributions in a is because they rarely contribute significantly to month other than January. In April, upwelllng Is the California Current community. During the often strongest, particularly off central warm periods, temperatures in the offshore oart California. Southward flow is then strengthened , of the current did not show Increases relative to compared with January. During warm Aprils of seasonal means. The eastward limit of their ranges 1958 and 1984 E,pacifica extended southward lies along lines of fastest flow, well to the west of Into southern California waters, but little beyond the coastal region in which warming was pro (F1g.9). In the cool April of 1962 the range nounced. Thus, species’ range limits tend to lie extended to 27*N off mid-Baja California, and along, not across, isolines of temperatures or biomoss was twice that of the two warmer Aprils. steric height. Conversely, N. simplex W8s well established -30- COOL WATER SPECIES Euphausia pacifica JANUARY ORDINARY YEAR 1969, ANO WARM YEARS (1978,1984) JANUARY ORDINARY YEAR 1969, AND WARM YEARS (1978,1984) Fig 4 California Current distributions during January of northern ( Euphausia pacifici and southern ( Nyctiphanes simplex) euphausllds. The ordinary year 1969 compared with the warm years 1978 and 1984. Average biomass values ara indicated for the area of station line 110 northward. off central and southern California In April of Montery Bay(36*N). warm 1958 and 1985, but not in cool 1962 An animal which is more passive and short (F1g9). Overall biomoss W8s low in 1962, lived than theeuphausiids, the typically offshore, 0.01g/m2 north of line 11O and 0.13g/m2 when warm-subtropical, pelagic tunicate Doliolum the full range to the south was included. This denticulatum examined by Berner & Reid latter Is still far lower than 3.98g/m2 recorded (1961), showed little' seasonal change in for April 1984, which included new population distribution during cool years, prior to 1957, centers in the southern California bight and thereby resembling the euphausllds. Seasonal temperature Fig. distributional extended too with California eximia, and part Fig. 1959, 1000 m CALIFORNIA 6 M short warm 5 '75* of California simplex, this Length the ordinary warm LENGTH-FREQUENCY Current, COMPARED 1984. doliolid a changes California CURRENT, response. Eud^jjs term frequency Current period ordinary (cf. i?0* BODY year eo. penetrated j were WITH pc:^'Co 27-38°N Fig. to LENGTH 29-38 Current 1969 distributions of WARM interpreted 4). However, bring distributions DISTRIBUTIONS year (mm) mid- compared 4 ORDINARY ni* N,for YEAR a 1969 previously north 1957 Nycf'C^O-tes GRD'NARY THE about 1984 during E.pacifica and as SOUTHERN i26 FOR YEAR compared with 4 of being through for YEAR average S j rrf Point much 1969 warm 'ê cool OFFSHORE (1969) the the i of -31- ANO biomass i?o* 1978 SPECIES WARM vertically across generally column during copepods Oopalakrishnan, where euphausiids temperature responses (Brinton, under central euphausiid individual This hera, this Conception 400km. to 1984), YEARS We and Thus, Euphov include values extent appears have 0978,1984) 1984. have monsoon $>0 currents having unfavorable euphausiids. their many Seasonal M5* while species Cumia for a euphausiid 1975) much seen to may and of been becomes N. which the recent shift to greater ranges. a euphausiid thereby simp that showing then regimes temperature of '25* which have shifts southern undergo and 1973). no the is annual conditions occupy lex, variation unfavorable. be the of species mora span California happened Their undergo broadened have the used Arabian In conservative species euphausiid seasonal but Like shifts same the even than than range i?o* been can capacity when not (Alldredge in diapause South to certain coast. in order exploit Sea its locally is somewhat ocean those about to of the range reversal, upper-level distribution encountered Euphausia 5 (Brintoni the China to biological shown In to at southern climate, systems undergo a 200 iii* Pacific calanid limits, et 1 orient 1984, water depth 0*C less. al., See by œ to , -32- 125° 120° 115° 125° 120° 115° 125° 120° 115#W sieric heimi 4-27 JANUARY 1984 9 APRIL-4 MAY 1984 ( DYN CM ) FEB-MAR 1963 Fig. 7 Steric height 0/500 db in dynamic centimeters for, A. R/V Townsend Cromwell survey 8302-3 (Fig. 1 from Lynn, 1983). B. from 4-27 January 1984, C. for 9 April to 4 May 1984 (from Scripps Inst. Oceanogr. 1984a,b) STERIC HEIGHT MINUS SEASONAL MEAN (DYN. CM.) FEBRUARY- JANUARY 1958 MARCH 1983 Fig. 8 The difference between steric height values and the seasonal mean values in dynamic centimeters. A. Feb.-March 1983 (Fig. 2 from Lynn, 1983). B. January, 1958. -33- APRIL Euphausia pacifica 1958 1962 WARM COOL :OOL NORTH OF PT CONCEP' tST.ViTfO ABuN^CE'tC-OOm’WATER \WARM SOUTH " ■ 0.91 g/m: 1.93 g/m1 0.90g/nV APRIL Nyctiphanes simplex NORTH OF PT CONCEPT 18Tn VARM SOUTH" * 0.05 g/m ,N of line IK) 0.01 g/m2, N 3.98 g/m' 0.14 ' .ali stations 0.13 " .ali Fia. 9 California Current distributions during April 1958, 1962 and 1984 and average biomsss values (Line 1 IO northward) for the southern euphausiid Nyctiphanes simplex and northern Euphausia pacifica. five to ten fold interannual changes in biomass, REFERENCES with southern species dominating in warm times and northern species in cool times. -ALLDREDGE. A. L.. B. H. ROBISON, A. FLEMINGER, J. J. TORRES, J. M. KING & W. M. HAMNER, 1984. Direct sampling and in situ observations of a persistent copepod aggregation in the mesopelagic -34- zone of the Santa Barbara Basin. Mar. Biol., 80 : Advances in Oceanography. Plenum Press, New 75-61. York: 65-130. -BERNER, L. D. & J. L. REID Jr.. 1961. On the -REID. J. L. G. I. RODEN 8» J. G. WYLLIE. 1958. response to changing temperature of the Studies of the California Current SysLem,. CalCOFI temperature-limited plankier Doliolum denticulatum Progress Rep., I July 1956 to Jan. 1958 : 28-57. Quoy and Gaimard 1835. Li mitoi Oceanogr., 6 -SCRIPPS INSTITUTION OF OCEANOGRAPHY. 1984a (2): 205-215. Physical, chemical and biological data. CalCOFI Cruise -6RINTON, E., 1962. The distribution of Pacific 0401. Scripps Inst. Oceanogr. Ref, 84-16 : euphausiids. Bull Scripps Inst. Oceanogr., 8 : 120 pp. 51-270. -SCRIPPS INSTITUTION OF OCEANOGRAPHY. 1904b. -BRINTON, E., 1967. Vertical migration and avoidance Physical, chemical and biological data. CalCOFI capability of euphausiids in the California Current. Cruises 8404, 8405, 8406. Scripps Inst. Limnol. Oceanogr., 12: 451-483. Oceanogr. Ref., 84-25: 1-106. -BRINTON, E., 1975. Euphausiids of southeast Asian -SIMPSON, J. J., 1985. Warm and cold oplsodes in the waters. Naga Rep. Scripps Inst. Oceanogr.,4 California Current: A casa for large-scale (5): 1-287. mid-latitude atmospheric forcing. In: Proc. Ninth -BRINTON, E., 1979. Parameters relating to the Annual Climate Diagnostics Workshop, distributions of planktonic organisms, especially Corvallis, Oregon, 22-26 October 1984. U.S.Dept. of euphausiids in the eastern tropical Pacific. Prog. Commerce, NOAA, Wash. : 173-184. Oceanogr., THE GENETIC STRUCTURE OF ZOOPLANKTON POPULATIONS ANN BUCKLIN College of Narine Studies, University of Delaware, Lewes, U.SA INTRODUCTION and quantitative solutions require estimates of migration rates among populations. Extensive biogeogrophic ranges ere character Given the subtle and changeable nature of istics of zooplankton species (Van der Spoel & potential barriers to gene flow in planktonic Heyman, 1983). Some oceanic species' environments, it seems fruitless to attempt to distributions include both the Atlantic and Pacific exactly delimit the spatial extent and size of a Oceons and/or both hemispheres. However, an local population of a zooplankton species. Rather, individual's dispersal capabilities may be limited descriptions of structure must rely on statistical relative to the species' range. Random inter analyses of geographic patterns of genetic breeding across the species is consequently either variability across a species' range. improbable or impossible, and it becomes useful I will briefly review here previous to determine the extent and size of the "local descriptions of genetic variability In zooplankton populations" (l.e. groups of randomly Inter populations. Although breeding studies are breeding, conspecific individuals) that comprise mentioned, I have focussed this review on studies the species. Restricted gene flow (reproductive of biogeographic patterns of allozymic variability. isolation) among local populations may allow Allozymes are forms of enzymes differing in divergence in their genetic character, so that the electrophoretic mobility. Allozymic variability is species consists of a patchwork of genetically presumed to reflect genetic differences (allelic differentiated local populations. The division of variants of the encoding locus), but variability of the species into reproductively isolated, enzymes with exogenous substrates may result genetically differentiated sub-units is termed from induction or other non-genetic processes genetic structure. (Gillespie & Kojima, 1968; Johnson, 1974). Potential barriers to dispersal in terrestrial Geographic patterns of morphological variation environments may be obvious, including mountain may provide similar evidence of a genetically ranges, rivers, or habitat patchiness, and structured population, but morphological traits genetically structured species populations mey be are presumably more strongly influenced by readily explainable. However, barriers to the environmental conditions. Since allozymes are dispersal of zooplankton in the open ocean are less discrete, quantitative traits, they lend themselves evident. The most probable barriers for well to statistical treatments. planktonic organisms are strong and persistent hydrographic features (e.g. fronts, pycnoclines, rings, gyres). However, the ability of Individuals STATISTICAL ANALYSES OF GENETIC STRUCTURE to cross water msss boundaries is unclear. Additionally, the distance an individual may travel De?cribing the genetic structure of zooplankton and still be integrated into e new population (the populations and inferring patterns of gene flow maximum dispersal range) is difficult if not from spatio-temporal patterns of genetic varia Impossible to estimate for open ocean plankton. bility Isa somewhat Intricate statistical problem. The degree to which populations may be Tests of allozyme frequency heterogeneity, reproductively Isolated by simple distance is thus heterozygote deficiencies and measures of genetic difficult to calculate. This question is theo distance ara conventionally used as indicators of retically interesting, but predictive hypotheses the degree of genetic differentiation among natural -30- populations. Following these descriptions, it is Kimurai Weiss ( 1964). According to this model, useful to consider the relationship between correlation of allele frequencies among local genetic differentiation and geographic separation. populations in one-, two- or three-dimensional The rate and smoothness in decay of genetic arrays (with isotropic migration between similarity of local populations separated by adjacent local populations) will decrease with Increasing distances mery reveal the position of distance between local populations at a rate barriers to gene flow and, by comparing rates of dependent upon migration rete. The evidence decay for many taxa, suggest relative dispersal presented above suggests that zooplankton exhibit capabilities. two-dimensional arrays of partially isolated Traditionally, population genetic structure hss populations. If so, Kimura & Weiss (1964) been described using F-statistics based on the predict that the correlation of allozyme amount of inbreeding associated with partial frequencies among local populations will decay reproductive isolation of local populations logarithmically. This prediction has not been (Wright, 1951, 1965). Calculations of F- widely tested, but a single study is discussed statistics for multiple leei (Nei, 1977) roly on below. comparisons between heterozygosity observed (the frequency of tieterozygotes averaged across ali loci) in individual and pooled collections and CAUSES OF DIVERGENCE heterozygosity expected with random mating across ali populations sampled (Levenee, 1949). The causes of genetic divergence of local Population structuring decreases heterozygosity, populations are various, and include differential as described by the Wahlund Effect (Wahlund, selection on local populations and genetic drift 1928): Aa » 2 p q - Vg (where Vg is the (the accumulation of random changes in genetic variance of the less_common allele among local characters). The driving forces behind genetic populations, and p and q are mean allele differentiation and the relative contributions of frequences for the poo’ed collections). Thus, selection end drift may be difficult or impossible heterozygote deficiencies across numerous leei to establish. are Indicative of genetic structure (Wright, The magnitude of drift is a statistical function 1969). (derived from the expected variance in allele Other statistical means of describing population frequency) determined primarily by the size of genetic structure are based on comparisons of the offspring generation, according to the allozyme frequencies among ali collections. As a function: V-» p q/2N ( where Vg is the variance in first approximation, frequencies mey be allele frequency after one germtion, p and q are compared by a statistical test of heterogeneity, the the frequencies of the alternate alleles at a give O-test (Sokol & Rohlf, 1981). Moro powerful locus, and N is the size of the offspring statistics have been developed specifically for generation). For populations of 1000 or greeter, genetic data, Including an array of genetic distance drift is negligible regardless of allele frequencies. measures. A frequently used distance measure D Bottlenecks and other events during which drift (Nei, 1972) has been used for a wide variety of may strongly alter allele frequencies would seem taxa, and values have been approximately unlikely for zooplankton populations, making correlated with taxonomic separation (races, them largely Immune to random genetic subspecies, species) (Thorpe, 1983). fluctuations. There Is, however, one situation An additional means of describing genetic when drift may be significant even for large structure Is by comparison with predictions of populations. When individual contribution to theoretical models of gene flow. One of the recruitment is highly variable (es is typical of simplest models of population genetic structure, many invertebrate, Including planktonic end one that is appropriate to the planktonic Crustacea), the effective population size Is very environment, Is the "stepping-stone" model of small ( Wright, 1969) and Vg mey be Kimura (1963), with quantitative analysis by considerable regardless of the number of -37- potential ly reproductive individuals. species are distinctly structured on the largest A second primary force driving genetic diverg scale, and perhaps consist of distinct, ence of populations is selection. Differential geographically isolated species. selection in different portions of a species' range Studies of geographic variability of allozymic may result in regional differences in a species. It frequencies have aiso provided evidence of genetic is unlikely that selection on a single enzyme locus structure in zooplankton populations. Sub might structure a species, and allozymic division of the species into local populations, variability may be considered to track, not drive, which are only partially reproductively isolated differentiation. ( For this reason, allozymes are and may correspond to distinct races, usually frequently treated as selectively neutral and are occurs on smaller geographic scales than the regarded es “markers" of population phenomena). inter-ocean differences demonstrated by breeding The selective neutrality of the traits used to experiments. Intertidal tide pool populations of describe population genetic structure is of the harpactacoid copepod, Tigriopus considerable importance, since estimates of gene californicus, show strong differentiation flow and migration may then be derived directly ( (divergence of allozyme frequencies at several Wright, 1969). Alternatively, the selection enzyme loci) among nearby pools (Burton et al., coefficients of non-neutral traits must be 1979; Burton & Feldman, 1981), Indicating determined, which may be impossible. However, structuring on a very small geographic scale. difficulties in establishing causes of differen Allozymic frequency differences aiso indicated tiation do not interfere with description of racial differentiation of geographically distrinct population genetic structure. populations of the copepods Tisbe holothuriae, T. clodiensis and T. reticulata In Mediter ranean and N. Atlantic coastal waters (Battaglia & EVIDENCE OF GENETIC STRUCTURE IN Bisol, 1975). Breeding studies confirmed some ZOOPLANKTON SPECIES degree of differentiation among T. reticulata populations, since viability was reduced in Studies of allozymic variation in zooplankton crosses between individuals from different populations have demonstrated that plankton taxa Mediterranean localities (Battaglia, 1957). are highly genetically variable, including Differentiation at the level of genetic races may be copepods (Battaglia et al., 1978; Burton et al., an adaptive response to environmental variation 1979; Bucklin & Marcus, 1985) and euphausiids across a species' range. (Valentine tk Ayala, 1976; Ayala & Valentine, Neritic copepod species are aiso genetically 1979; Fevolden & Ayala, 1981 ; Bucklin & Wlebe, structured. The geographic scale of structuring Is in the press). High variability provides numerous not known, but divergence has been demonstrated allozymic variants for potential indicators of 8t the mesoscale (periodic variation on the order genetic divergence. of weeks to montii and tens to hundreds of km: Experimental studies of interbreeding of con- Stommel, 1963). In a study of allozymic specific but distantly separated Individuals have variation at loci encoding four enzymes In the provided evidence of genetic differentiation. calanoid copepod, Labidocera aestiva, the Laboratory crosses between eastern and western species was demonstrated to be highly genetically Atlantic conspeciflc Individuals yielded viable variable (Bucklin A Marcus, 1985). Further, offspring for four species of the harpactacoid samples collected in three regions from Cepa Cod copepod, Tisbe, but crosses between individuals to Florida along the east coast of the U.S.A. of another species, T. clodiensis, produced no exhibited significant genetic differentiation. offspring (Battaglia & Yolkmenn-Rocco, 1973). First, there were almost fixed differences in Similarly, crosses between Atlantic and Pacific allozyme frequencies at one enzyme locus, which Individuals of the calanoid copepod, Acartia were highly significant by a G-test (Sokal & clausi, wera unproductive ( Carillo et al., Rohlf, 1981). Second, values of the statistic of 1974). Clearly, what ara now considered to be genetic distance, 0(Ne1,1972), averaged 0.201 -38- standerd deviation of 0.08, reflecting divergence examine theoretical predictions of gene flow using to at least reproductively isolated local 8llozymic data. populations (Ayala, 1975). And third, there were highly significant heterozygote deficiencies, EUPHAUSIIDS OF THE NORTH ATLANTIC SLOPE WATER compared to heterozygote frequences expected Allozymic analysis of seven samples of the with random mating (Levene, 1949), at five loci. euphausiids, Euphausia krohnii and Differentiation at this scale may be best explained Nematoscelis megalops, collected between by geograpic separation resulting- in isolation by October 1981 and October 1982 in a 300 by 700 distance (Wright, 1943). Gene flow among the km area of the western North Atlantic Slope water three regions must be limited to allow genetic revealed high level of genetic variability ( Bucklin divergence of the populations. Genetic divergence & Wiebe, in the press). Based on data from eight may be driven by differential selection in the loci encoding five enzymes, both species were three regions along the species' extensive highly polymorphic and heterozygous. Allozymic latitudinal range. frequencies differed significantly among the seven collections by the G-test (Sokal & Rohlf, 1981), indicating significant heterogeneity of successive GENETIC STRUCTURE OF EUPHAUSIID samples of each species (0u(132) = 791.5 for E. POPULATIONS krohniiunA 0^(125) ■ 563.8 for N. megalops, P<0.001 for bothi. Genetic distances ( D, Nei, Studies of patterns of allozymic variability in 1972) among samples of each species were euphausiids, a prevalent planktonic taxon in typical of distances tetween local populations coastal and oceanic waters, have aiso revealed (mean D between samples of E.krohnii was D~ evidence of genetic structure. Several species of 0.116 +_ 0.112 and between samples of N.mega/ops D-0.203 +.0.073). intraspecific Euphausia have been assayed for allozymic variability among populations: E. distinguenda, genetic distances were not the result of sampling a tropical species, showed some differentiation error: spurious genetic distance from sampling between samples separated by three degrees error ( D%, Nei, 1973) was Ds- 0.037 for latitude0.056) (Ayalai Valentine, 1979). E. krohnii ml 0.032 for N. megalops. Another species, E. superba, the large Antarctic The sampling pattern unfortunately does not species, exhibits little allozymic variability allow discrimination of spatial and temporal (Ayala et al., 1975; Fevolden & Ayala, 1981). causes of genetic diverge»we of conspeciflc Perhaps as a result of low variability, there were populations. Allozymic frequencies varied no differences in allozymic frequencies among randomly among the seven collections of each several collections (Fevolden & Ayala, 1981), species (Fig. 1 ). and thus no apparent genetic structuring. Random variation may be explained by spatial Structuring of oceanic zooplankton populations paUhlness In both species populations, by suggests that hydrographic features (such as temporal fluctuations in the genetic character of eddies, fronts or current boundaries), geographic the populations, or both. distance or other biological or physical phenomena may prevent random Interbreeding EUPHAUSIA PACIFICA IN THE CALIFORNIA CURRENT across planktonic species. Determination of the The euphausiid, Euphausia pacifica, Is scale of structuring will require appropriately frequently the most abundant euphausiid of the designed sampling programs. California Current, es well 83 the predominant Outlines of the results end conclusions of two zooplankter in terms of biomass (Brinton, descriptions of the genetic structure of euphausiid 1962). . populations follow. These are attempts to Dense aggregations, which may correspond to determine the spatial and temporal scale of genetic local populations, occur in submarine canyons structure in zooplankton populations and to along the California coast. Recruitment is tied to o 0.4 Ld -0.2 < -0.4 W -0.6 - 1-2 2-3 3-4 4-5 6-7 23 3-4 4-5 5-6 6-7 7-8 COLLECTION Fig. 1 Differences in frequencies of the most common allozyme (allele) of each locus between successive collections of the euphausiids, Euphausia krohnii and Nematusceiis megalops, from tho western North Atlantic Slope Water. Seven collections were made in 1981 and 1982, with an additional collection In August, 1984. Allozyme frequency changes at each enzyme locus for successive samples were calculated as P(t+ j) - p(t), where p is the allozyme frequency in each sample, and t is the sample number. Collection dete corresponding to each number are: 1 ) 27 October 1981,2) 24 November 1981, 3) 12 December 1981, 4) 15 December 1981, 5) 8 February 1981,6) 16 August 1981, 7) 5/6 October 1982, 8)10/11 August 1984. Numbers along the abcissa indicate allozyme frequency changes between samples 1 and 2, etc. Missing sample numbers indicate absence of the species from that collection. upwelling intensity and is apparently local, with collections by techniques of Nei ( 1972). lvalues multiple centers of recruitment along the averaged 0.175 ± standard deviation of 0.107. California coast (Brinton, 1976). The persist Thia reflects significant genetic differentiation of ence and geographic stability of aggregations samples collected over a short geographic range. suggests that the species might be genetically Clearly the species is genetically structured, and structured. it now becomes interesting to look for statistical Semples of Euphausia pacifica were relationships between allozymic frequencies and collected along a north-south transect from just geographic separation. Decrease in the correlation north of Point Conception to San Diego in October of allozyme frequencies between samples over 1984. distance was determined es a test of predictions of Collections at six sites were made In association the stepping-stone model of gene flow (Kimura, with the California Cooperative Fisheries 1952; Kimura & Weiss, 1964). The decreese In Investigations (CalCOFI), which samples a grid of correlation was approximately logarithmic with stations quarterly. Eight of nine loci encoding distance (r = - 0.77, P<0.05) (Fig. 2), eight enzymes assayed for allozymic variability suggesting that Eopacifica local populations were polymorphic. Genetic distances were approximate a two-dimensional arrey with calculated for pairwise comparisons among ali isotropic migration between adjacent populations. -40- restricted gene flow among conspecific popul ations, and give rise to genetically structured species populations. REFERENCES -AYALA, F. J., 1975. 6enetlc differentiation during the spéciation process. Evo/. Bio!., B: 1-70. -AYALA. F. J. 8* J. W. VALENTINE. 1979. Genetic .------1------1______1______, variability in the pelagic environment: a paradox? 03 230 303 ‘500 DiSTAf.cr C K».‘) Ecology, 60: 24-29. -6ATTAGLIA, B., 1957. Ecological differentiation and incipient intraspecific isolation in marine copepods. Fig. 2 Regression analysis of allozymic varia Ann. Bio!., 33: 259-260. bility of the euphausiid, Euphausia pacifica, -BATTAGLIA. B. & P. M. BISOL. 1975. Biochemical in six samples collected along a 400km polymorphisms In marine crustaceans In relation Io north-south transect in the California Current. their ecology. In : H. Barnes (ed.). Proc. Ninth The value of the correlation coefficient for each Europ. mar. biol. Symp., 1975. Aberdeen Unlv. comparison of allozyme frequencies in two Press : 573-585. samples is graphed against distance separating the -BATTAGLIA. B.. P. M. BISOL & 6. FAVA. 1970. collection sites. The line is the function best 6enetic variablis in relation Io the environment in fitting the data (r= -0.77, P<0.05). Such a some marine Invertebreates. In: B. Battaglia and JA Beerdmore (eds.), Marino Organisms. Plenum logarithmic relationship conforms to the Press. New York : 53-70. theoretical expectations of Kimura & Weiss BATTA6ÜA. B. & B. VOLKMANN-ROCCO. 1973. ( 1964) for genetic structuring of a species Geographic and reproductive isolation In Um marine distributed œ a two-dimensional array of local harpactacoid copepod Tisbe. Mar. Biot., !9 : populations with isotropic migration between 156-160. adjacent populations. -BRINTON. E.. 1962. The distribution of Pacific euphausiids.. Bull. Scripps inst. Oceanogr.. 6 : 51-270. -BRINTON, E., 1976. Population biology of Euphausia CONCLUSION pacifica off Southern California. Fish. Bull., 74 : 733-762. Although causes of differentiation cannot be -BUCKLIN, A. & N. H. MARCUS, 198S. Genetic determined, the allozymic data indicate that differentiation .of populations of the planktonic copepod zooplankton species may be structured on small Labidocera aestiva. Mar. Bio!., 84: 219-224. spatial and temporal scales. Evidence of genetic -BUCKLIN, A. & P. H. WIEBE. in the press. Genetic structuring of nearly ali of the species studied heterogeneity in euphausiid populations: Euphausia suggests that panmixia across zooplankton species krohnii and Nematocells megalops in the North is not usual. The most Important conclusion from Atlantic Slope Water. Limnot. Oceanogr. these studies is that the genetic homogeneity of -BURTON, R. S., M. W. FELDMAN 6. J. W. CURTSIN6ER, 1979. Population genetics of Tigriopus zooplankton populations over even short distances californicus (Copepoda!: Harpaelacolda). I. Population cannot be assumed. There may be barriers to genetic structure along Uva central California coast. dispersal In plankton environments, including Mar. Eco!. Progr. Ser., / : 29-39. physical or hydrographic features, biological -BURTON. R. S. 8, M. W. FELDMAN, 1981. Population differences among conspecific populations, or genetics of Tigriopus californicus. II. Differentiation geographic distances between populations may be among neighboring populations. Evolution, 35 : too great to be spanned by Individual dispersal. 1192-1205. Any or ali of these factors mery result in -CARILLO B. G. E.. C. B. MILLER 8, P. H. WIEBE, 1974. -41- Failure of interbreeding between Atlantic and Pacific Hérédités, //: 65-106. populations of the marine calanoid copepod Acartia -WRIGHT, S., 1943. Isolation by distance. Genetics, clausi Glesbrecht. Limnof. Oceanogr., 19 : 28: 114-138. 452-458. -WRI6HT, S., 1951. The genetical structure of -FEVOLDEN. S. E. & F. J. AYALA. 1981. Enzyme populations. Ann. Cugen., IS: 323-354. polymorphism in Antarctic krill (Euphausiacea): -WRIGHT, S., 1965. The interpretation of population genetic variation between populations and species. structure by F-stalistics with special regard Io Sarsia, 66 : 167-182. systems of mating. Evolution, 19: 395-420. -GILLESPIE. J. H. 5. K. KOJIMA. 1968. The degree of -WRIGHT, S., 1969. Evolution and the Genetics of polymorphisms in enzymes involved in energy Populations: Vol.2. The Univ. of Chicago Press : production compared to thai in non-specific enzymes 511pp. in two Drosophila ananassae populations. Proc. Pai. Acad. Sei.. 6t: 582-585. -JOHNSON, G. B., 1974. Enzyme polymorphism and metabolism. Science, t84: 28-37. -KIMlfftA, M., 1953. The 'stepping stone' model of a population. Report Pain inst. 6enetics, Misima 3: 62-63. -KIMURA. M. 8» G. H. WEISS. 1964. The stepping stone model of population structure and the decrease of genetic correlation with distance. Genetics, 49 : 561-576. -LEVENE, H.. 1949. On a matching problem arising In genetics. Ann. Matti. Slat., 20: 91-94. -NEI. M„ 1972. Genetic distance between populations. Am. Pat. 106: 283-292. -NEI, M.. 1973. The theory and estimation of genetic distance. In: N. E. Morton (ed.), Genetic Structure of Populations. Unlv. Hawaii : 45-54. -NEI, M„ 1977. F.statistics and analysis of gene diversity in sub-divided populations. Ann. Hum. Gen., 4! : 225-233. -SOKAL. R. R. & F. J. ROHLF, 1981. Biometry. W.H.Freeman, San Francisco : 859pp. -STOMMEL. H.. 1963. Varieties or oceanographic experience. Science. 139 : 572-576. -THORPE. J. P., 1983. Enzyme variation, genetic distance and evolutionary divergence in relation to levels of taxonomic separation. In: 6.S. Oxford & D.Rolllnson (eds), Protein Polymorphism: Adaptive and Taxonomic Significance. Academic Press, New York : 131-152. -VALENTINE. J. W. 8, F. J. AYALA, 1976. 6enetic variability In krill. Proc. Pat. Acad. Sei. 73 : 658-660. -VAN DER SPOEL, S. & R. P. HEYMAN. 1983. A Comparative Atlas of Zooplankton: Biological Patterns in the Ocean. Welensch. Ultg. Bunge, Utrecht : 186pp. -WAHL UNO, S., 1928. Zusammenselzung von Populationen und Korrelationserscheinungen von Standpunkt der Vererbungslehre ausbelrachtet. --42- SIMILARITY OF PLANKTON DISTRIBUTION PATTERNS IN TWO NEARLY LAND-LOCKED SEAS: THE MEDITERRANEAN AND THE RED SEA. Jean-Paul CASANOVA Université de Provence, France. INTRODUCTION 200m, salinities and temperatures stay eround 41 %o and 22*C respectively. Although the plankton populating the Red Sea has Given their physical similarities, it is not not been studied as thoroughly as that of the surprising to find parallel similarities in the Mediterranean, numerous similarities have been patterns of plankton distribution. This report pointed out between them. Indeed there are strong focuses on comparison of four aspects of these analogies between the physical and hydrological biological processes: quantitative, geographical conditions prevailing in these two seas. The and bathymetric distributions snd faunistic relat Mediterranean is connected to the Atlantic by a ions with adjacent oceans. narrow strait about 300m deep. Rapid evaporation in the Eastern basin whose southeastern shore is a desert results in a deficit QUANTITATIVE DISTRIBUTION which is not offset by river drainage and leads to an inflow of water from the Atlantic. In the Jespersen ( 1923) published the first compre Mediterranean, salinity is about 36 °/oo in the hensive study on Mediterranean plankton based on Strait of Gllbraltar and registers a progressive samples collected during the Danish cruises. He easterly increase to about 37 °/oo off Tunisia and showed that planktonic standing crops steadily 38 °/oo at the latitude of Naples. Below 300m, dwindle from west to esst: Bay of Cadiz (Atlantic), salinity end temperature are constant at 39 °/oo Alboran Sea, central sector of the Western Basin, and 13*C respectively. Salinities and tempera Tyrrhenian Sea end Eastern Basin. tures are slightly higher In the Eastern Bæln. The The only exceptions to this pattern ara the outflow of these deep waters forms the Lusitanien enriched zones at the mouths of rivers (Gulf of current in the Northeast Atlantic. Lion, north pert of the Adriatic Sea) end the The smaller Red See is connected to the Indian Ligurian divergence. The main reason for this Ocean by a shallow ( 100m) sill, it consists of a pattern is a shortage of nutrients, especially long narrow basin lying between two arid, phosphates (Sournia, 1973) even in the deep tropical land masses. Evaporation is thus greet water. and salinity is high especially in the northern Thus, ascending currents, divergences and part. Surface currents depend on monsoon winds upwelling do not enhance surface nutrient south of 20*N (Mora», 1970). During the concentrations, except In the Alboran Sea and off winter months, these winds blow south south the North African a»st where the Atlantic inflow easterly end push superficial waters north from h8s relatively high nutrient concentrations. Gaudy the Gulf of Aden. As the water moves northward, (1985), however, recently showed that the its salinity Increases from 36 to 41 %o in the temperate waters of tie Atlantic were not sign north. In the south, deep waters flow out into the ificantly richer in plankton than those of the Indian Ocean. In May, the wind reverses end blows Mediterranean, even In the Eastern Basin. north northwesterly until September. So both the Measurements made In the Red Sea suggest a superficial waters and the deep waters flow out of similar situation. In a recent report, based on a the Red See balanced by an inflow of water at series of hauls extending from the Gulf of Aden to intermediate depths. At depths greater than the centre of the Red Sea, Beckmann ( 1984) noted -43- an overall decrease in plankton from south to authors have reported the occurence of many north exœpt in the shallow waters overlying the immigrant species from the Gulf of Aden (in Hanish SUI where mixing of pelagic and nerftic Halim, 1969), and Beckmann ( 1984) correlated communities resulted in exceptionally high the seasonal presence of copepods such es concentrations. Eucalanus with influxes of oceanic water. In both se8s the biomass of plankton decreases The first data on the distribution of an entire rapidly with depth below 200 to 300m, os planktonic group throughout the Red Sea were for observed by Greze ( 1963) in the Ionian Sea and Chaetognatha (Casanova, 1984). Apart from the Weikert ( 1982) in the centre of the Red Sea. absence of a boreal group, the distributions of the chaetognath species in the Red Sea can be categorised similarly to those of the GEOGRAPHIC DISTRIBUTION OF ORGANISMS Mediterranean (Fig. 1): 1. "Ubiquitous" species, present throughout, from the Strait of Geographical distributions ara better documented Bab-el-Mandeb to the Gulfs of Suez and Aqaba for the Mediterranean. The influx of Atlantic ft.g. Sagitta enflata), 2. "Meridional" species species into the southwest of the Western Basin which live in the superficial layer of the southern was recorded long ago, notably through the quarter of the Red Sea where the oceanic influence presence of the euphausiid Thysanoessa maintains salinity at or below 38 °/oo (e.g. gregaria and the Siphonophora Diphyes Pterosagitta draco), and 3. "Septentrional" dispar(Rn\i6, 1936; Bigelowi Seers, 1937). species, halophilic species which thrive where Accurate data concerning the distribution of salinity is 38 to >41 °/oo in the sectors north of numerous plankton species are available 17- 18*N (e.g. Sagitta pacifica). (pteropoda, Chaetognatha, euphauaiaceena end Thus, both seas have "ubiquitous" species; decapods crustaceans) for the Mediterranean Sea. halophilic species with the "oriental" species of For ali groups, distributions can be classified into the Mediterranean corresponding to the four similar categories; for example, in "septentrional" species of the Red Sea and oceanic Chaetognatha ( Fig. 1 ), Furnesti (1970) species with the "Atlantic" species in the described: 1. "Ubiquitous" species, present in ali Mediterranean and the "meridional" species in the sectors (e.g. Sagitta enflata), 2. "Atlantic" Red Sea indicating the penetration of oceanic species, found along the axis of the inflowing waters. These oceanic species may be represented oceanic waters (e g. Pterosagitta draco which by either permanent or transient populations in can be found in the Alboran Sea and off the North areas where the influence of oceanic inflow i3 the African and Italian coasts to a latitude of Naples), greatest. However, the specific composition of the 3. "Oriental" species, abundant not only in the plankton of these two seas is very different since eastern part of the Mediterranean Basin but aiso the Mediterranean fauna originates from the in the Tyrrhenian Sea which is fed by the warmer Atlantic and the Red Sea fauna from the Indian and saltier waters from the east. They are rare Ocean. west of a line through Corsica and Sardinia which constitutes the border between the Eastern and Western Mediterranean water (e.g. Sagitta DEEP WATER PLANKTON serratodentata) and 4. "Boreal" species, In both seas, the deep water plankton is much namely Sagitta setosa whose southernmost limit in the northeast Atlantic is the Bay of sparser than in the adjacent oceans. The most Biscay. This boreal relict is abundant throughout probable explanation for this is the effects of the the northern sectors of the Mediterranean where very warm deep temperatures. In the Red Sea, the waters have low salinities and temperatures where the deep water temperatures ere 22*C, Wishner ( 1980) claims that most of the available i.e. Gulf of Lion, Ligurian Soa, Adriatic Soa, Aegean Sea and in the Black Sea. food is decomposed before it reaches the bottom; For the southern waters of the Red Sea several furthermore oxygen content is abnormally low. In -44- ; • - Sagitta enflata 35* UO'E • Pterosagitta draco /// Sagitta serratodentata (Médit.) VZ Sagitta pacifica ( Red See) Sagitta setosa Fig. 1. Distribution of some chaetognaths illustrating the four categories of distribution pattern. Boreal: Sagitta setosa ( Mediterranean only); ubiquitous: S.en flata; halophilic: S. serratodentata (Mediterraneèn) and S.pacifica (Red Sea); oceanic: Pterosagitta draco. Oceanic water currents are indicated by arrows. addition, at these temperatures, the metabolism of thd organisms is rapid and so their food requirements are higher. Nevertheless, In the Mediterranean there are a few bathypelagic occur as shallow as 200m. species such as the scyphomedusan Periphyllt The shallow sills at Gibraltar (300m) and periphylla, the mysfdecean Eucopia hanseni Hanish ( 100m) may be a barrier to the spread of and the decapod crustacean Gennadas elegans, many purely bathypelagic species (e.g. but none of these occur in the Red Sea. Sagitta Eukrohnia spp.), but many species do gain lyra, a meso-bathypelagic chaetognath species, access to the Mediterranean at some time in their lives in the Mediterranean but not in the Red Sea, lifecycle during ontogenetic, seasonal or diet although it Inhabits the Gulf of Aden where it mey vertical migration and the real barrier is the -45- change in hydrolog/ (Casanova, 1977). For greeter than its counterpart in the Gulf of Aden example, the chaetognath Sagitta planctonis is (Casanova, unpubl); this difference would not meso-bathypelagic in the Bay of Cadiz, but a few persist If there was free gene flow through the specimens, usually young, can be carried in by Strait. Similarly Beckmann (1984) concluded the Atlantic current during their diel migrations. from samples collected at a line of stations Once inside the Mediterranean, they are restricted running from the Gulf of Aden to the middle of the to the stream of Atlantic water (0-300m) and Red Sea that the copepod Haloptilus longi being unable to migrate back down to their normal cornis is a species rare in the Strait of bathymetric level they disappear quickly Bab-el-Mandeb; according to his data, it is a (Furnestin, 1970). This poses the problem of the "septentrional" species with populations from the fate of those oceanic organisms carried Into either Gulf of Aden and from the Red Sea avoiding the the Mediterranean or the Red See. Strait. FAUNISTIC RELATIONS WITH ADJACENT OCEANS CONCLUDING REMARKS It ha3 been known for some time that certain Thus fauniatic exchanges between the Atlontic species cannot survive in these nearly Ocean and Mediterranean See, and the Indian Ocean land-locked seas. Ruud ( 1936) claimed this to be and Red Sea appear only temporarily to enhance the case for Thysanoessa gregaria in the the populations close to the straits. Such Mediterranean and Stubbings (1938) correlated exchanges dn not have lasting effects since the new the numerous shells of pteropods on the southern immigrants neither survive nor interbreed with floor of the Red Sea to their death after entering the local population, at least for truly open-ocean the Erythreen zone. Recently, Beckmann (1984) species. Two lines of profitable lines of research described the sequence of changes ending in death can be suggested: which occur in the Copepod Eucalanus crassus 1. the study of copepods species occuring on both es it is carried into the Red Sea via the Strait of sides of the straits to investigate if there are Bab-el-Mandeb. morphological differences in tegumentary organs Thus oceanic species advected into the between the populations (cf. Fleminger, 1973). Mediterranean or the Red Sea disappear more or 2. assessment of the rate at which spéciation has less rapidly the farther they are carried In from taken place in the different species and plankton the ocean, depending on the varying strictness in groups, using thecosome shells (e.g. 12.000 their ecological requirements, but It Is generally years for Cavolinia innexa In the Western thought that in time the stock of species able to Mediterranean) to date the appearance of present adapt to conditions in these seas will become day species. Increasingly richer because of the continual Influx of animals from the ocean. However, there ara morphological differences REFERENCES between Atlantic and Mediterranean populations in thecosomes (Rampai, 1975) and decapod crustaceans (Casanova, 1977), and no specimens -BECKMANN, W., 1984. Mesozoopianklon distribution with intermediate characteristics hove been on a transect from the Gulf of Aden to the central Red Sea during the winter monsoon. Oceanol. Ada, 7 observed in the vicinity of Gibraltar where the (1): 87-102. oceanic and mediterranean populations Inter -BI6E10W, H. 8. & M. SEARS. 1937. Siphonophora. mingle, thus they appear to interact as separate Rep, dan. Oceangr. Exped. 1903-1910, species. Hedit. adj. seas, ! I, Biol.-: 1-144. Likewise, the amount of eye growth undergone -CASANOVA. J. P. 1977. La faune pélagique by the Red Soa population of the chaetognath profonde (Zooplancton et micronecton) de la Sagitta decipiens by sexual maturity is much Province at/anto-médilarranéenna. Aspects -46- taxonomique, biologique el zoogéographique. Oceangr. Exped. 1906-1910, Medit. adj. Thèse Doei. Etat. Univ. de Provence. Marseille: Seas. ff(6) : 1*66. 1-455. -SOLENIA, A., 1973. La production primaire -CASANOVA. J. P.. 1985. Les chaetognathes de la planctonique en Méditerranée. Essai de mise i jour. mer Rouge. Remarques morphologiques et biogéo Bull. Etude en commun de la Méditerranée, graphiques. Description de Sagitta erythraea sp.n. n' spécial 5. Monaco: 1-128. Comm. int. Mer Médit., 29è Congrès- Ass. -STUBBINGS, H. G.. 1938. Pteropoda. Sei. rep. plénière, Lucerne. 11-19 oct. 1984. John Murray Exped. 19JJ-JJ, J (2) : 15-33. -fENAUX, R. 1973. Appendicularia from Ute Indian -WEIKERT, H., 1980. On Ute plankton of Ute central Ocean. Ute Red Sea and Ute Persian Gulf. In: B. Red Soa. A first synopsis of results obtained from Ute Zeitzschel (ed.) Biofogy of the Indian Ocean. cruises Meseda I and Meseda II. In: Proc. Symp. Springer Verlag: 409-414. coastal marine Environm. Red Sea, 6uiF of -FLEMINGER, A., 1973. Pattern, number, variability Aden and tropica! Western Indian Ocean, and taxonomic significance of integumented organs Khartoum, J: 135-167. (sensilis and glandular pores) in Ute genus Eucalanus -WEIKERT, H., 1982. The vertical distribution of (Copepoda Calanoida). Fish. Bull.. U.S. 7! (4): zooplankton in relation Io habitat zones in Ute area of 965-1010. Ute Atlantic II Oeep, Central Red Sea. Mar. Eco!. -FURNESTIN. M. L. 1970. Chaetognathes des Prog. Ser., 8\ 129-143. campagnes du "Thor" (1908-1911) en Méditerranée -WISHNER, K. F., 1980. The biomass of deep-sea et en mer Noire. Dana Rep.. 79: 1-51. benthopelaglc plankton. Deep-Sea Res., 27 A : -FURNESTI^ M. L. & J. C. COOACCIONI, 1968. 203-216. Chaetognathes du nord-ouest de l'océan Indien (Golfe d'Aden, mer d’Arabie, Golfe d'Oman, Golfe Persique). Cah. O.R.S.T.O.M.. sér. Océanogr., 6 (I): 143-171. -GAUDY. R. 1985. Features and peculiarities of zooplankton communities from Ute western Medi terranean. In: M. Moreitou-Apostolopoulou & V. Kiortsis (eds.) Mediterranean Marine Eco systems. Plenum Puhi. Corpor. : 279-301. -GREZE, V. N. 1963. Zooplankton of Ute Ionian Soa. Okeanol.issled. 9 : 42-59. (in russian) -HALIM. Y., 1969. Plankton of Ute Red Sea. Oceanogr. mar. Bio!.. 7 \ 231-275. -HALIM, Y. 1984. Plankton of Ute Red Sea and Ute Arabian Gulf. Deep-Sea Res.. J/ A : 969-982. -JESPERSEN, P.. 1923. On Ute quantity of macroplankton in Ute Mediterranean and Ute Atlantic. Rep. dan. oceanogr. Exped. 1908-1910, Medit. adj. Seas, J(3): 1-17. -flORCOS, S. A.. 1970. Physical and chemical oceanography of Ute Red Sea. Oceanogr. mar. Biot., 6: 73-202. -RAMPAL. J., 1975. Les Thécosomes (Mollus ques pélagiques). Systématique et évolution. Ecologie et biogéographie méditerranéennes. Thèse Doct. Etat. Univ. de Provence, Marseille: 1-485. -RAO, T. S. S., 1979. Zoogeography of Ute Indian Ocean. In: S. van der Spoel B. A. C. Pierrol-Bulls (eds). Zoogeography and diversity of Plankton. Bunge scient. Puhi. Utrecht : 254-292. -RUUD, J. T„ 1936. Euphausiacea. Rep. den. -47- THE DEMOGRAPHIC ANO EVOLUTIONARY CONSEQUENCES OF PLANKTONIC DEVELOPMENT HAL CASWELL Woods Hole Oceanographic Institution, U.S.A. INTRODUCTION DEMOGRAPHIC TRADE-OFF MODELS Over half of ali marine invertebrate species have Models based on demographic trade-offs have been incorporated a planktonic larval stage into an studied by Vance (1973), Pechenik (1979), otherwise benthic life cycle (Thorson, 1950). Caswell ( 1981), Christiansen & Fencheli 1979), The biogeographic implications of this life history and others. The approach is to describe some pattern are profound (e.g. Scheltema, 1978; portion of the life cycle, to derive from it a Jablonski & Lutz, 1983). Species with long measure of fitness, to evaluate the sensitivity of planktonic larval stages tend to have greater fitness to changes in planktonic development, and geographical ranges and longer geological durat to conjecture that those changes which increase ions than those with restricted larval duration fitness will be those observed in nature. The (e.g. Scheltema, 1978; Jablonski, 1982 for data predictions of such models depend critically on the on gastropods). The relation of dispersal and gene choice of a measure of fitness and on the flow aiso has important implications for patterns inter-trait correlation pattern (Caswell, 1981). of local adaptation and spéciation (Scheltema, For example, consider the allocation of 1978). Hansen ( 1983), for example, finds that resources to larval provisioning. This problem tropical neogastropods with non-planktotrophic was examined by Vance (1973) 8S a way to development have exhibited greater spéciation distinguish planktotrophic (i.e. low level of rates than those with planktotrophic development, provisioning) and lecithotrophic ( i.e. high level presumably because the greater dispersal of provisioning) feeding behaviours. Assume that abilities of the latter make geographical isolation total development time T is fixed; it Is partitioned more difficult. into a non-feeding (e.g. lecithotrophic) stage of There is both inter- and intra-specific variat duration x and a feeding stage of duration T-x. The ion in planktonic development. This variation greater the degree of provisioning of the larva, raises the question of the selective factors that the larger the value of x. The probabilities P, and favor the incorporation of planktonic stages In an P2 of surviving the two stages are given by: otherwise benthic life cycle, and whether those P, =exp(-p,x) factors can explain geographical (e.g. the rarity of planktonic larvae In the Arctic) and environ P2 = exp[-p2(T-x)] mental (e.g. the rarity of planktonic larvae in the where Pj and p2 are the mor tality rates in the deep sea) patterns? two stages. The probability of surviving to This paper reviews three types of models which settlement is then histories, with a planktotrophic, feeding stage dW/ax = f(x) [F' (x) - (p,-p2)F (x)l following a lecithotrophic stage supported by The maxima and minima of W occur whenF' (x) = parental investment. On on Interspecific basis, (p,-p2)F(x), at which point aW/dx=0. When one would expect a continuous spectrum of life F(x) is concave dowward [F"(x)<0], a stable history types. On the other hand, when F(x) is maximum of W exists, with the optimal value of x concave upward [i.e. when F"(x) is sufficiently varying directly with (m2_M)) (Fig. ia). In this greater then zero], as In Vance (1973); see case, one would expect to find "mixed" life Caswell (1981), only the extreme values of x are stable (Fig.lb). In this case, only the extreme -F'(X) life history types ere stable, and one expects to see planktotrophic and lecithotrophic life cycles as discrete alternatives. In both cases, the relative mortalities In the two stages are important in determining the optimal strategy, but must be evaluated in relation to the constraint function. NICHE SHIFT MODELS Many species, including Uiuse under discussion here, utilize two distinct niches during their ontogeny. Istock ( 1967)(cf. Slade & Wasserburg, 1975; Wilbur, 1980; Istock, 1984) introduced the first model to consider the effects of shifts from one niche to another during development. However, this model incorporates little of the X X biology of the species in the two habitats, and is based on questionable assumptions (to me, at Fig. la Left: a concave downward cost function least) about the action of selection. relating fecundity (F) and the duration (x) of the A recent and very promising approach is that of first stage (e.g.) lecithotrophic of a larval life Werner & Gilliam ( I984X see Gilliam, 1982; cycle. Right: the Intersection of -F' (x) ar/i Werner, 1986). Their work Is directly concerned (po-pj) F(x) defines the optimal value o • with fish and amphibian life cycles, but has great indicated by Decreasing p2 or increasing p ( to potential application to marine Invertebrates. produce the dashed curve changes the optimal They consider a life cycle passing through two or value of x to x2. That is, as planktotrophic more distinct habitats.Each habitat is mortality decreases or lecithotrophic mortality characterized by two curves, which give the increases, the optimal life history spends less growth rete [g(x)l and mortality rates [p(x)l as time In the lecithotrophic stage. functions of size (x). The overall fitness (the lb Left: As in Fig.la, but now the cost Intrinsic rete of Increase) depends on the 3lze at function is concave upward. Right: As drawn in which the individual switches from one habitat to this exempla, (p2-pj) F(x) is always greater another. Depending on the details, it might be than -F‘(x). As a result, selection leads to an advantageous to sacrifice potential rapid growth in optimal value of x at the extreme x * T, producing a habitat with high mortality, or vice-verse. a life cycle without the second stage. If (p2-pj ) Gilliam (1982) shows that, for populations F(x) <-F'(x), selection results in x = 0, and the near equilibrium, and in which metamorphosis first stage disappears. Given such a cost function, occurs before sexual maturity, fitness is mixed life cycles are not possible. maximized by choosing the habitat which, at every -49- size x, minimizes the ratio p(x)/g(x). If density. Levin et al. ( 1984) have shown that the mortality is uniformly lower and growth higher ESS for the fraction of offspring dispersed (D) in In one habitat than the other, only that habitat such situations increases with the probability of should be utilized. If one habitat has a higher surviving dispersal («); D goes to one es «goes to mortality rete but aiso supports faster growth, one. Thus, if there were no cost to dispersal, the the shapes of the growth and mortality functions ESS 1s to disperse ali offspring. For small values can mandate a transition from one to the other at a of «, on the other hand, the ESS depends on the particular size. This model is a promising probability of extermination of local populations. approach to transitions which reflect trade-offs Unless this probability Is zero, the ESS for D is between growth rale and mortality, and should be positive (and usually quite large) even as «goes investigated in the context of planktonic larval to zero. Thus, given spatial variation and the stages. chance of local extinction, some degree of dispersal is always favored. Scenario 2. That environmental heterogeneity DISPERSAL MODELS can lead to selection for dispersal is not surprising. Hamilton & Mey (1977) and Comina One obvious consequence of planktonic et al. ( 1980), however, show that dispersal is development is dispersal. However, neither of the favoured even in a homogeneous environment. models considered so far has explicitly included They sssume a large set of identical patches, each the possible benefits of having offspring settle in supporting a limited number of adults. The different locations from parents. undispersed offspring of the local adults and the The analysis of dispersal strategies is offspring which settle in the patch compete for the complicated because the benefits of any given space in each generation. A sedentary strategy is strategy are frequency dependent, i.e. they depend not an ESS because an invading strategy with D>0 on the strategies adopted by the rest of the decreases its competition with itself and increases population. For example, suppose that a fraction D that with the sedentary strategy by dispersal. As of offspring disperse, while 1 -D do not. If a whole long 8s stochastic settlement patterns generate population hss adopted a sedentary strategy Inter-patch variance in genetic composition, ( D=0), a mutant with D>0 will be able to invade, there Is an advantage to dispersal. since it takes advantage of locations which the sedentary strategy leaves vacant. On the other hand, a mutant with D<1 can invade a population in which D= I, because the types which disperse CONCLUSIONS ali their offspring leave behind vacant sites in which a more sedentary type can flourish. An Each of these classes of models predicts the evolutionarily stable strategy (ESS) is one evolution of planktonic larval stages under some which, once adopted by the population, is proof circumstances. However, each does so for a against invasion by other strategies. It may not be different reason; the trade-off between offspring ''best" in the sense of maximizing any measure of number and provisioning, the trade-off between fitness, but it is the strategy which is expected to planktonic and benthic growth and mortality rates result from selection. and the advantages of dispersal in spreading the Hamilton & Mey (1977), Comina et al. competition for adult sites. Given the multiplicity (1980), and Levin et al. (1984) analyze ESS's of potential causes revealed by the models, it for dispersal In detail. The models are too complex seems unlikely that any single factor actually to discuss here, but their conclusions point to two determines the evolution of planktonic life cycles different situations which favour dispersal. in nature. The serious consideration of more Scenario 1. Consider an environment composed general models, including those developed by of many sites, varying in time and space because population biologists concerned with other types of abiotic variation and local differences in of organisms, would probably make a major -50- contribution to understanding planktonic life -SCHELTEMA. R., 1978. On the relationship between cycles. dispersal of pelagic veliger larvae and the evolution of marine prosobranch gastropods. In: B. Battaglia & J. A. Beardmore (eds) Marine organisms: ACKNOWLEDGEMENTS genetics, ecology and evolution. (Plenum. New York): 302-322. -SLADE. N. A. & R. J. WASSERBURG, 1975. On the The writing of this paper wss supported by NSF evolution of complex life cycles. Evolution, 29 : Grant BSR82-14583. Woods Hole Oceanographic 568-571. Institution Contribution 6091. -THORSON, G., 1950. Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev., 25 : 1-45. REFERENCES -VANCE, R. R.. 1973. On reproductive strategies in marine benthic invertebrates. Am. Nat. t07 : -CASWELL, H„ 1981. The evolution of ‘mixed’ life 339-351. histories in marine invertebrates and elsewhere. Am. -WERNER, E. E., in the press. Amphibian metamorph Nat., 117\ 529-536. osis: growth rale, predation risk and the optimal size -CHRISTIANSEN, F. B. & T. M. FENCHEL, 1979. Io transform. Am. Nat. Evolution of marine invertebrate reproductive -WERNER. E. E. 8, J. F. GILLI AM. 1984. The onto patterns. Theor. Pop. Bio!., 16 : 267-282. genetic niche and species interactions in -COMINS, H. H.. W. D. HAMILTON 8> R. M. MAY. 1980. size-structured populations. Ann. Rev. Ecoi. Evolutionary stable dispersa! strategies. J. Theor. Syei., 15: 393-425. Bio/., 82 : 205-230. -WILBUR, H. M., 1980. Complex life cycles. Ann. -GILLIAM, J. F.. 1982. Habitats usa ano Rev. Eco). Syei., II : 67-93. compel Hiva bottlenecks in size -str uctured fish populations. Ph.D. Thesis, Michigan Slate Univ.: 107pp. -HAMILTON, W. D. & R. M. MAY, 1977. Dispersal in stable habitats. Nature, 269: 578-581. -HANSEN, T. A.. 1983. Modes of larval development and rates of spéciation in early tertiary neogastropods. Sience, 220: 501-502. -ISTOCK. C. A.. 1967. The evolution of complex life cycle phenomena: an ecological perspective. Evolution, 21: 592-805. -ISTOCK, C. A., 1984. Boundaries Io life history variation and evolution. In: P. W. Price, C. N. Slobodchikoff & W. S. Gaud (eds) A new ecology: novoi approaches to interactive systems. Wiley. New York : 143-168. -JABLONSKI, D., 1982. Evolutionary rales and modes in late cretaceous gastrophlds: role of larval ecology. Proc. Third North Am. Paleontol. Conv., I : 257-262. -JABLONSKI. D. & R. A. LUTZ. 1983. Larval ecology of marine benthic invertebrates: paleobiological implications. Biol. Rev., 58: 21-89. -LEVIN, S. A., D. COHEN A. HASTINGS. 1984. Dispersal strategies in patchy environments. Theor. Pop. Biol., 26: 165-191. -PECHENIK. J. A., 1979. Role of encapsulation in Invertebrate life histories. Am. Nat., !M : 859-870. -51- ESTUARIES AS TRANSITIONAL ZONES WITH REFERENCE TO PLANKTON IN THE NEAR SHORE WATERS P.CHANDRA MOHAN Andhra University, Waltair, India. INTRODUCTION end of the brackish water zone, about 44 km from the mouth. The width of the river was 900m and The present investigation was carried out from the depth about 10m. Plankton sampling and November 1981 to June 1982 in one of the big determination of the surface temperature and river estuaries in south India ( 17*20' - 18‘00'N salinity were conducted during the day twice a & 81*31’ - 82‘20'E), the Godavari estuary, a month. A conical net, (50cm diameter) and normal type estuary in which due to river 143pm in mesh size, was towed vertically from a discharge salinities sre reduced, as one goes depth of about 5m. The displnement volumes were upstream (Emery & Stevenson, 1957). It measured and the abundance of the major zoo receives rain during SW and NE monsoons. The plankton species was estimeted (Fig. 1 ). maximum rete of discharge is about one and a half million cubic feet per second. It has three main branches namely, Gautami, Vasista end Vainateyam and has extensive backwaters with dense mangrove vegetation neer their outlets into the Bay of Bengal. Broadly three periods of water condition can be distinguished: the SW monsoon PIX A'.APAM ISIANO (,< period from July to September, during which the entire estuary is freshwater: a postmonsoon period from October-January when there is considerable sea water penetration into the estuary establishing clear vertical stratification of the water column end a premonsoon period from Fig. 1 Godov nr 1 Estuary with station locations February to June when typical marine features predominate and saline waters extend to 44 km TEMPERATURE above the mouth. In this latter period the upper Monthly mean temperature variations in surface reaches of the river dry up due to lack of water at station I ranged from 26*0 in January to freshwater flow. a maximum of-32.2*0 recorded in May. The temperatures were elwar/s highest between 14.00 and 15.00 hours, indicating the variation was METHODS caused by diel irradation, not by tides ( Table I A). The Godavari estuary has a semidiurnal tidal SALINITY cycle. The maximum range of tidal oscillation is The variation In salinity was governed by the 1.5m. In the entire stretch of 44km of the effect of tide and precipitation. During the estuarine area three stations were set for periodic monsoon period when the river is in spate the plankton sampling: station I, located near the entire estuarine area was fresh and highly turbid. mouth where the width of the river was 650m and Tongues of saline waters could be detected only the depth about 13m: station II, situated about 19 after October at station I, when penetration km from the mouth where the width W8s 1400m Intensifies and extends further into the upstream and about 10m depth: station III at the extreme area. At the heed of the estuary, Milne waters -52- Table I Monthly variations in the Godavari Estuary * A. Monthly mean surface temperatures ( *C) Nov. Dec. Jan. Feb. Mar. Apr. May June Station 1 25.80 25.50 25.00 26.20 29.80 30.30 32.20 31.50 Station II 26.70 25.43 25.16 26.32 28.96 30.93 32.10 31.00 Station III 25.00 25.80 26.10 27.80 30.00 31.50 33.00 30.00 B. Monthly mean surface salinities (°/oo) Station 1 14.24 23.50 26.17 28.05 32.54 33.33 34.31 31.00 Station II 5.61 10.22 14.60 20.70 26.63 29.31 29.34 27.00 Station III Fresh water 5.01 11.31 12.63 8.19 * C. Displacement volumes of zooplankton (ml/m3 ) Station 1 1.90 3.00 2.00 5.00 16.50 8.50 3.75 3.30 Station II 2.70 2.30 5.25 11.50 40.00 35.00 41.20 48.70 Station III * « » 2.00 8.00 9.00 4.00 « D. Abundance of zooplankton numbers/m3 Station 1 433 4230 1221 242 9375 4110 1310 3140 Station II 185 1181 2973 14357 5966 15760 4965 7130 Stagon III * * * 165 1200 900 400 t- * No sampling due to prevalence of freshwater conditions could be found only from February to June. morkedly high. Comparing stations I and III, to Maximum salinities were recorded during station number ii the latter had fairly stable summer (April -June) (Table IB). conditions for most of the year and therefore maintenance of populations seems possible here ZOOPLANKTON BIOMASS (Table I C. D). Zooplankton biomass showed a conspicuous peak in November-December whereas phytoplankton was PLANKTON SPECIES most abundant in March-April. Corresponding Hydromedusae, represented by Phialidium with the post-monsoon period organisms start to hemisphaericum, L triops tetraphylla, and enter the estuary from September onwards. The Bougainvillia fulva were present, almost early Immigrants were mostly euryhalina constantly, during the period of stud/- Copepods crustaceans. Later, with increasing salinity were very abundant, dominant species were: typical littoral groups become established in the Eucalanus elongatus, Paracalanus parvus, estuary. In March and April when stable Acrocalanus gracilis, Pseudodiaptomus hydrographical conditions prevailed, the 200- binghami, Labidocera acuta, Pontella plankton biomass and numerical abundance were fera, Acartia clausi, A. erythrea, -53- A. sewelli, Corycaeus speciosus, environment. Occasional migrants from the Macrosetella gracilis and Euterpina neritic waters were aiso seen in the estuaries acutifrons. Among the adult crustaceans myskis (Chandramohan, 1977). were seen in fairly high numbers in the samples The estuaries bordering the Bay of Bengal are collected at night. The common species peculiar in their ecological nature since they encountered were Rhopalophthalmus kempi, contain a rich variety of organisms and contribute Mesopodopsis orientalis, Gastrosaccus to the enrichment of populations in the near shore muticus end Potamomysis assimilis. area. They aiso transport large quantities of Except Tor L ucifer hanseni which was present nutrients downstreams towards the sea, during in large numbers for most of the year .ali decapod monsoon periods. crustaceans were in larval stage. Sagitta enflata and Sagitta robusta were common among chaetognathi Non-crustacean invertebrate REFERENCES larvae, 3een in the samples invluded members of Echinodermata, Mollusca, Brachiopoda and -ABBOTT. W. & C. E. DAWSON. 1971. Water end Polychaeta. Soon after the start of the monsoon due water pollution hand book. Clacdo, L.L. Marcel to large scale flooding of the rivers, the inshore Dekker Inc. N.Y. : 51-140. waters of the Bay of Bengal register a marked -CHANDRAMOHAN. P.. 1977. Seasonal distribution of drop in salinity to about !7°/oo (Genapati & copepods in the Godivari estuary. Proc. Symp. warmwater zooplankton, Spec. Publ. NIO Murthy, 1954). The migration of plankton (UNESCO) : 330-336. populations is facilitated by the regular sequence -CHANDRAMOHAN. P.. 19B3. Mysidacea of the of high tides which tends to carry these organisms Godivari estuary. Mahagasar- Bull. Natn Inst. from the nearshore area into the estuary. The Oceanogr., !6{3) : 395-397. extensive back waters near the mouth of the -EMERY. K. 0. 8, R. E. STEVENSON, Estuaries and Godavari River affords good shelter for many lagoons. 1. Physical and chemical characteristics. organisms during the flood season and prevent Geo!. Soc. Amor. Mem. 67( 1) : 673-750. them from being washed out of their normal -GANAPATI. P. N. & V. S. R. MURTHY. 1954. Salinity habitat. Panikkar (1951) studied the physiol and temperature variations of the surface waters off ogical adaptation of estuarine organisms and made the Visakhapatnem coast. Mem. Oceanogr. Andhra a note on the role of backwaters in maintaining Univ. 49: 125-142. stocks of planktonic forms, ss a refuge during -PANIKKAR, N. K. 1951. Physiological aspects of adaptation to estuarine conditions. Proc. unfavourable conditions. From the studies made /ndo-Pacif. Efsh. Counc. 1950, sect.3 : 168-175. (Chandramohan, 1983) on the biolog/ of the mysid Rhopalophthalmus kempi, It was obvious that the juveniles of this species enter the estuary during November from the backwaters, as this species Is not normally found in the inshore area. The same is observed for Potamomysis assimilis. Surely estuaries are more productive than adjoining bodies of freshwater or sea (Abbott & Dawson, 1971). Since there is a net seaward movement of water, most of the plankton with nutrient rich waters from the estuaries are pushed into the neritic zone, during flood season. Only fifteen species out of sixty copepod species recorded in the present study were endemic to the estuary inhabiting euryhaline areas. We found freshwater species from the upper regions and aiso neritic species entering the estuarine -34- L AT IT UDI N AL VARIATION IN DIVERSITY AND BIOMASS IN I KMT CATCHES FROM THE WESTERN INDIAN OCEAN D. M. COHEN Natural History Muaaua of Los Angeles County, U.S.A. INTRODUCTION (Fig. 1 ) of the R.V. ANTON BRUUN es part of the U.S. program in Biology of the International It Is widely stated that In general there are more Indian Oceen Expedition in 1963 and 1964 species of plants and animals at low latitudes than (narrative and final cruise reports containing at high and that biomass and/or productivity ara station data are presented In Anonymous 1964a, the Inverse of diversity (Fischer, 1964; Planca, 1965a for cruise 3 and Anonymous 1964b, 1966; Pielou, 1975;1979). The applicability of 1965b for cruise 6). Diversity is based on these hypotheses is examined with reference to species richness, numbers of midwater fish data derived from catches, particularly of species in each total catch and/or catch fraction; midwater fishes, taken by an IKMT during two limitations of the data prevent consideration of North-South transects in the western Indian species evenness. Semples were sorted in the Ocean. laboratory and examined by specialists who distinguished species classified in more than 35 families (data in the author's files) METHODS Sources of error include variable lengths of tows, unequal absolute species pools, unequal Collections were made during cruises 3 and 6 population densities, variable availability to gear, patchiness, catch contamination, Incomplete 40* 60° 80*E information on net time at various depths, variation in relative vessel speed during trawls, and Incompletely known taxonomy. RESULTS In this connection data are presented on numbers of species caught, biomass, primary productivity, and hydroghaphy. SPECIES DIVERSITY Latitudinal variation in absolute number of species caught is Illustrated in figure 2 A measure of diversity that takes into account fishing effort is number of species per hour, Illustrated In figure 3. Greatest diversity appears to occur between 7.5*N latitude and I2*S latitude for catches between the surface and 1000m and between the Fig. I IKMT stations occuptod during cruises 3 and surface and depths between the surface and 6 as part of the U.S. Pregram in Biology of the greater than 1000m, both dependent upon and International Indian Ocea.i Expedition. independent of fishing effort. Catches Independent -55- cf effort from the deep fraction of trawls fishing BIOMASS between the surface and depths greeter than Milliliters per hour cautfit of fishes snd 10OOm do not vary notably with latitude. invertebrates combined is illustrated in figure 4. For shallow tows a biomass peak occurs at 1.5* S latitude. Biomass tends to be low between 12' S latitude and and 23* S latitude. ‘ ° * MeJ Fig. 2 Numbers of species of midwater fishes caught during two north-south transects in the western Indian Ocean. Solid dots and squares connected by solid lines are catches between the surface and 1000m during cruises 3 and 6, respectively. Solid dots and squares connected by dashed lines are catches between the surface and Fig. 4 Volumes of midwater flslies and depths greeter than 1000m during cruises 3 and invertebrates combined expressed as milliliters 6, respectively. Open squares and circles are the per hour of trawling during two north-south deep fraction (a variety of depth intervals transects in the western Indian Ocecn. Dots and between 150-3500m) of trawls fishing between squares connected by solid lines are catches the surface and depths greater than 1000m during between the surface and 1000m during cruises 3 cruises 3 and 6, respectively. and 6, respectively. Dots and squares connected by dashed lines are catches between the surface and tyir depths greater than 1000m during cruises 3 and 6, respectively. PRIMARY PRODUCTIVITY Data on primary productivity during seven NOE cruises (Including 3 and 6) of the ANTON BRUUN in the western Indian Ocean have been presented V by Ryther et al. (1966) from whom figure 5 of this paper Is taken. Along the tracks of cruises 3 and 6, productivity is generally higher in the north, decreases to minimal amounts between Fig. 3 Numbers of species of midwater fishes about 15*S latitude and 27*0 latitude, and then caught per hour of trawling during two north- increases slightly. south transects in the western Indian Ocean. Dots and squares connected by solid lines are catches HYDROGRAPHY between the surface and 1000m during cruises 3 Seversi water masses were sampled at the various and 6, respectively. Dots and squares connected by depths fished along the cruise tracks dashed lines are catches between the surface and (Wyrtki,1973). Surface water may be depths greeter than 1000m on cruises 3 and 6, discounted, as epipelagic forms are excluded from respectively. this analysis and midwater fishes taken from -56- W>° 60° 80° E literature) are listed in Table I. It is unlikely that any are mutually exclusive. Correlates, positive or negative, are not necessarily causes but may contribute to maintenance. Knowledge about the biology of midwater fishes in general and limitations of the present data in particular preclude consideration of ali the listed factors, but some can be addressed. In general, mid-depths diversity and biomass are intermediate in the north with high productivity; a seasonally changing regime of monsoon winds (northeast in the winter; southwest In the summer) drives secondary variation In the pelagic environment; the deeper fauna, little influenced by the monsoons, lives in a more constant environment. Diversity 8t mid-depths is highest in equatorial waters, although somewhat offset to the south of the Equator, coinciding with the South Equatorial Current and the interface between Equatorial and Central water masses (hydrothermal front of «MO 0.11-025 0 26-050 051-1 00 >100 Wyrtki, 1973), which is characterized in part by a shallow thermocline. In an interesting paper Fig. 5 Chart of the western Indian Ocean showing on seabird distribution in the Indian Ocean, the positions of océanographie stations occupied Pocklington (1979) found highest bird diversity during Anton Bruun Cruises 2, 3, 4 A, 5, 6, 7, over the same area, with a similar pattern for and 8 and the general level of primary organic certain Copepoda, euphausi1d3, and flying fishes, production (Fig. 1 from Ryther et al., 1966). as well as highest albacore and yellowfin tuna abundance. He Interprets his data in the light of environmental stability. But lowest diversity and surface layers during the night reside by day in biomass for midwater fishes occurred in low deeper waters. From the northern ends of the variability, high predictability Central water transects to 8* - 1O'S latitude shallow tows wera which has very low productivity and a deep mainly in North Indian High-Salinity thermocline. Diversity in very deep water did not Intermediate water of complex seasonal origin vary notably with latitude; both in the north and (Wyrtki, 1973). Deep tows throughoi.it the south this faufia is in a stable and predictable transects fished partly in Deep water. South of environment; although early life historv stages of about 10'S to about 40*5 at the Subtropical some deepwater species pass time at shallower Convergence shallow tows in the great subtropical depths. Biomass, but not species diversity antlcyclonic gyre that has aiso been called the increeses at the far southern ends of the Indian Central water mass. At the far southern transects, where the environment becomes less ends of the transects several stations were taken stable and the thermocline shoals. in the Subtropical Convergence. With reference to table I, the environment Is physically partitioned horizontally and vertically by density (defined with the temperature-salinity DISCUSSION relationship) and vertically by temperature (as it relates to thermocline formation). The origins Some possible causes, maintained, and correlates of these physical boundaries might have served as of diversity (from an axtenslve sampling of the vicariaat events and possibly date from the -57- Table I Some possible causes and correlates of species diversity taken from the literature. Various combinations are not included. FACTOR CAUSE CORRELATE Recruitment rete + (spéciation* immigration-extinction) Number of niches + Niche size partitioning + ♦ Ecosystem complexity * + Stabi 1 ity-predictabi Ifty ♦ + Time ♦ ♦ Arae ♦ + Selection ♦ + Com potion ♦ ♦ Predation ♦ + Sympatric spéciation + Energy ♦ ? Latitude + Temperature + Productivity + Population equilibrium + mid-Miocene (van Andoi, 1976) in the present (Wiley & Brooks, 1982) to explain the diversity western Indian Ocean. Biological partitioning of of the midwater ichthyofauna. the physically partitioned midwater environment The marine latitudinal diversity gradient es an is indicated by many and diverse species expression of a species area curve has been behaviors with some species resident above the proposed by Schopf et al. ( 1977); however well thermocline, some resident in it or below it, this explanation may serve for nearshore some migrating to it or through it, some environments, it does not explain diversity in the non-migratory, with variation in many individual midwater fish fauna, which occupies the most species patterns related to size, sex, season and space of any in the world but is the least diverse other variables. The vertical distribution of (Cohen, 1970; Horn, 1972). temperatures in the oceans wæ apparently Productivity may be In some Instances a important for spéciation in post times (Lipps, significant correlate, but it is not on its own a 1970), as it is today (Angel, 1968). A growing cause. literature on many aspects of midwater fish An attractive explanation is that of Huston biology including space sharing (Bedcock, 1970; (1979). Within limits, competitive dis Clarke, 1978; Ramella & Olbbs.1977; Legrand equilibrium of populations (which may be driven et al., 1972; Merrett & Rœ, 1974 and Peercy, by a variety of causes, in the present instance 1964 are only a few examples) contains inform physical disturbances in the northern Indian ation that can be used to define niches, and several Ocean) promotes disequilibrium of these attempts hove been made to do so formally. It populations, which inhibits competive exclusion seems likely that classical niche theory will go and thereby maintains high diversity. The far towards explaining midwater fish diversity environment in the southern gyre Is stable and distribution patterns making it unnecessary allowing a closer approach to population equi to invoke sympatrie spéciation or energy states librium, which allows competitive exclusion and -50- lessens diversity. A situation that is quite to the -ANONYMOUS, 1964b. Narrative report: Anton Bruun contrary and not easily explained has been cruise 6. U. S. Program in Biology International Indian described for the highly diverse plankton Ocean Expedition. Woods Hoia Oceanogr. Inst., community living in the central gyre of the North News Bull., 8\ 9 pp. Pacific Ocean, an old and stable mass of water -ANONYMOUS. 1965a. Final cruise report Anton (McGowan & Walker, 1985 and papers cited Bruun Cruise 3. Oceanographic data, therein). Diversity in plankton and in midwater bathythermograph positions, station lists, for biological collections. U.S. Program in Biology fishes may be determined and maintained by International Indian Ocean Expedition. Woods Hole different causes. Oceanogr. Inst., : 53 pp. It is premature to speculate further on the -ANONYMOUS. 1965b. Final cruise report Anton signifiance of interactions of various of the Bruun cruise 6. Oceanographic data, tabulated factors. Multi-species-environment bathythermograph postions, station lists, Tor models constructed by fishery biologists are far biological collections. U.S. Program in Biology from perfection, notwithstanding relatively few International Indian Ocean Expedition. Woods Hoia species and relatively large data bases. Oceanogr. Inst., : 70 pp. Comparable knowledge of the midwater fish -BADCOCK, J., 1970. The vertica! distribution of community is in an even more primitive mesopelagic fishes collected on the SOND cruise. J. condition. mar. bio/. Ass. U.K., 50'. 1001-1044. -CLARKE. T. A.. 1978. Die! feeding patterns of 16 In summary, midwater fishes in the Indian species of mesopelagic fishes from Hawaiian waters. Ocean do demonstrate higher diversity at low Fish. Bull., 76{3): 495-513. latitudes, but the overall pattern is modified by -COHEN, 0. M„ 1970. How many Recent fishes are the physical and chemical regime. Isolation and there? Proc. Calif. Acad. Sei. (4th Ser.), 36 niche diversification, suggested by Marshall (17): 341-346. (1963) are possible causes. Competitive dis -FISCHER, A. G„ 1960. Latidudinal variations in equilibrium of populations deserves further organic diversity. Evolution, I4( 1): 64-81. investigation. The latitude-diversity-biomass -HORN, M. H., 1972. The amount of space available relationship is not clesr. for marine and freshwater fishes, fish. Bull., 70 (4): 1295-1297. -HUSTON. M., 1979. A general hyphothesls of species ACKNOWLEDMENTS diversity. Am. Nat.,//3( 1): 81-101. -KARALLA, C. & R. H. GIBBS. Jr.. 1977. The lanternfish Lobianchia dofleini: an example of the I thank my fellow principal investigators on importance oflife-hlstory information In prediction of cruises 3 and 6 of the ANTON BRUUN, R. Backus, oceanic sound scattering. In: NR. Andersen & A. Ebeling, R. Oibbs and G. Meed, as well as many B.JTahuranec (eds.), Oceanic Sound Scattering others who participated in field work and provided Prediction. Plenum Press : 361-379. Identifications. C. Ramella and J. Paxton helped to -LE6AN0, M. P., P. BOURRET, P. FOURMANOiR, R. organize data. I thank A. Cohen, A. Jahn, and J. GRANDPERRIN, J. A. GUEREDRAT, A. MICHEL. P. McGowan for their comments on the manuscript; RANCUREL, R. REPELIN & C. ROGER. 1972. Relations although, responsibility for it is mine alone. trophiques et distributions verticales en milieu pélagigue dans l'Océan Pacifique intertropical. Cah. O.R.S. T.O.H, (Oceanogr.), IO'. 303-393. -LIPPS, J.H., 1970. Plankton evolution. Evolution, REFERENCES 24{ 1 ): 1-21. -MARSHALL, N. B.. 1963. Diversity, distribution and -ANGEL, M. V., 1960. The thermocline es en spéciation of deep-sea fishes. Syei. Asa. Puhi. 5: ecological boundary. Sarsia. 34 \ 299-312. 1B1-195. -ANONYMOUS, 1964a. Narrative report: Anton Bruun -MCGOWAN, J. A. & P. W. WALKER. 1985. Dominance cruise 3. U.S. Program in Biology International Indian and diversity malntance in an oceanic ecosystem. Ocean Expedition. Woods Hole Oceanogr. Inst., Eco!. Monogr.. 55(1): 103-118. News Bull., 4\ 11 pp. -MERRETT. N. R. 8, H. S. J. ROE, 1974. Patterns and -59- seleclivily in the feeding of certain mesopelagic fishes. Mar. Bio!.. 26: 115-126. -PEARCY, W. 6., 1964. Some distributional features of mesopelagic fishes off Oregon. J. mar. Res., 22 (1): 83-102. -PIANKA, E. R.. 1966. Latitudinal gradients in species diversity: a review of concepts. Am. Nat., tOO (910): 33-46. -PIELOU, E.C., 1975. Ecological Diversity. John Wiley & Sons : 165pp. -PIELOU, E. C.. 1979. Biogeography. John Wiley & Sons : 351pp. -POCKLINGTON, R., 1979 An oceanographic Interpretation of seabird distributions in the Indian Ocean. Mar. Biol. SI: 9-21. -RYTHER, J. H., J. R. HALL, A. K. PEASE. A. BAKUN & M. M. JONES, 1966. Primary organic production in relation Io the chemistry and hydrography of the western Indian Ocean. Limnol. Oceanogr., II : 371-380. -SCHOPf, T. J. M.. J. B. FISHER. & C. A. F. SMITH III. 1977. Is the marine latitudinal diversity gradient merely another example of the species area curve? In: B.BaLtaglla 6» J.A.Beardmore (eds.), Marine Organisms- Genetics. Ecology and Evolution. Plenum Press : 365-386. -VANANOEL, T.H., 1976. An select overview of plate tectonics, paleogeography, and paleoceanography. In: J. Gray &> A. J. Boucot (eds). Historical biogeography, plate tectonics, and the changing environment. Proc. Thirty-seventh ann. Biol. Colloquium Sei. Pap. Oregon State Univ. Press : 9-25. -WILEY, E. 0. & D. R. BROOKS. 1982. A nonequilibrium approach Io evolution. Syei. Tool., 31: 1-24. -WYRTKI, K„ 1973. Physical oceanography of the Indian Ocean. In: B. Zeitzsci.ül (ed.), The Biology ot the Indian Ocean. Ecological Studies 3. Springer-Verlag: 18-36. 00- THE ROLE OF THE LEEUWIN CURRENT IN THE LIFE CYCLES OF SEVERAL MARINE CREATURES G. CRESSWELL CSIRO Division of Oceanography, Tasmania, Australia. INTRODUCTION turns to the eest with part of it spreading across the continental shelf. It hss a distinct offshore Are the life histories of pelagic creatures adapted front of several degrees Celsius and there its to ocean dynamics? To address this question the 3peedcan exceed 1.5 m.s- Farther eastward its description of a current system having distinctive passage across the Great Australian Bight is at a spatial and temporal characteristics was chosen to lower speed and not confined to the continental serve es 8 framework upon which to arrange the shelf. The overall progression of the Leeuwin patterns of behaviour of several pelagic forms. Current waters is not rapid because of the form Are there, for example, regions of correspondence ation of eddies and because of variations in flow in space and time to reveal that creatures match rate. Satellite drifter data suggest that the fastest their activities to the properties of a current transits from North West Cape to Cape Leeuwin system? and then across the Bight are roughly 60 and 90 days respectively. THE LEEUWIN CURRENT THE PELAGIC SPECIES The Leeuwin Current (Fig. I ) has its source in the warm, low-salinity tropical waters off THUNNUS MACCOYII northwestern Australia and seasonally flows Shlngu (1967,1978) pointed out that the southward past western Australia and then members of a species select their environment eastward across the Great Australian Bight according to their size and maturity. Juvenile (Cresswell & Golding, 1980; Legeckls & southern bluefin tuna prefer surface waters and, Cresswall, 1981). The Current frequently after spawning from September to March in the interacts with offshore eddies and the resultant "Oka" fishing ground northwest of Australia, they mixing produces a progressive decrease in its move southward along the western coast of temperature end increase in its salinity along its Australia to the Albany fishing ground. The path. distribution of larvae obtained on a recent survey On its southward passage the Current is confined of the "Oka" ground by the Fishing Agency of Japan io the upper two hundred metres and flows above is shown in figure 2. Comparing this distribution the continental slope with excursions onto the with figure 1 shows that the "Oka" ground lies continental shelf. Its existence W8s first inferred within the source region for both the Leeuwin and by Saville-Kent (1897) from the tropical South Equatorial Currents. marine fauna and warm waters that he The Leeuwin Current could provide the encountered at the Abrolhos Islands (28*30'- reference frame and transport medium for the 29*5). Other biological evidence Tor the Current young fish 8s they migrate from the "Oka" was summarized by Maxwell and Cresswell spawning ground down to Albany. Inflow of the (1981). It reaches the latitude of Perth, 32*S, in water and the juveniles into the Leeuwin Current late April (autumn) and can be detected there by could be expected to start in February. The its warm, low-salinity waters generally until arrival at Albany should be around May/June. October (spring). As it approaches Cape Leeuwin Fish in their first and second years are caught off ft commonly accelerates to I m.s-' end then Albany in May/June with the smallest recorded -61- Australia Perth ape Leeuwin 110°E Fig. I A schematic picture of the Leeuwin Current drawn from information collected by research vessels, satellite tracked drifters, and satellite infrared sensors. The current has Its source off northwestern Australia and consists of a shallow stream that is warmer and less saline than the surrounding waters. It mixes into eddies along its path and this leads to a progressive decrease in temperature and Increase in salinity. The region off northwestern Australia aiso serves es a source for the South Equatorial Current. fish (31.8 cm.) caught on March 25, 1951 ARRIPIS TRUTTA (Serventy 1956), perhaps the result of an The western subspecies, Arripis trutta esper unusually early Leeuwin Current. The young fish Whitley, ranges from southwestern Australia to ma/ sta/ in the Albany region because of the southern Tasmania (Malcolm, 1960). In a pre availability of a food source which Serventy spawning phase the adults migrate westward (Fig. (1956) reported was mainly the pilchard 3) travelling very close inshore. They era heavily ( Sardinops neopilchards). The Leeuwin fished by beach netting. Malcolm concluded that Current can serve to transport young tuna east their spawning occurred in the Geographe Bay ward on the next step of their migration: they are area in April and Mb/ because fully ripe fish were found off South Australia In their second and third only found in that area and because the western years. Their decrease in numbers en route ma/ be migration appeared to terminate there. Munro by losses into eddies offshore. (1963) found that the eggs hatched in a little -62- 115 120 125 E • 50-99 • • • • 5-19 • • • • • • Fig. 2 The distribution of southern blueffn tuna larvae in the "Oka" fishing ground from October to December, 1983. The data combine b?»h surface and subsurface tows of 20 minuta duration. (Reproduced from Fig. 12 of Fishing Agency of Japan, 1984.). under 40 hours. The spawning, either fortuit ously or by plan, is synchronized to the arrival of the Leeuwin Current and this would then take the larvae and juveniles eastward. The progression of the creatures to the eastern side of the Bight could take only 90 days if they remained in the waters of the Leeuwin Current. One year old fish are found as far east as Tasmania. The adult salmon Fig. 3 The pre-spawning westward migration of return eastward after spawning (Fig. 4) and give salmon as indicated by tagging. Only movements of rise to a second fishing season in the Albany 25 miles or more are shown. The numbers denote region. the recaptures at each locality. (Reproduced from Fig. 12 of Maruim, 1960). ARRIPIS GEORGIANUS The time and location of spawning of this species the larvae were widely distributed offshore, few, is similar to that of the Arripis trutta esper if any, larvae remained on or neer the continental Whitley. The spawning takes place north of Cape shelf from April to September. This period Leeuwin from February through June and so these corresponds to the time when the Leeuwin Current larvae, too, will be carried off by the Leeuwin flows southward intruding between the coest and Current in the direction of South Australia where the high salinity waters farther offshore. one and two year olds are found ( Malcolm, 1973). Rochford (1968) reported that larvae wera salinity-dependent in their distribution: they PANULIRUS LONGPIPUS CYGNUS were absent in waters of salinity less than 35.45 The eggs of this species hatch from November to °/ooS, such as found in the Leeuwin Current, and March along the western coast of Australia they were most abundant where the salinity was between North West Cepe and Cape Naturaliste 35.80-35.85 °/ooS. A year in which the Leeuwin (Phillips, 198t). The larvae rapidly disperse Current continues to flow through into the normal offshore, possibly due to wind-driven surface settlement period could result in a failure of currents. Studies in 1976 showed that, although lervoe to return to the coastal nursery areas. -63- 115 120 125 E they ere carried there by the Leeuwin Current. The migration of the western rock lobster (Panuluris longpipes cygnus) is likely to be interrupted by the Leeuwin Current. REFERENCES -CRESSWELL. G. R. * T. J. GOLDING. 1980. Observ ations of a south-flowing current in the southeastern Indian Ocean. Deep-Sea Res., 27A : 449-466. -FISHING AGENCY OF JAPAN. 1984. Report on 1983 research cruise of the R/V Shoyo-Maru : 104pp. -LEGECKIS. R. & G. R. CRESSWELL. 1981. Satellite observations of sea surface temperature fronts off the coast of western and southern Australia. Deep- Sea Res.. 28 k : 297-306. -MALCOLM, W. B., 1960. Area of distribution, and movement of the western subspecies of the Australian ’Salmon", Arripis trutta esper Whitley. Aust. J. mar. freshw. Res.. it: 282-325. -MALCOLM, W. B., 1973. An outline of the biology of the Ruff - Arripis georgianus (Cuvier and Valen ciennes). In: D. A. Hancock (ed.), Proc. Western Fish. Res. Comm, scient. Workshop Salmon Herrings : 9-17 -MAXWELL. J. G. H. & G. R. CRESSWELL. 1981. Dispersal of tropical marine fauna to the Great Australian Bight by the Leeuwin Current. Aust. J. Fig. 4 The post-spawning eastward migration of mar. freshw. Ros., 32: 493-500. salmon 83 indicated by tagging. The numbers -MUNRO. I. S. R.. 1963. Salmon egg survey in denote recaptures at each locality. (Reproduced Western Australia 1963. Dept. Fish. Fauna, from Fig. 13 of Malcolm, 1960). western Fish. Ros. Comm. Rep.. Perth. Document IO: IBpp. -PHILLIPS. B. F.. 1981. The circulation of the SUMMARY southeastern Indian Ocean and the planktonic life of the western rock lobster. Oceanogr. mar. Bioi. The southern bluefin tuna (Thunnus maccoyii) Ann. Rev. !9: 11-39. may be adopted to spawn at a time that releases -RWHFCRD. D. J.. 1968. The seasonal interchange of their young into the source waters of the Leeuwin water masses and the distribution of crayfish larvae and South Equatorial Currents. In the case of the (Panulirus cygnus) off south-west Australia. Dept. Leeuwin Current the young fish are carried in its Fish. Fauna, western Fish. Res. Comm. Rep., warm waters, down to the Albany fishing grounds Perth, Document 8: 18pp. where they reside up to one year before moving -SAVILLE-KENT. W., 1897. ■The, naturaliste in eastward, possibly aiso in the Leeuwin Current. Australia.' Chapman and Hall. London : 302pp. -SERVENTY, D. L., 1956. The southern bluefin luna, Spawning of the Australian salmon and herring Thunnus thynnus? maccoyii (Castelnau) in Australian (Arripis trutta and A.georgianus) may be adapted waters. Aust. J. mar. freshw. Ros., 7: 1-43. to place their young off southwestern Australia -SHINGU. C.. 1967. Distribution and migration of the just prior to the arrival of the Leeuwin Current. southern bluefin tuna. Rep. Nankai reg. Fish. The presence of one year old fish on the eastern Ros. Lab., 25: 19-35. side of the Great Australian Bight suggests that -SHINGU, C., 1978. Ecology and stock of southern -64- bluefln tuna. Japan Association of Fishery Resources Protection. Fish. Study No. 31. (English translation: Hintze. M. A., 1960. Aust. CSIRO Div. Fish. Oceanogr. Rep. Ul :79pp. -65- LIFE CYCLE STRATEGIES OF OCEANIC DINOFLAGELLATES BARRIE DALE Department of Beology, University of Oslo, Norway INTRODUCTION observing oceanic dinoflagellates, for the first time allowing consideration of their life cycle Biologists have long recognized the importance of strategies. dlnoflagellates es major primary producers In the oceans. Nrw there is increasing awareness that dinoflagellates are responsible for toxicity LIFE CYCLES IN FRESHWATER AND NERITIC seriously threatening public health and commerc DINOFLAGELLATES ial fisheries (e.g. Anderson, White & Baden, 1986). Details on life histories of freshwater and neritic Meanwhile, dinoflagellate studies have become dinoflagellates have been summarized (Dale, established as an important research field in 1983; Walker, 1985) and will not be repeoted paleontology over the past 25 years. Fossil dino- hera Although based on comparatively few flagellates have proved particularly useful in observations these details suggest the generalized biostratigraphy and they are now one of the most life cycle illustrated in figure 1, in which both important groups of microfossils used routinely asexual and sexual phssesere recognized It should in oil exploration. Both biological and be noted that this represents the free-living paleontological interests in the group have dinoflagellates; comparable information for concentrated on life histories since the benthic, symbiotic, and parasitic forms is scarce realization, in the early 1960's, that it is the and outside the scope of this paper. non-motile resting cysts in the lifecycle (see Fig. 1 ) that fossilize (e.g. Dale, 1983). ASEXUAL LIFE CYCLE Biogeography is an aspect of dinoflagellate Under optimal conditions dinoflagellates repro studies of increasing interest for biologists and duce asexually by simple binary fission. Depend paleontologists. Biologists are concerned with ing on the species and the environmental factors regulating the distribution of toxic conditions, division may occur every 1-15 days. species, and reports suggesting that certain of To withstand temporary adverse conditions (e.g. these toxic phenomena may be spreading to rapid shifts in temperature) cells may shed hitherto unaffected areas of the world (Dale & flagella and thecae to form non-motile cells Yentech, 1978) have introduced an element of referred to hero as temporary cysts. Character urgency in biogeographical studies. Paleontol istically these form rapidly (within a few ogists are interested in the biogeographical minutes to a few hours) and are of a more limited distribution of living dinoflagellate cysts es a duration (probably days rather than months) model for interpreting paleobiogeogrephy and compared with resting cysts produced in the paleoenvironments from the enormous amount af sexual phase (taking deys to form and able to data accumulating from the fossil record. survive for years). Laboratory cultures are essential for detailed life history studies, but until recently only e few SEXUAL LIFE HISTORY freshwater end neritic species had been cultured; For a long time sexual phases in dinoflagellates information concerning oceanic species was were not generally recognized, but it is becoming restricted to traditional plankton studies. This increasingly evident that sexual phases ara paper results from new methods of culturing and probably much more widespread than previously -06- Fig. 1 Schematic diagram of basic dinoflagellate life cycles based on 20 freshwater and neritic species (modifiedfrom Dale, 1983; Walker, 1985). asexual phase with motile, planktonic vegetative cell ( 1) dividing by binary fission ( IO) and sometimes forming non-mottle temporary cysts (ID to withstand environmental change. B« sexual phase with motile planktonic vegetative stage ( 1 ), producing gametes ( 2) pairs of which fuse to give planozygote (3). This eventually ( 3a) produces planktonic vegetative stage by reduction division ( 9) or loses motility and cyst formation begins ( 4) and may proceed ( 5) by expansion of cyst, producing resting cyst (hypnozygote) (6). Excystment (7) may produce a planozygote (8h), comparable with (3), which by reduction division (9) reestablishes planktonic vegetative stage ( 1), or in other species (8a) the reduction division Is completed during encystment, allowing direct establishment of stage(l)- considered. That so far such phases have been motile zygote (planozygote) (Fig. I). The piano- documented from only 23 species is thought to zygote may develop in two different weys. In some reflect the difficulties of inducing the sexual life species the planozygote undergoes meiosis cycle In cultures and the painstaking demands of producing the normal planktonic dinoflagellate observing these in natural populations. (3a In Fig. 1)- Although'such planazygotes may Known sexual cycles include gamete production, characteristically have a somewhat larger size, and ultimate fusion of pairs of these to produce a double longitudinal flagella, darker colour, and -67- large Intercalary bands they often remain "dispersed". They may thus help to extend a unnoticed In routine microscopic observations. In species range through Invasion of new territory other species the planozygote loses motility and by dispersed cysts that later establish e motile forms a resting cyst (hypnozygote), packed with population. Other stages in the lifecycle aiso may food storage products such es starch and lipids, be dispersed this way, but the greater resilience and often enclosed in a special resistant cell wall of cysts make them ideally suited to certain types (3b-6 in Fig. 1). It is these resistant cyst walls of long transport and dispersal. Of particular that form the dinoflagellate fossil record. A few concern to the problem of toxic species is the living cysts have been described with calcareous possibility that human agents may contribute to cyst walls (most likely celcite), end a group of this type of dispersal, for example through ships fossil cysts with siliceous walls is known from (ballast, bilge water, on the hull, sediment on Eocene sediments, but the majority of known dredging gear) and through transplanted shellfish. living cysts have nonmineralized walls that may be strengthened by sporopollenin-like material (a unique class of biopolymers formed from RECENT ADVANCES IN OCEANIC DINOFLAGELLATE carotenoids and/or carotenoid esters). STUDIES Paleontologists are especially interested to see LIFECYCLE STRATEGIES whether cysts, comparable to those routinely produced by freshwater and neritic dino "Life cycle strategy" is here used to denote the flagellates, ere produced by oceanic forms, complex inter reactions between life cycles and thereby suggesting the potential for an oceanic environments that ellow the individual (and fossil record in deep see sediments. thereby the species) to survive. Within the basic To many workers this seemed an unlikely life cycles summarized in figure 1, resting cysts possibility, but resting cysts clearly represent offer at least three functions that are important only one of two alternative strategies, end one that for survival strategies: protection, propagation, seems most suited to seasonally changing and dispersion. environments on a scale not considered typical for In temperate regions the "protective" role Is the pelagic realm. Furthermore, available illustrated by some species producing resting evidence suggests that even within neritic cysts that routinely overwinter at low temper dinoflagellates exposed to the large seasonal atures which the motile cells cannot tolerate. The changes of temperate regions, less than 50X of normal overwintering phase may last for up to IO the species produce resting cysts. Oele ( 1976) months (e.g. the warmer water element of found 26 cyst types in bottom sediments from a summer plankton In Norwegian fjords), and cysts Norwegian fjord where 57 species of motile ere able to survive at low temperatures for many dinoflagellates were recorded In long term years if not returned to conditions favourable for plankton records. Most species ere generally the motile stages. This aiso illustrates the presumed to survive extensive periods of "propagative" value of cysts acting es seeds; a unfavourable conditions by a few vegetative cells resting period and dormancy ensures that a new providing a residual population (eg. temperate end plankton population can be established during boreal lakes in winter), and this would seem a favourable intervals in a fluctuating environment. more likely strategy for oceanic species. Walker In this way species may extend their ranges (1985) suggested that oceanic species, in beyond the climatic boundaries in which motiles particular, may not have a sexual phase or may alone could survive year round. have en abbreviated sexual phase which lacks a Cysts generally function es benthic resting hypnozygote ( resting cyst). stages in freshwater and neritic waters, but es Nevertheless, Wall et al. (1977) classified "fine silt particles" they presumably are several cyst types es oceanic, based on their sometimes transported by currents and distribution iri bottom sediments from a series of -60- tronsects spanning coasta) to deep sea environments. These cysts were found almost exclusively from the outer shelf to the deep see, increasing es a proportion of the total assemblage seewards into abyssal depths. The suggested presence of oceanic dinoflagellate resting cysts raised important questions biologically. These concern the function and strategy of cysts in the life cycles of oceanic dinoflagellates. Geologically, the main questions concern which types of cysts are produced, in what amounts, their degree of preservability, and their ultimate contribution to the sediment flux. Traditional biological and geological studies were inadequate to investigate these questions. However, Improved culturing methods have produced the first cultures of oceanic species (Tangen et al., 1982), and large sediment traps placed at different depths In the deep sea provided the first opportunity to sample living cysts and other stages sedimenting out through the deep sea Fig. 2 Schematic diagram of part of the asexual water column ( Dale, in the press). phase In the life cycle of Thoracosphaera heimii (redrawn from Tangen et al., 1982). The uninuclear, non-motile vegetative stags, OBSERVATIONS ON THE LIFE CYCLE OF enclosed in calcareous shell ( t ) becomes THORACOSPHAERA HEIMII binucleer (2), emerges from the calcisphere One of the first oceanic forms to be studied in through opening (pylome) (3), divides (4) to culture was Thoracosphaera /te/>77//( Tangen give two cells (5) that quickly produces eta!., 1982). This species is commonly recorded calcareous shells (6). The Whoia sequence was from plankton in most oceans as distinctly small completed in about IO mins in laboratory (10-25pm diameter), spherical, non-motile cultures. cells that are enclosed in a relatively massive calcareous wall. Most biologists have classified Comparison of the asexual division phase Io Thoracosphaera together with coccolltho- Thoracosphaera (Fig. 2) with its equivalent phorids, whereas micropaleontologists have phase In other dinoflagellates (A In Fig. 1 ) shows variously regarded them as “non-uoccolithophore binary flsslon'as a basic similarity. The so far nanno1lths“(Haq, 1978) or dinoflagellate resting unique feature of Thoracosphaera is that the cysts (Fiitterer, 1976). Tangsn et al. (1982) dominant planktonic stage (the vegetative stage) showed that Thoracosphaera is a dinoflagellate consists of a non-motile cell completely enclosed with a life cycle unlike any other known for the in a calcareous sphere (stage I, Fig. 2). This group. contrasts sharply with the equivalent stage In The life cycle is not yet completely known, but almost ali other dinoflagellates (l.e. a typica! Tangen et al. ( 1982) showed that it includes a biflagellated motile stage enclosed by a cellulosic biflagellated motile phase identical with dino wall (stage 1, Fig. I ). . flagellates, establishing the true Identity of Thoracosphaera es a dinophyte. The role of this RESULTS FROM DEEP SEA SEDIMENT TRAPS motile stage in the life history remains unknown, Samples, from large sediment traps placed at but of particular interest here is the asexual different depths in the deep sea, during the division phase illustrated In figure 2. PARFLUX project, provided a unique opportunity -69- to supplement previous nonquantitative inform much less attention than the organic-wallet cysts ation from the two extremes of near surface that are thought to dominate most regions studied. plankton tows and bottom sediments. For the first Prior to this work, evidence regarding the time, an attempt was made to document the relative amounts of calcareous cysts versus remains of cysts and other life cycle stages of organic-walled cysts was restricted to just a few dinoflagellates sedimenting out through the deep studies from neritic environments. These soa water column and to compare them with cysts suggested that calcareous cysts 8re relatively previously described from Recent deep-sea moro Important In tropical rather than temperate sediments (Dale, in the press). regions. Dale (1976) reported only one to two Production of dinoflagellate resting cysts and percent in a Norwegian fjord, whereas Wall & thoracosphaerids (calcareous spheres referable to Dale ( 1968) found abundant calcareous cysts In the genus Thoracosphaera) is of main Interest tropical sediments, though never dominating the here. Station data and sample data are shown in assemblage to the extent seen in the deep see. At Table I. Three categories of remains of leest six types of calcareous cysts were recorded dinoflagellate life history stages: calcareous cysts, from the sediment traps, but by far the most organic cysts (i.e. non mineralized resting cysts), common type (accounting for over 905B) Is only and thoracosphaerids were counted ( Table 11 ). known from tile deep sea. Abundances and Sediment trap samples yielded many cysts, distribution of these cysts strongly suggest they supporting earlier observations by Wall et al. are regularly produced by oceanic dinoflagellates. (1977) that cyst formation is not restricted to Very few organic-walled cysts were seen in neritic dinoflagellates but includes oceanic types. sediment trap samples. Only one example was seen The most striking feature of the recorded cysts of the oceanic cysts cited by Wall et al. (1977). W8s the overwhelming dominance of calcareous This was surprising since elsewhere they are forms. commonly recorded from deep soa sediments and Calcareous cysts are unknown from freshwater, occasionally from slope water plankton. This mo/ and in neritic environments they have attracted be explained if relatively few organic cysts are Table I Summary of station dete and samples used for deep see dinoflegellate studies STATION PARFLUX PARFLUX E PARFLUX P, PARFLUX PB LOCATION 31*32.511 13*30.271 15*21.m 3*2111 55*35.41/ 54*00.11/ 151*28.511/ 81*53V OCEAN/BASIN Sohni abyssal Dealer ara E.Hawaii Panama plain abyssal plain abyssal plain basin TERM 10/76-1/77 11/77-2/78 7/78-11/78 8/79-12/79 DURATION 75 days HOdeys 98 days 112 days TRAP DEPTH («) (372) * 389 378 * 667 *(976) * 988 978 1,268 *3,694 *3,755 «2,778 (2,265) 5,206 *5,068 *4,280 *2,869 *5,369 *5,582 *3,769 *3,791 OCEAN DEPTH (m) 5,581 5,288 5,792 3,856 OEDII1ENÏ *Box core "Samples used for dinoflagellate studies. Trap samples represented size fraction <63pm (<250pm in -70- Table II Dinoflagellate cyst and thcracosphaerid fluxes per m2/dsy for trap samples documented in Table I. Stat. Trap-depth Dinoflagellate cysts: Thoraco- or genie calcareous sphoerlds S 1000m 6002 * 4000m 0704 » 5350m 2560 * E 389m 14 5537 * 988m 48 5809 • 3755m 48 13169 * 5068m 38 14546 • P 3000m 1968 1939! 4500m 1567 14125 5500m 401 2352 PB 667m 30 2392 30797 1268m 152 2438 29399 2869m 335 2591 33818 3769m 290 3626 35824 3791m 330 2337 24049 * not counted produced, on a scale not covered by this type of division) rathsr than resting cysts ( produced less sampling. Organic-walled cysts were seen in only frequently by sexual division). two stations, represented almost entirely by unidentifiable spherical brown protoperdinioid cysts. Protoperidinium species are probably BIOMINERALIZATION AND SINKING STRATEGIES heterotrophlc which correlates with the fact that the two stations mentioned ere significantly Studies of sediment trap samples end Thoraco nearer to continental land masses than are the sphaera in culture both suggest the somewhat other stations. These protopertdlniold cysts msy surprising conclusion that routine production of be reflecting hitherto unrecognized concentrations non-motile stages is an Important feature in the of heterotrophs below the euplwtic zone in such life cycles of several oceanic dinoflagellates. regions. Observations from material In culture show the Most of the thcracosphaerid) recorded (Table non-motile phases of Thoracosphaera to be II) were small calcareous spheres of T.heimii normal vegetative cells. The cysts recorded from or T. gran if oro. At stations P and PB (Table I) the deep sea sediment trops have never been they were roughly ten times more abundant than studied in culture. However, they era morphol dinoflagellate cysts. Though thoracosphaerids ogically similar to other dinoflagellate resting were not counted for stations S and E, many were cysts. They are presumed to serve tia seme basic observed Incidentally and they are presumed to be function of hypno2ygrtes in asexual cycle, though similarly abundant at those stations. Distribution obviously not es benthic resting stages at abyssa) of thoracosphaerids in trap samples suggests a depths. Alternative suggestions for their mode of steady flux of these through the water column. functioning are: I) their buoyancy may allow Their much greater rete of production compared them to remain suitably placed in the water io dinoflagellate cysts Is consistant with observ column (significantly, only empty cysts were see ations by Tangen at al. ( 1982) that they are sedimenting deeper In trap samples), or 2) they vegetative stages (produced more often by esoxual may complete their sexual function at a rate allowing excystment before the cyst sinks to a diatoms remains unknown, if massive bio depth from which the emerging motile stage con no mineralization in thoracospheerlds and calcareous longer reestablish contact with shallower cysts does represent a parallel sinking strategy to plankton (Dale, in the press). that of the diatoms, other dinoflagellates with a Another surprising feature of oceanic life cycles combination of mineralized skeletons and flagella was the heavy mineralization of non-motile may be similarly paralleling the combined stages. Blomlnerallzatlon is known in only a few sinking/swimming strategies of e.g. cocco other dinoflagellates, mostly restricted to a few lithophorids. forms with siliceous internal skeletons, (e.g. Smetacek (1985) aiso suggested other sinking Tappan, 1900: 250-256) and some other mechanisms for diatoms that may have analogies calcareous cysts (e.g. Wall & Dale, 1968). Thick with some other types of cysts known from neritic calcareous walls suggest a possibility for a dinoflagellates. He noted "increased mucous sinking strategy, least expected in oceanic secretion in conjunction with the cell pro dinoflagellates. Nevertheless, particularly since tuberances characteristic of bloom diatoms leads heavily mineralized non-motile stages figure in to entanglement and aggregate formation during two different life history stages (vegetative and sinking; the "sticky" aggregates scavenge sexual) of two different groups of dinoflagellates, minerals and other particles during decent which this may well represent a common sinking further accelerates the sinking rate”. Many cysts strategy coupled to biomineralization. Such posses a variety of spines that certainly lead to strategies are found in other planktonic groups. entanglement (both with other cysts end debris) The major phytoplankton groups, diatoms, and aggregates, while several cysts are known that dinoflagellates, and coccoiithophorids are geo are coated with a mucous layer which scavenges logically old, extending back through the Mesozoic minerals and other particles (e.g. Dale, 1977). Era. They have maintained their separate Such mechanisms may aiso serve to help benthic identities while presumably sharing the same resting cysts in maintaining their position in environments because of basic, strong, equally bottom sediments during the resting period, viable differences within their total biologies; resisting possible washing out by bottom almost certainly including factors such es currents. biomineralization and life cycle strategies. The advantages of the sinking strategy fo»' Considered from this point of view the groups mery oceanic dinoflagellates are not known but be cliaracterfzed thus: diatoms utilize bio presumably they are similar to those forming Ute mineralization os the basis for a non-rnotile basis for diatom strategies, lhese may include sinking strategy, dinoflagellates generally do not removing tile cell from nutrient poor weters of utilize biomineralization but employ flagella iii a the euphotlc zone at times of particular depletion swimming strategy, and coccolithophorids to nutritionally richer waters usually found a possibly utilize a combination of the two with both little deeper in the water column, and advantages mineralization and motility combined, though the of long distance lateral transport (assuming a sinking strategy may predominate. degree of buoyancy) to other regions of improved Smetacek ( 1985) summarized those features of nutrients (e.g. upwelling). diatoms that may be interpreted as constituting the basis for a sinking strategy, thus offering comparisons with the oceanic dinoflagellates. Of REFERENCES particular interest is the obvious value of the -ANDERSON, D. M.. A. WHITE & D. BAÜEN (eds), heavily mineralized frustum as balast for helping 1986. Toxic dinoflagellates. Elsevier, N.Y. the diatom to sink. The heavily mineralized shells -DALE, B., 1976. Cyst formation, sedimentation, and of thoracosphaerids and calcareous dinoflagellate preservation: factors affecting dinoflagellate as cysts are here considered probably to serve a semblages in Recent sediments from Trondheimsfjord, similar function, though the extent to which these Norway. Rev. Palaeobot. Paly no!., 22 \ 39-60. cells can regulate their own buoyancy 83 do -DALE, B., 1977. Cysts of the toxic red-tide -72- dinoflagellate Gonyaulax excavata (Braarud) Balech from Oslofjorden, Norway. Sarsia, 63: 29-34. -DALE, B., 1903. Dinoflagellate resting cysts: ’benthic plankton’. In: 0. A. Fryxell (ed.) Survival strategies of the Algae. Cambridge Univ. Pross : 69-136. -DALE, B., (In the pross). Dinoflagellate contributions Io the open ocean sediment flux, in: S. Honjo (ed.) Biocoenosis in the open soa. Mlcropaleontol. Press -DALE, B., (in the press). Thoracosphasrlds In the open ocean sediment flux. In: S. Honjo (ed.) Biocoenosis in the open soa. Mlcropaleontol. Press -DALE, D. fit C. S. YENTSCH. 1976. Red tide ar.d paralytic shellfish poisoning. Oceanus, 2! (3): 41-49. -FÜTTERER, D.. 1976. Kalkige Dinoflagellaten ("Calciodinelloideae') und die systematische Stellung der Thoracosphaeroideae. N. Jb. Geo!. Paleontol. Abh., 151: 119-141. -HAQ, B. U., 1978. Calcareous nannoplankton. in: B. U. Haq 6. A. Boersma (eds) Introduction Io marine micropaleontology. Elsevier-North Holland, New York: 79-107. -SMETACEK. V. S., 1985. Role of sinking in diatom life-history cycles: ecological, evolutionary and geological significance. Mar. Biol., 84: 239-251. -TAN6EN, K.. L. E. BRANO, P. L. BLACKWELDER & R. R. L. SUILLA!», 1982. Tltor Otosphaera heimii (Lohmani Kamptner Is a dinophyte: observations on lis morphology and life cycle. Mar. Micro- pa loon tol., 7: 193-212. -TAPPAN, H.. 1980. The paleobiology of plant protists. Freeman, San Francisco: 1028pp. -WALL, D. & B. DALE, 1968. Qjalernary calcareous dinoflagellates (Calclodinellideae) and their natural affinities. J. Paleontol., 42 : 1395-1408. -WALL. D., B. DALE, G. P. LCHMANN fit W. K. SMITH, 1977. The environ.Ti»nlal and climatic distribution of dinoflagellate cysts in modern marine sediments from regions in the North and South Atlantic Oceans and adjacent seas. Mar. Mlcropaleontol. 2 : 121-200. -WALKER, L. M.. 1985. Lire histories, dispersal, and survival in marine, planktonic dinoflagellates. In: K. A. Steidinger fit L. M. Walker (eds) Marine plankton Ufa eyela strategies. CRC Press, Boca Raton : 20-34. -73- THE AZORES FRONT: A Z006E0GRAPHIC BOUNDARY ? P.A.DOMANSKI Institute of Oceanographic Sciences, U.K. INTRODUCTION 50-608 of the chlorophyll levels of the EAW. However, despite the potential for greeter mixing The zoogeography of the mesopelagic fauna of the in the front there was no evidence of consistently N.E.Atlantic is reasonably well understood only higher phytoplankton productivity levels In the for a handful of taxonomic groups (Ostracoda: frontal region. During May and June 1981 the Angel & Fasham, 1975; Fasham & Angel, 1975; front propagated westwards by some 55km, at the Fish: Backus et al., 1977; Decapod crustaceans: same time a tOOkm diameter EAW eddy was Foxtcn 1972; Casanova, 1977; Fasham & Foxton, pinched off from a meander and moved westward at 1979). Fasham & Foxton ( 1979) showed that the 2.2km d'1. zonation of decapods sampled at IO' intervals from 10'N to 60'N along the 20'W meridian, could largely be explained In terms of the ocean's NET SAMPLING hydrography. Their > 1000km spacing yielded faunal regions with apparently clear boundaries Five stations were occupied: in the WAW, in a between them but on this scale the precise nature WAW meander, in the front, in the EAW and in the of the transition areas could not be determined. In newly formed EAW eddy. At each station a day ond a this paper the boundary between two water night series of hour long net hauls were fished masses is examined in greater detail with respect over 100m depth horizons to at leest 1200m to the decapod crustacean faunal assemblages. depth using an opening/closing multiple RMT 1 +8 The area under consideration here Is a region to system ( Roe & Shale, 1979). the S.W. of the Azores on the eastern flanks of the Mid Atlantic Ridge (Fig. 1). Through this arra runs an extension of the southerly return branch RESULTS of the Gulf Stream ond this gives rise to a permanent oceanic frontal region, referred to es A total of 56 species of decapods were identified the Azores Front (Qould, 1985). from 126 hauls. Of these 34 spp. were cosmopol itan, seven occurred only at one station and, of the remainder, only two or three species showed any PHYSICAL BACKGROUND semblance of an FAW-WAW dina In terms of presence/absence. The abundance of the 15 During 1980/81 the Institute of Oceanographic dominant species from each station ara given in Sciences mounted a programme to investigate the Table I. Clearly the major ity of abundant species Azores Front. It v/gs found to be a meandering were most numerous in the Front and scarcest in feature 20-50km wide, characterized by rapidly tho WAW. This pattern is repeated in biomass es changing isotherm depths across it and high noar indicated by the displacement volume of animals surface currents of 440cm s"1 along It. On one contained under 10m2 of ocean surface from aide of the front lay' Eastern Atlantic Water 0-1200m depth range averaged over day and (EAW) typified by the 16'C isotherm depth of < night: WAW (4.2cm3), EAW (6.5cm3), 150m, on the other side lay Western Atlantic W.Meender (7.7cm3), E.Eddy( 8.3cm3) and Front Water (WAW) with the 16'C isotherm >300m. (9.4cm3). Fasham et al. ( 1985) reported that the WAW was Kendalls Rank Correlation was used to derive generally poorer In nutrients and had only dendrograms of similarity between stations using -74- 1 Western Atlantic Wafer 2 Western Meander 3 Front 4 Eastern Atlantic Water 5 Eastern Eddy 4 5 3 2 1 Salinity %o Fig. 1 a. The stud/ ares to the S.W. of the Azores, b. The position of the front during late Spring 1981 es defined by Ute location of 16'G Isotherm at 200m. c. T/8 curves for the five stations, a displacement of 0.1 0/00 is used to separate them. For station details refer to the Appendix. -75- Table I is compiled using the 15 most abundant species from each station. Values given are numbers of animals under 10m2 of sea surface. Bathypelagic species whose population ranges have not been fully sampled are denoted by an asterisk. Species WAW W.Meander Front EAW E.Eddy 10380 10378 10376 10379 10382 Oeridee: Acanthephyra purpurea 1.37 5.68 4.77 3.17 5.21 Acanthephyra pelagica 0. 0.19 0.61 0.69 0.03* Acanthephyra stylorostratis 0.65* 0.15* 0.56 0.26* 0.12* Systellaspis debilis 1.23 1.63 1.27 1.09 1.46 Oplophorus spinosus 0.36 0.51 0.65 0.66 0.70 Parapandalus richardi 0.48 0.71 0.54 1.0 0.45 Parapasiphaea sulcatifrons 0.14 0.35 0.77 0.67 0.42 Hymenodora gracilis 1.12* 0.71* 3.19* 4.69* 0.40* Hymenodora glacialis 0.28* • * 0.08* « Sergestidae: Sergestes (Sergia)robustus 0. 0.06 1.77 0.05 0.24 Sergestes splendens 0.45 1.07 0.68 1.04 1.20 Sergestes japonicus 0.25 1.70 6.50 1.79 1.11 Sergestes tenuiremis 0.13 0.52 0.28 0.16 0.72 Sergestes ( Sergestes J vigilax 0.30 0.33 0.98 1.57 1.01 Sergestes sargassi 0.12 1.27 1.89 1.35 0.62 Sergestes henseni 0.12 0.17 0.56 0.05 0.06 Sergestes curvatus 0.13 0.61 0.25 0.79 0.55 Sergestes atlanticus 0.06 0.12 1.95 1.31 0.83 Petalidium obesum 0.42* 0.10* 0.37* 0.16* 0.13* Penaeidae: Oennados elegans 0.01 0.23 3.76 1.91 0.96 0. valens 0.39 4.51 2.58 1.95 2.26 Bentheogennema intermedia 0.99 6.58* 3.18 5.18 4.05* Funchalia villosa 0.32 0.24 0.05 0.26 0.18 Luciferidae: L ucifer sp.( larval stages) 2.90 0.25 0.08 0.28 0.14 the standardised totals of the 20 most abundant of species typifying the main patterns of species (Fig. 2). For both adult and non-adult abundance across the front. Among the three animals the WAW stands apart from the others and major decapod taxa the robust diet migratory the EAW and E.Eddy are linked together in both carida exhibited the least diminution toward the cases. Although greatest overall similarity occurs WAW. Acanthephyra purpurea, Op Iop bo between Frontal and W.Meander adult faunas this reus spinosus, Parapandalus richardi relationship is of less significance for non-adult and Systellaspis debilis, whose vertical stages. ranges are largely confined to the top 1000m of Figure 3 shows the distributions of a selection the water columba!! deepen slightly toward WAW -76- In a trend common to the >9*C isotherms, this is species Bentheogennema intermedia was aiso most pronounced in the nighttime distributions scarcest in the WAW but most abundant in the which are shallower. Certain bathypelagic carida W.Meender. aiso change across the front, A. pelagica, which Apart from several of the larger Sergia spp. at these latitudes displays only slight diel the sergestids aiso were scarce in WAW. Two migration, 3hoals and becomes more numerous species, Sergia robustus and S. japonicus, toward the EAW. Conversely, the non-migratory a migrator and non-migrator respectively were A. stylorostratis shoals and becomes numerous markedly more abundant in the Front than in the WAW, these latter two species appear to be elsewhere. mutually exclusive. Ali three Acanthephyra species are abundant in the front although they are segregated by depth. DISCUSSION Unlike the study by Griffiths and Brandt (1983) in the East Australian Current, an During the past two decades it has become analysis of length/frequency of carapace length increasingly clear that the traditional view of for the most common carida revealed no stable and homogeneous oceans can be quite significant differences in size structure between erroneous. Mesoscale features on a scale of 10s to the five stations. Likewise the size and ratios of I OOs of km and months to years in duration have gravid to non-gravid females indicate that the been reported In ali the oceans, and the N.E. same populations were sampled at each of the five Atlantic is no exception (e.g. Madelain & Kerut, stations. 1978; Oould, 1985). Horizontally, faunal Gennadas elegans a deep mesopelagic species transitions may be broad averaging out the effects and exhibiting no diel migratory habit at these of any mesoscale activity or narrow but exhibit latitudes was the most drastically affected of the variability on similar scale to the hydrography. Gennadas group by the transition from EAW to In studies of both the Gulf Stream Rings (e.g. WAW. Poorly represented in the W.Meender, it Wiebe et al., 1976) and the East Australia WBs virtually absent in the WAW proper. Current (e.g. Griffiths & Brandt, 1983) 0. valens, however, displayed extensive vertical biological variability has been observed on a migrations, was scarce in the WAW, but very similar scale to that of the hydrography. abundant in the W.Meender. The bathypelagic Mesoscale variability has aiso been strongly suspected when there have been unexpected faunal discontinuities during otherwise routine sampling ADULTS (Angel, 1977). The decapod assemblages considered here provide evidence for both slow and rapid response to such mesoscale activity. Depth(s) of habitation and vertical mobility may, to an extent, determine geographical distribution es differences in the current sheer with depth can affect patterns of dispersal (Miller, 1970). The vertically migrating carida are physiologically adapted to cope with a wide T/S range so, to these animals, the front represents no major obstacle. Faunal change for them, if any, across the front is only gradual. Vertical migration, however, is modified as there is a slight downward trend in the upper depth Fig. 2 Similarity relationships between the limit following the pattern in Isotherms; this has faunas of the five stations derived from Kendalls been noted elsewhere (e.g. Acanthephyra spp. Rank correlation. Foxton, 1972 and more generally; Chaetognatha, IOOY EOOY EOOY filtered. E E E 10362 10362 10362 water of 500- 3 m 4 10 £AV nos. 10370 are - bars 1000 1500- Night. Histogram FRONT histograms: 10376 -77- front. I - — the shaded 500- 1000 1500- 2000 Da/, across >#CR WOR WCR V V « species histograms: 10376 10378 10378 - 500 selected pelagica purpurea stylorostratis of Unshaded 4 -• » 2 VAV VAV VAV f meters. - L 2 in 10390 10360 10360 Distribution --- 1 is 4 Acanthephyra Acanthephyra Acanthephyra 3 o 0 0 500 500 ?ooo 1000 1500 1000 1500 2000 1500 500 1000 2000 *«*•0 M»Ö*Q md*a Fig. Depth Fig. 0*plh D*pth 3 Gennadas Bentheogennema Qennadae 30 40 continued 10300 10300 15 20 VAV VAV 15 20 valent «lagena 30 40 Intermedia 30 40 10370 10370 15 20 V V WGR MGR 15 20 30 40 30 -78- 10370 10370 IS FRONT FRONT 15 20 30 40 30 40 10379 IS 20 EAV 15 20 30 40 30 40 10302 10302 15 20 E E EOOY EOOY 15 20 30 40 Fig. Depth c*frth 0«pth 2000 1000 3 -* - Sergestes Sergestes 12 continued 10360 10380 0 Sergia 10370 10CJ WAV japonicus VAV ?0 IO 0 20 vigilax 40 atlanticus 12 1500 1500- 500 10370 - - - 20 40 12 10378 10370 ?o IO 0 V 9 V NMDR WOR ?o IO 0 20 12 2000 1000 2000 1000 1500 1000 500- 500 - '1 - - 40 10370 10370 79 20 FRONT FRONT FRONT 20 IO 20 2000 1500- 1000 1000 1500- -I - - 20 40 12 10370 10370 ?0 IO 0 EAV EAV IO 0 c-0 12 1000 2000 1500 1000 -J - - 20 40 12 I03f>: io»? 10362 20 i0 0 E c £ EOOY tooi £007 IO 0 20 12 -*0- Systellaspls debilis 10390 WAW 10370 V WOR 10376 FRONT 10378 EAW 1038? E EOOY eo io io eo ?0 IO IO ?0 IO IO eo io IO eo ?0 IO IO 500-J 50ü- 500- soo ~ 1000 - 1000 - 1500 - 1500- 1500 - eooo -J eooo-1 Parapandalus richardi 10390 WAW 10378 W UNOR 1038? E EOOY Sergia grandis 10380 WAW 10378 W KH)R 10376 FRONT 10379 EAW 1038e E EOOY 500- 500- 500- 1000- 1000- 1500- 1500- eooo Fig. 3 continued -Bi- Pierrot-Buits, 1975; euphausiids, Wiebe & possibly by the enhanced primary productivity In Fileri, 1983). As non-selective carnivores, the edge region (Tranter et al., 1983). This (other then for size of prey; Foxton & Roe, 1974; higher productivity, they argued, could be Roe, 1985) the vertically migrating caridsmay transmitted through to higher trophic levels be particularly trophically adaptable across the (Boyd et al., 1978). In this study no such front. enrichment wss found in the region of the front There are examples In which the migratory and (Fesham et al., 1985), however, it is unlikely non-migratory habits are exhibited by species that the increased micronekton resulted from a which are congeneric and it is the deeper, past phytoplankton enrichment in the immediate non-migratory species that are most restricted in vicinity es advection in the relatively swift distribution across the front. Acanthephyra frontal currents would tend to be dispersive. The pelagica only a partial migrator and A. time taken for decapods, which are close to the top stylorostratis a non-migrator, are more of the food chain, to respond to an increase in abundant in the EAW and WAW respectively, both phytoplankton will be considerable. Assuming reside mainly below 800m. A. purpurea, entrainment in the front and an average current of however, which undergoes extensive vertical I Ocrns”1, >500 km could be covered in 2 months, migrations is more evenly distributed between the nearly the same length of time tsken to sample the five stations; note that In the front ali three five stations. The general trend of the front is NW species thrive but are vertically segregated. to SE (Mann, 1967; Oould, 1985), it is very Amongst the Gennadas type species, G. valens likely, therefore, that species of high abundance occurs in ali five stations (although scarce in in the front (e.g. Sergia japonicus and S. WAW) and performs vertical migrations similar robustus were advected from more productive to those of A.purpurea 0.elegans, however, areas to N.W. which dwells below 800m and does not migrate in Attempts to identify zoogeographical regions and this area, is scarce in tho W.Meander and absent to relate them to water masses have met with from WAW. It Is noticeable that faunal differences varying degrees of success and it is now clear across the front are most evident below 800m that, whilst the distribution of many species can despite only very small differences in T/S broadly be explained in these terms, the limits of relationships at this depth. species ranges rarely coincide exactly with One could speculate that the scarcity of physical boundaries. This present study is in Gennadas in the WAW may be In part due to agreement with this view as, the Azores Front their high degree of detritivory (Foxton & Roe, which is a marked physical feature between 1974; Heffernan & Hopkins, 1981; Roe, 1985). distinct water masses, represents the boundary Detritus, high in faecal material may be of only a few species. In terms of presence/ particularly lacking in WAW because of the absence, therefore, there is little to distinguish generally lower productivity of these waters. The the five decapod assemblages. However, a pattern scarcity of sergestids, particularly small does emerge from the comparison of ranked Sergestes spp. in WAW and W. Meander is not abundances which shows that the EAW and EAW easily accounted for. Most species are diel vertical eddy stations ere closely linked while the WAW migrators and thus able to cope with a consider one stands apart. able T/S range. Out analyses are few but indicate a The existence of structured pelagic communities diet of small micronekton and plankton with a that are distinct from one another has been degree of detritivory (Roe, 1985). questioned more than once (e.g. for Diatoms: The greater abundance in the front and the two Williams et al., 1981; and Fish: McKelvie, other stations between EAW and WAW is difficult 1985). Differences in the environment on either to account for on available evidence alone. side of the front will, not unnaturally, favour Griffiths & Brandt (1983) reported greater some species more than others and thus lead to numbers of some decapod species and higher C:N differences in relative abundance, the significance ratios in the edge region of an edd/, caused of which are difficult to interpret. The study area -02- is subject to quite pronounced mesoscale varia -CASANOVA, J. P., 1977. La fauna pélagique bility which is in addition Io any seasonal profonda (zoop/encton et necton) de la influences and so it is likely that in the region of Province atlanto-mêditarranéenna. Aspects the front, at least, the relative abundances are in taxonomique, biologique et zoogéographique. a state of constant flux. Thèse Doei. Etat-Sci. Nat. Univ. Aix-Marseille: 1-455. The role of trophic relationships me/ well be -fASHAM, M. J. R. & M. V. ANGEL. 1975. The very important (e.g. Pugh, this volume) although, relationship of the zoogeographic distributions of Ute as yet, they are only poorly understood for this planktonic oslracods in the North-east Atlantic Io the region. In their study of thermal fronts Backus et water masses. J. mar. bid. Ass. U.K., 55: al. (1969) postulated that some species of meso- 739-757. pelagic fish were particularly well adapted to -fASHAM, M. J. R. 8, P. FOXTON. 1979. Zonal arces of either high or low productivity, perhaps distribution of pelagic Decapoda (Crustacae) in the the same is true for other taxa. In the WAW, the eastern North Atlantic and its relation to the physical lowest biomass was recorded in most other oceonography. J. exp. mar. Biol. Eco!., 37 : micronektonic and planktonic taxa as well as the 225-253. decapods, this was most probably due to the low -FASHAM. M. J. R.. T. PLATT, B. IRWIN 8, K. JONES. levels of primary productivity. The decapod fauna 1985. Factors affecting the spatial pattern of the deep is especially lacking in detritivorous species. By chlorophyll maxima in the region of the Azores Front. this measure the WAW could be said to have a low Prog. Oceanogr., 14: 129-166. -fOXTON, P.. 1972. Observations on the vertical productivity fauna, the fact still remains, how distribution of the genus Acanthephyra (Crustacae: ever, that the species complement is substantially Decapoda) in the eastern North Atlantic, with the same es the other four series, distinguished by particular reference Io the 'purpurea' group. Proc. the lack of some species rather than the addition of R. Soc. Edinb., B. 73: 301-313. others. -fOXTON. P. & H. S. J. ROE. 1974. Observations on the nocturnal feeding of some mesopelegic decapod Crustacea. Mar. Bid., 26: 37-49. REFERENCES -GOULD, W. J., 1985. Physical oceanography of the Azores Front. Prog. Oceanogr., 14: 167-190. -ANGEL, n. V.. 1977. Studies on Atlantic halocyprid -GRIFFITHS. F. B. 8» S. B. BRANDT, 1983. Distribution oslracods: vertical distributions of the species in the of mesopelaglc decapod Crustacae In and around a Iop 1000m in the vicinity of 44'N 13*W. J. mar. warm-core eddy in the Tasman Sea. Mar. Ecol. bid. Ass. U.K.. 57: 239-252. Prog. Ser., 12: 175-184. -ANGEL, M. V. & M. J. R. FASHAM, 1975. Analysis or -HEFFERNAN, J. J. 8. T. L. HOPKINS, 1981. Vertical the vertical and geographic distribution of the distribution and feeding of the schrfmp genera abundant species of planktonic oslracods in the Gennadas and Bentheogennema (Decapoda: Penaeidea) North-east Atlantic. J. mar. biof. Ass. U.K. 55 : in the eastern Gulf Stream of Mexico. J. Crust. 707-737. Bio!., I: 461-473. -BACKUS. R. H., J. E. CRADDOCK, R. L. HAEDRICH 8, -MANN, C. R., 1967. The termination of the Gulf 0. L. SHORES, 1969. Mesopelaglc fishes and thermal Stream and the beginning of the North Atlantic fronts in the western Sargasso Sea. Mar. Bid., J: Current. Deep-Sea Res., 14 : 337-360. 87-106. -MAOELAIN, F. & E. KERUT. 1978. Evidence of -BACKUS. R. H.. J. E. CRADDOCK. R. L. HAEDRICH 8. mesoscale eddies in the Northeast Atlantic from a B. H. ROBISON, 1977. Atlantic mesopelaglc zoogeo drifting buoy experiment. Ocaanol. Acia, 1 : graphy. In: R. H. Gibbs (ed.) fishes or the western 159-168. North Atlantic. Mem. Sears Fdn mar. Res. / -McKELVIE, D. S., 1985. Discreteness of pelagic (7 ): 266-287 faunal regions. Mar. Bid., 68: 125-133. -BOYD, S. H„ P. H. WIEBE & J. L. COX. 1978. Limits -MILLER, C. B., 1970. Some environmental of Nematoscelis megalops in the northwestern consequences of vertica) migration in marine Atlantic in relation Io the Gulf Stream cold-core zooplankton, limnol. Oceanog.. 15: 727-741. rings. Part II. Physiological and biochemical effects of -PIERROT-BULTS, A. C.. 1975. Taxonomy and expatriation. J. mar. Res.. 56: 143-159. zoogeography of Sagitta planctonis Steihhaus 1896 -03- (Chaetognatha) in the Atlantic Ocean. Beaufortia, 23: 27-51. -ROE, H. S. J., 1905. The (Hoi migrations and distributions within a mesopelagic community in the Northeast Atlantic: 2. Vertical migrations and feeding in mysids and decapod Crustacea. Prog. Oceanogr., /J: 269-31 B. -ROE. H. S. J. 8* 0. M. SHALE. 1979. A new multiple rectangular midwater trawl (RMT 1+8M) and some modifications Io the Institute of Oceanographic Sciences’ RMT 1+8. Mar. Bioi., 50 : 283-288. -TRANTER, 0. J., 6. S. LEACH 8» D. AIREY, 1983. Edge enrichment in an ocean eddy. Aust. J. mar. freshw. Pes. 134: 665-689. -WIEBE, P.H., E.M. HULBERT. E. J. CARPENTER, A.E. JAHN. G. P. KNAPP. S. B. BOYD. P. B. ORTNER & J. L. COX, 1976. 6u)f Stream cold core rings: large scale interaction sites Tor open-ocean plankton communities. Deep-Sea Pes., 23: 695-710. -WIEBE, P. H. & G. R. FLIERL. 1983. Euphausia fnvasion/disperal In Gulf Stream cold-core rings. Aust. J. mar. freshw. Pes., 34: 625-652. -WILLIAMS. W. T., J. S. BUNT, R. D. JOHN 6, D. J. ABEL, 1981. The community concept and the phytoplankton. Mar. Eco/. Prog. Ser., 6 : 115-121. APPENDIX Station Position of centre Dates 1981 Depth of the 16*C Isotherm (inm) 10376 Frontal 33*20'N 33‘20'W 26/5-30/5 295 10378 WAW Meander 32‘20'N 29‘50'W 7/6-10/6 254 10379 EAW 35‘00’N 33‘10’W 11/6-15/6 146 10380WAW 30‘00'N 33'50'W 16/6-20/6 318 10382 EAW Eddy 32‘33‘N 32‘33'W 21/6-24/6 194 Abbreviations: EAW (Eastern Atlantic Water) WAW ( Western Atlantic Water) -M- THE PLEISTOCENE EQUATORIAL BARRIER BETWEEN THE INDIAN AND PACIFIC OCEANS AND A LIKELY CAUSE FOR WALLACE S LINE ABRAHAM FLEMINGER Scripps Institution of Oceanography, U.S.A. INTRODUCTION the basis for a series of proposed biogeogrephical boundaries (Fig. 1) that extend north to south Between Miocene and Pliocene time 15 to 5 across eastern Indonesian seas between the east million years ago, the Australian/New Guinea coast of Borneo and the western end of Vogelkop plateend the Asian plate collided (Audley-Charles Peninsula off western-most New Guinea (Carr, et al., 1981; Audley-Charles, 1981) and 1972; Raven & Axelrod, 1972; George, 1981). established the contemporary alignment of land The extreme boundaries are Wallace's line lying and sea in the Indo-Australian region. Subsequent east of the Philippines and passing south between eastward dispersal of some oriental terrestrial Borneo and Celebes and Lydekker's line, a dogleg plants and animals and westward dispersal of some lying west of New Guinea and east of Ceram and the Australian / New Guinean terrestrial species Kai and Tanimbar Islands. The two lines delineate across1 the collision boundary apparently failed. an area of biotic transition between Asian and The imperfect dispersal of the two biotas became Australian/New Guinean faunas and floras some- Huxley's Une 1868 » *£> Wallace's Une 1863 - 1880 ..■Wallace's Une 1910 , MALAYA Weber's Une 1904 ..^Lydekker's Une 1896 BORNEO VOGELKOP NEW ./ # /|aru GUINEA 'k /tanimbar Weber's Une 1894 Sahul shell Fig. 1 Biogeographic boundaries proposed for separating the Oriental and the Australia/ New Guinea faunal regions, (cf. George, 1981 ). -05- times referred to os Wallacea (Mayr, 1944). proportion of high biomass stations were the Wallacea encompasses the eastern Indo- nesian highest of the cruise, and almost ali the samples se8s, the major tropical seaway connecting the contained upwelling species. Furthermore, the Indian and Pacific Oceans and the only tropical sector C samples contained few if any of the 40 connection during Pleistocene glacial stages. stenothermal species of Pontellidae that were In this paper I consider several lines of collected In the course of the expedition. High evidence that Wallacea was the likely site of values in sector D appear to be the consequence of profound, vlcarient events during Pleistocene advection from sector C. Sector A aiso had low glacial stages. These events influenced the temperatures, few pontelllds, end sufficient distribution and spéciation of pelagic, equatorial, phytoplankton to discolor the net, but, in view of Indo-Paclflc stenothermal species Inhabiting the the low zooplankton biomass and the scarcity of mixed layer. Support for the hypothesis that upwelling copepods, the upwelling was clearly in Wallacea hss been a geographical barrier during an earlier phase of development. The cause of the Pleistocene glacial stages derives from several upwelling appeared to be the SE Trade Winds sources: blowing 15 to 25 knots, day and night, during this 1. Evidence of annual coastal wind driven up- phase of the southern hemisphere winter. welling off western New Guinea. A series of histograms (Fig. 3) allows one to 2. Presence of an upwelling species endemic to the compare surface temperatures with ( 1 ) biomass, Indo-Austral Ian region, Calanoides philip (2) the occurrence of the upwelling copepods, pinensis. Calanoides philippinensis and Rhincalanus 3. Estimates of reduced surface water temper nasutus and (3) the abundance of stenothermal atures in Pleistocene glacial periods. copepods belonging to the family Pontellide. 4. Spéciation patterns of pontellid copepods in Station numbers are shown at the bottom of the habiting surface waters of the Indo-Australian figure. Samples were taken with a I m plankton region. net fished horizontally at the surface for twenty 5. Presence of an apparent hybrid zone across minutes at dawn or dusk. Stations 40 to 60 located Wallacea in copepods of the genus Undinula. south and west of New Guinea produced the lowest temperatures, the highest biomass, the largest numbers of upwelling species, and the lowest UPWELLING OFF NEW GUINEA abundance of stenothermal pontelllds. Typical surface temperatures at coastal water stations, Upwelling in Wallacea first came to my attention sampled at dawn and jjusk, measured 28*C. At in midyear of 1979, in the course of a biological midday they tended to rise to 30*C. Minimum see collecting expedition aboard R/V Alpha Helix surface temperatures of 25*C were apparently working coastal waters in eastern Indonesian sess. depressed about 34C by the upwelling. Figure 2 shows the track of the expedition. Although phytoplankton biomass was not To facilitate comparisons, the track has been measured, it should be noted that stations divided arbitrarily into sectors labeled A, B, C, D producing high zooplankton biomass and low & E. Median surface temperatures and mean surface temperatures ( <27'C) tended to have high zooplankton biomass, sector by sector, are shown quantities of phytoplankton contributing to the in the table 8bove the cruise track (Fig. 2). green, turbid qualities of the water observed at Circled stations had zooplankton biomass, these localities. Furthermore, at these stations measured as displacement volume, above 150cc and many stations of sector A the zooplankton net per standard tow; half-filled and filled circles are usually came aboard coated with a thick green stations at which upwelling species of copepods layer of phytoplankton. The highest concentrations were collected. of upwelling species, highest zooplankton biomass Sector C showed the most pronounced effects of measurements, and the lowest temperatures coastal upwelling. Surface temperatures were as occurred Just west and north of the Aru low 8s 25'C, mean zooplankton biomsss and the Archipelago. -86- I2I*E 125* 130* 135* KO* 145* 150* 155* Surface Sector Biomass,cc Temp.,°C No. Obs. X (range) Median (range) A 78 (14-178) 26 (26-28) B 86 (11-200) 29 (28-30) 23 C 155 (42-441) 26 (25-30) 17 D 119 (51-220) 28 (27-29) 8 E 61 (7-155) 29 (28-30) 19 ar guinea Fig. 2 Cruise track, Moro Expedition 31 May to 24 July 1979, aboard RV "Alpha Helix", lm net, 505 mesh, towed at surface for 20 minutes at dawn or dusk at numbered stations. Biomass, measured and reported as displacement volume per 20-minute surface tow, exceeded 150cc at stations marked by a circle. Circles half filled and filled aiso indicate presence of one or two upwelling species of copepod, respectively. Sectors A to E, determined arbitrarily, provide means for highlighting area of low surface temperature, high biomass and frequent occurrence of upwelling copepods. COPEPOD UPWELLING SPECIES IN THE much more widespread in this region. Most Indo- IND0-AU5TRALIAN REGION Malayan records of R. nasutus and C. phi 1 ip - pinensis taken by the two previous expeditions Biogeographically, the two upwelling species are In Indonesian waters, Siboge (Scott, 1909) and very different. Rhincalanus nasutus appears Snellius (Vervoort, 1946), were aiso obtained to be circumglobal and occurs primarily in from west and south of New Guinea ( Fig. 4). I have temperate boundary currents and in tropical aiso found C.philippinensis in this region in upwelling. My unpublished data on Calanidae surface collections taken off southwest New Guinea which include a cladistic analysis of phylogeny and in midyear, 1976 and 1977, by an SIO expedition a blogeographtc study of Calanoides supports the called INDOPAC. Thus, there is ample reason to hypothesis that C.philippinensis evolved accept two facts with significant historical relatively recently within the Indo-Australian implications for Wallacea. I. Upwelling is an region and probably at a time when upwelling was annual midyear event In the southern hemisphere -87- Fig. 3 Moro Expedition, 31 Mar/to 24 July 1979. Histograms of temperature, biomass (eo) es displacement volume per 20-minute surface tow, abundance of upwelling species, Calanoides philippinensis and Rhincalanus nasutus, no. adults/m3 shown by tick to left of vertical line, no. juvenlles/m3 shown by tick to right of vertical line; lowermost histogram shows sum total of stenothermal species of copepod family Pontellidae represented in samples of expedition by 15 species of Pontella, 14 species of Labidocera and 11 species of Pontellopsis. 52 1795 Calanoides Station numbers shown on scale at bottom; 27 philippinensis stations 40 to 60 with lowest temperatures, highest biomass, largest numbers of upwelling species and lowest numbers of stenothermal pontelllds. Subsamples were obtained with the aid 0 L 107 1730 Rhincalanus of a Folsom plankton splitter for large, highly 2 r nasutus varied samples and a Stempel pipette for small samples dominated by copepods. Counts, usually 0 iii based upon microscopic examination of 5£ of the Pontellid stenotherms 47.21 total sample, the range varying from 2% to 10*. ■ 11 m 1111 il 11 h 111111111111111111111111 il 1111111111111 32 I 44 I 55 I 69 winter prompted by the winter-intensified SE copepodites), C.phi/ippinensis appears to Trade Winds. behave ss do its allopatrlc congeners. They tend to 2. Calanoides philippinensis appears to have enter the mixed layer during seasonal periods of evolved in the vicinity of Wallacea and probably enrichment where they mature and reproduce. during a period when the cool water conditions, Late Immature individuals (i.e. stage Y and the dense phytoplankton populations it Copepoda) of the next or some subsequent favours, were much more extensive than they are generation store large quantities of lipids. They now. Compared to the huge populations of its leave the mixed layer apparently when food congeners off Africa, South America, South supplies decline precipitously (Smith, 1982) to Australia and the Antarctic, C.philippinensis enter diapause at about 300 to 500m or deeper. appears to be barely surviving at present. The diapausing stocks remain as late juveniles at Extrapolating from available sampling records depth until the onset of the next upwelling period (Figs 3, 4)(deep tows from Siboga and Snellius es described for Calanoides carinatus and Expeditions produced only late copepodites, Calanus pacificus californicus (Binet & surface tows in winter months from Moro and Suisse de Saint Claire, 1975; Petit & Courties, INDOPAC Expeditions produced adults and young 1976; Alldredge et al., 1984). -OT HO* 120* ISO* 140* I50*E • STATIONS 0 Co/onoii 9S philippensis • Rhincok lus nasutus \,ic^ T ■V ; Fig. 4 Composite stations of the Siboga Expedition (1899), the Snellius Expedition ( 1929) end R/V “Alpha Helix" Moro Expedition (1979). Stations ere indicated by small filled circles, Calanoides records by open diamonds, and Rhincalanus records by a large filled circle. Note how positive records are concentrated off southwestern New Guinea. SURFACE TEMPERATURES DURING PLEISTOCENE glacial stages, when sea level was lowered by 100 GLACIAL STAGES to 200m. Dotted shading in the area of Wallacea represents special local conditions that would Figure 5 considers Indo-Australian sea surface have lowered surface temperatures on a seasonal temperatures in the present interglacial and basis. estimated temperatures prevailing during Quinn (1971) argues for increased upwelling Pleistocene glacial stages. General features of in equatorial latitudes of the westernmost Pacific figure 5 are from Webster & Streten ( 1972) and during Pleistocene glacial stages. He notes the the CLIMAP Project (1976). Neither source, existence of fossil guano deposits on equatorial however, allows for the influence of coastal islands lying west of the Gilberts, which.indicates upwelling. the past presence of Isrge colonies of sea birds on The top two panels in figure 5 show present islands now lacking such colonies. Presumably conditions prevailing in the two halves of the during Pleistocene glacial periods, equatorial year. The bottom two panels approximate upwelling in the West Pacific provided the conditions thought to exist during Pleistocene resources to support the now extinct bird -89- APRIL-SPETEf-BER OCTOBER-MARCH IHTEROLACIAl 100° 120° 140° 160° 100° 120° 140° 160° E Fig. 5 Sea surface temperature isotherms, *C, surface currents (slender arrows) and Northeast Trade Winds (thick arrows) In eastern Indo-Australian region. Top two panels show conditions In southern hemisphere winter and summer conditions in the present time and hypothesized for past interglacial stages. Bottom two panels show conditions thought to prevail during Pleistocene glacial stages. Oblique line shading in bottom two panels show areas in which unusually cool (<2PC) surface temperatures may have predominated seasonally and acted 8s a barrier to the passage of mixed layer stenotherms; land area extended to 200m isobath to approximately lowered eustatlc sea level during glacial stages. ( modified from Websteri Streten, 1972; Brinton, 1975). colonies. In general over the past 75000 years, for periods of tens of thousands of years. Bé & fluctuations in the intensity of the trade winds has Duplessey (1976) show that the half been concurrent or preceded fluctuations in the million-year record fer the western Indian Ocean amount of lee stored on continents and wind and the quarter-mi 11 ion-year record for the velocity of the winter trades intensified during eastern Indian Ocean had cold conditions cool climatic staoes of the earth and diminished prevailing for more than half of their respective Airing warm stages (Molina-Cruz, 1977). periods. Van Andel et al. (1967) and Webster & Pleistocene glaciei stages appear to hove persisted Streten ( 1972) believe that cool water entered -90- the Timor Sal during Pleistocene glacial stages PONTELLID SPECIATION PATTERNS based on an intensification of the cool, west Australian boundary current and its more If Wallaces W8S a long-term harrier to psssage of northward penetration. Changes in current stenothermal species of the mixed layer, we intensity during Pleistocene glacial stages have should expect to see evidence of its vicariant role been recorded off South Africa ( Hutson, 1980). in spéciation patterns of locally distributed In the northern hemisphere during Pleistocene species groups. That is, sister species may be glacial winters, the NE Trades probably intens expected to have allopatric or parapatric ified sufficiently to induce coastal upwelling off distributions extending from Wallacea. northwest New Oui nea and the eastern Moluccas. Pontellid copepods are abundant and species rich Webster & Streten ( 1972) suggest that surface in the Indo-Australian region. I have recorded to temperatures off northwest New Guinea ranged dete 69 species in the three principal genera, from 22 to 24*C, while the CLIMAP Project Labidocera, Pontella mb Pontellopsis, 48 (1976) indicates 25 to 27*C In the southern being endemic to the region. Most are or appear to hemisphere winter for this area. Reducing these be stenothermal, and ali live In the upper few values by 3*C, the extent surface temperatures meters of the mixed layer. Up to now I have are lowered in upwelling plumes off New Guinea, examined the systematica and distribution of five would depress winter Pleistocene surface species groups of these pontei lids. With few temperatures to a range of 19 to 24*C, i.e., well exceptions, these species are short ranging and below present-day winter conditions. Assuming Inhabit coasta! or neritlc waters. I have assumed that tne median, 21,5*C, is close to actual surface from their morphologic and geographic temperatures in upwelling plumes of the relationships that allopatric spéciation is the Pleistocene glacial winter, the northern end of principal, and likely the sole, process of Wallacea would be inhospitable to tropical cladogenesis in this family. Hypothesized phylo- 3tenotherm? roughly from October to March. In nenetic relationships for each group based on the southern hemisphere's winter, the West sexually modified apomorphies are shown in Australia Boundary Current would Intensify and figure 6. Circled nodes represent hypothesized theSE Trades might cause coastal upwelling along spéciation events that appear, on the basis of the Sahul shelf. It is reasonable to expect winter present distributions, to have occurred in the surface temperatures of about 20*C In the Timor vicinity of Wallacea. Every group has at least one and Banda Seas, es shown by Webster & Streten apparent spéciation event associated with ( 1972), rendering the southern end of Wallacea Wallacea. About 308 of cladogenesis in the five inhospitable to surface-bound stenotherms groups appears to indicate a past Wallaceae roughly between April and September. barrier. The hypothesized glacial-stage conditions shown The lack of a fossil history precludes direct in the lower two panels of figure 5 would enhance dating of copepod spéciation events. However, two C.philippinensis and R. nasutus population sources of inferential evidence provide a expansions, while depressing populations of yardstick for estimating spéciation rates in stenothermal pontei lids. Stratigraphic evidence coastal to slope-water copepods. One source is a by Bé & Duplessy (1976) indicates that the study of geographical variation in Calanus glacial stages persisted for tens of thousands of helgolandicus s.l. (Fleminger & Hulsemann, years several times during the million years of unpubl.). The second (Fleminger, 1975) is from the Pleistocene. For stenothermal species ranging spéciation patterns in American lineages of across Wallacea, each glacial sequence would Labidocera. C. helgolandicus s.l. in the Black interrupt their distribution and provide an Sea has diverged behaviourally and morph opportunity for the allopatrlc subpopulations to ologically from the Mediterranean ancestor and diverge. appears to have Induced reinforcement of reproductive barriers in the Aegean and Adriatic populations. The Black Sea has had a complex -91- relatively restricted geographica! ranges ( i.e., short-ranged) and tropical or subtropical temperature requirements. Their present distribution relative to closure of the Isthmus of Panama about 3,5 million years ago (Woodring, 1966) suggests that these species groups, virtually the equivalent of genera in better-studied taxa, mery have evolved in less than 3.5 million years. This is similar in duration to mora familiar estimates of rapidly evolving genera. For example, ali evolution in the Oalapagos Islands, including radiation of 13 species of Darwin's finches, occured within 3 to 4 million years (Hickman & Lipps, 1985). Thus the Calanus and Labidocera data suggest spéciation rates falling between IO6 and IO4 years. The geographical distribution of each of these five groups are sufficiently similar that anyone can serve es an example of the others. Figure 7 shows the distribution of the Labidocera Fig. 6 datagrams showing hypothesized phylo pectinata group (Fleminger et al., 1982). It is genetic relationships In pontellld copepod species the most coastal of the five groups, typically being groups Indigenous to the Indo-Australian region. confined to waters inshore of the 100m isobath. Circled nodes represent hypothesized spéciation The extent of shading offshore in the figure is, in events that appear on the basis of present most cases, merely for illustrative purposes, and distributions to have occurred in the vicinity of not intented to depict the actual offshore Wallacea. Cladistic analyses based on sexually distribution of Individual species. Two sets of modified morphology. Species indicated by number sister species converge on Wallacea, L.papuenis are undescribed. 8nd L. carpentariensis, north and south relative to Wallacea, and species #3 and L. carpentariensis, east and west of Wallacea. A history varying through Pleistocene time from prolonged temperature barrier in Wallacea would brackish marine to freshwater-brackish have divided a continuous population into two or (Caspers, 1957). When the Black Sea assumed its more allopatric subpopulations. Similar observ present marine-brackish quality to support a ations can be mate for the other four pontellld Calanus population is not established. Never species groups that have been studied. theless, Calanus could not have survived the Considering the sequence of Pleistocene glacials freshening at the beginning of Wiirm 100,000 and interglacials, reduction of eustatic sea level years ago. Indeed, the most recent successful by about 200m, and surface cooling by coastal colonization from the Sea of Marmara may have upwelling, the history of the Labidocera begun after the end of the most recent glaciation, pectinata group may have been roughly as less than 12,000 years ago. hypothesized in figures 8 A-D. Accepting that the Labidocera in the Americas is represented by cold, surface-water barrier in Wallacea, as 18 species divided among four distinctively discussed above, persisted for thousands to tens of different species-groups (Fleminger, 1975). thousands of years, the opportunity did exist for Two groups are restricted to Atlantic-Ceribbean spéciation of the Isolated populations. coastal-nerltlc waters and two to Pacific coestal-neritic waters. The species have -92- 60* 80* 100* 120' 1W 16Cf £ Fig. 7 Present geographical distribution of the Labidocera pectinata species group, based on localities cited in Fleminger et al. (1982) and new unpublished data. Extent of shading offshore is merely for illustrative purposes and not intended io depict actual offshore distribution of individual species; in most cases offshore distribution is confined to waters inshore of the 100m isobath. Cladogram in lower left shows hypothesized phylogenetic relationships of species and shadings representing ranges of individual species. Circled nodes are hypothesized spéciation events that appear to have occurred in the vicinity of Wallacea. These trinomen are current in the copepod literature and are retained in the present paper since it is not a suitable vehicle to propose nomenclatoral changes. Figure 9 is a preliminary summary of three female sexual characters that differ in the three forms. The scatterdiagram shows the distribution of one varying character, the length of the right side of the last thorace segment, plotted against standard (prosome) body length. The two topmost UNDINULA HYBRID ZONE IN WALLACEA clusters of open squares and crosses represent U v.zeylanica from the Marshalls and Samoa. Undinula vulgaris^ a species complex within The cluster of open circles below represent the family Calanidae that has a Calanus -like typica , the continental form from Indian and role, ecologically, in equatorial neritic waters East Pacific coastal localities. The intermediate circumglobally. The systematica of Undinula Uv.giesbrechtf is represented by filled vulgaris s.l. at the species level ere largely squares, filled circles, and filled triangles lying Incomplete. Preliminary studies by Yervoort intermediate to' U. v. typica and U v.zey Ianica. (1946) that were expanded by an unpublished The Atlantic population aiso assigned to study of Fleminger & Hulsemann indicate a zone of U. v. typica by previous authors, though in high variability in U vulgaris in the area o. error in my judgement, is represented by the Wallacea. open, inverted triangles below. Three subspecific forms of Undinula Th8 drawings on the left depict the adult female vulgaris s.l. have been recognized in the Indo- right fifth pediger-bearing thoracic segment, and Pacific: I. Uv. zeylanica inhabiting coastal the distribution of cuticular glands associated waters around oceanic islands; 2. U. v. typica with one of the sites on which the male occurring in continental neritic waters in the East spermatophore Is cemented. U. v.zey Ianica at Pacific, off Asia, and East Africa; and 3. the top left has columnar cells arranged U v.giesbrechti, a variable population largely perpendicular to the articulation with the fourth concentrated in Wallacea and more or less pediger-bearing thoracic segment. U.v.gies- intermediate to U. v.zeyIanica and U v. typica. breebti, second from the top, has numerous -93- Fig. 8 Hypothesized sequence of spéciation in the Labidocera pectinata group. Continental barriers ara based on major land drainage systems that would interrupt distributions of coastal water species during glacial stages and melt periods leading into an interglacial stage. Seasonal barriers refer to the cooling effects of probable seasonal upwelling during the northern hemisphere winter and the cooling effects of the West Australia Boundary Current, es well as possible coastal upwelling In the southern hemisphere winter as discussed in the text. Shadings are identified in figure 7, except that the vertical lines in panel A refer to an ancestral precursor of L. pectinata. glands scattered across both the fourth and fifth has columnar glands distributed along the dorsal pediger-bearing thoracic segments. Indo-Pacific border of the fifth pediger-bearing segment. The U v. typica, third from the top, has a few glands smaller figures on the right show the fifth scattered over the fifth pediger-bearing segment. pediger-bearing thoracic segment and genital The Atlantic form of Uv. typica , bottom left, segment in the left lateral and dorsal views, -94- U. v.zey Ian ica at the top, U. v. giesbrechti In patterns suggesting that Wallacea constituted a the middle, and the Indo-Pacific Uv. typica geographic Carrier in the course of their below. cladogenesis. The barrier is conceived in terms of It is tempting to regard U v.giesbrechti as a extensive chilling of Wallacean surface waters hybrid population, the consequence of secondary during Pleistocene glacial stages and Is based on contact between the oceanic U. v.zey ianica the avoidance of upwelling plumes by present-day transported westward by the North and South stenothermal pontei lids. Equatorial Currents and the Asian U. v. typica. Further biological evidence Is provided by the In Wallacea, hybridization between U. v. typica apparent hybrid swarm of Undinula in Wallacea. and U. v.zey ianica probably would have spread Though the Undinula study would benefit from after warming of surface waters in the present additional data that may suggest an interpretation Interglacial period. other than the one suggested above, the available results provide noteworthy support for the Wallacea hypothesis. This singular example of an DISCUSSION AND CONCLUSION east-west gradient of morphological change in sexually modified characters centers dlreclty on To summarize, Wallacea, the Pacific-Indian Wallacea. Moreover, similar patterns of tropical seaway lying between Celebes and New morphological diversity have not been observed Guinea, was greatly reduced in area during elsewhere in Undinula or in any other genus of Pleistocene glacial stages when eustatic sea level calanoid copepods. fell 100 to 200m. Coastal upwelling prevalent Biological evidence is aiso provided by the today in highly localized areas off western New otherwise unexplained failure of many lowland Guinea was probably more extensive during terrestrial plant and animal species to disperse Pleistocene glacial stages and apparently provided across Wallacea either from Asia eastward or conditions suitable for the evolution of an endemic from Australia / New Guinea westward, the upwelling species of Catenoides. Paleo- original basts for proposing the biogeographical temperature estimates of surface waters in the boundaries between Borneo and New Guinea. glacial stages modified by likely upwelling effects This hypothesized Wallacean barrier completes suggests a low of about 21’C in the northern half the sequence of geographical barriers in of Wallacea during the northern hemisphere equatorial latitudes that began in Miocene- winter and about 20*C in the southern half of Pliocene time to Interrupt Tethyan pelagic Wallacea during the southern hemisphere winter. distributions and generate the present-day Stratigraphic evidence Indicates 1hat these glacial biogeographic patterns of equatorial pelagic stages persisted for es long as tens of thousands of species of the mixed layer. The Wallacea barrier years. hypothesis may be tested by stratigraphic studies Five pontellld species groups show spéciation in eastern Indonesian sees, and by feeding, Fig. 9 Undinula vulgaris s.l., adult female. Scatter diagram showing length of the right fifth pediger-bearing thoracic segment (ThV) plotted against standard body length ( prosome) in six geographical populations. Open squares and crosses represent subspecies ceylanica from Pago Pago and the Marshall Islands, respectively. Filled triangles, filled circles and filled squares represent subspecies giesbrechti from Wallacea north and south of equator, respectively. Open circles represent subspecies typica from Indian Ocean and eastern Pacific. Inverted open triangles represent subspecies typica trom Atlantic Ocean. Small figures on the left are right lateral views of ThY and genital segment; distribution of cuticular glands and openings shown es columnar structures and dots. Shaded area indicates storage of glandular products. Small figures on right are left lateral and dorsal views of ThY and genital segment. From the top down, subspecies zeylanica, giesbrechti and typica; the fourth figure down on the left is subspecies typica from the Atlantic. -95- 0.60 0.55 D n □ □ a Q 0*0 Q ö> 0 0.50 ö’di’ti X * X XXX # XX D 4 O # XXX# a o X x# #X x 0.45 X x#*#* * A A a X X K x x jfx £ a X AA* à X A AA 4 4 o A * £ AA AM*é y A Ajf I <*0 «VA AA A 1-- j ’ X a o • ó,ó)4 O A o mA»^o ooo&ooa I i> OA O tfÓ1 Ó'^c'o O O <5* QtÇP’o’Atf» o o o o 0.30 o Pogo Pogo X Marshalls Naga SIIB-62 E. Pacific Indian Atlantic Naga 0.25 No. Pacific So. Pacific JL 1.60 1.80 2.00 2.20 2.40 PROSOME (mm) -90- reproductive and growth studies of pontellid REFERENCES stenotherms at temperatures ranging below 26*C. The evolution of tropical copepods species that -ALIDREDGE, A. L.. B. H. ROBISON. A. FLEMINGER. J. have been analyzed in detail, i.e., the genera J. TORRES. J. M. KING & W. M. HAMNER, 1984. 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Ecological Studies, -97- Ana/ysis and Synthesis, J. Springer Verlag, Snellius Expedition. XV. The bathypelagic Copepoda Berlin : 339-347. Calanoida of the Snellius Expedition. 1.Families -REMINGER, A. & K. HÜLSEMANN. 1974. Systematics Calanidae, Eucalanidae, Paracalanidae and Pseudo and distribution of the four sibling species comprising calanidae. Temminckii, 8 : 1-181. the genus Pontellina Dana (Copepoda, Calanoida). -WEBSTER, P. J. & N. A. STRETEN. 1972. Aspects of Fish. Bull., 72(1): 63-120. late Quaternary climate in tropical Australasia. In: D. -FLEMINGER, A., B. H. R. OTHMAN & J. G. GREEN Walker (ed.) Bridge and barrier: the national WOOD, 1982. The Labidocera pectinata group: an and cultural history oF Torres Strait. Aust. Indo-West Pacific lineage of planktonic copepods with nain. Univ., Canberra, Res. School Padf. Stud. Puhi. descriptions of two new species. J. Plankt. Res., B6./3 : 39-60. 4: 245-270. -WOODRING, W.P., 1966. The Panama land bridge as a -FROST, B. & A. 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Cah. O.R.S. T.O.ii. Oceanogr., 14: 177-199. -GUINN, W. H., 1971. Late Quaternary meteorological and oceanographic developments in the Equatorial Pacific. Nature, 229 : 330-331. -RAVEN, P. H. & D. I. AZELROD, 1972. Plate tectonics and Australasian paleobiogeography. Science, 176 : 1379-1386. -SCOTT, A., 1909. Copepoda of the Siboga Expedition. Parl.l. Free-swimming, littoral and semi-parasitic Copepoda. Siboga Exp. tlonogr., 29a : 1-323. -SMITH, S. L., 1982. The northwestern Indian Ocean during the monsoons of 1979: distribution, abundance and feeding of zooplankton. Deep-Sea Res., 29 : 1331-1353. -VANANDEL, T.H., G.R. HEATH, T. C. MOORE &D.F. R. MCGEARY, 1967. Late Quaternary history, climate and oceanography of the Timor Sea, Northwestern Australia. Am. J. Sei., 265 : 737-758. -VERVO0RT, W., 1946. Biological results of the -90- THE STOMUMD FISH GENUS EUSTOMIAS AND THE OCEANIC SPECIES CONCEPT ROBERT H. GIBBS JR National Museum of Natural History. U.S.A. INTRODUCTION valid only 37 of the 66 names that had been decribed ( Morrow & Gibbs, 1964). It would seem We cannot study biogeography, even in the that workers were convinced that it was unwise to simplest way, unless we know what species we are describe new species, for in the 50 years from working with. It is even better, of course, if we 1933 to 1983 only ten were described, ali from know their phylogenetic relationships. It is my the Indo-Pacffic and ali vulld. contention that we are a long way from knowing In 1983 the bubble burst when the first of a what species really exist in the oceanic series of papers was published by myself and environment. Workers are taking existing taxon co-workers based on our realization that the omic works for granted, and this is a mistake. We conservative approach had been wrong. In one must look harder at the organisms that we work subgenus, Nominostomias, where eight species with, examine more characters, and make an previously had been recognized as valid, we attempt to recognize the several species that so restored five species from synonymy and often are hiding under a single name. There ere described 25 new ones (Gibbs, Clarke & Gomon, more species out there than we realize. 1983). Papers now in press or contemplated soon will bring the number of Eustomias species to well over a hundred. THE GENUS EUSTOMIAS What has happened is that subtle differences that we once believed were variations in a single I will illustrate my point by a consideration of the species are being found to be repeated, to occur in mesopelaglc, predatory fishes of the genus both sexes, and to have geographic integrity. Eustomias. The species of Eustomias are Figure 1 shows the barbels of four Atlantic and seldom taken in numbers in the gear most six Pacific species of Nominostomias, ali of commonly used for sampling the oceanic mid which have two terminal bulbs and a single, waters, and it has taken a long time to obtain simple terminal filament. In 1964,1 would have series that are sufficient to show variation or recognized these es only one species (/V consistency in morphological characters. As it bibulbosus), sceptical that such minor differ turns out, while groups within Eustomias can ences could be more than intraspecific variation. be recognized by a number of different kinds of Five more species, three Atlantic and two Pacific, characters, the species within these groups are of the same subgenus are shown in figure 2. These recognized almost entirely by the structure of the aiso have a single central filament, but with side barbel that hongs from their chin. branches well developed. In 1964 I considered In the 45 years from 1888, when the genus and them to be the same species ( N. bibulbosus) as first species were described, until 1933, 64 the previous ten. A third group of two-bulbed nominal species of Eustomias were described, species is shown in figure 3. These have several ali of them from the Atlantic. Then, in 1939, filaments arising together from the terminal Beebe & Crane questioned the validity of a number bulb. I considered the two described Atlantic of the species and reduced several of them into species to be one in 1964. Now we recognize three synonymy. I followed suit In 1964, not believing Atlantic and five Indo-Paclflc species, and one that that so many minor variations in barbel structure occurs In both the Atlantic and the Indo-Pecific, could indicate species status, and I recognized 8S the only species in the subgenus to do so. Thus, -6fr- Fig. 1 Barbels of Eustomias (.Nominostomias) species with simple terminal filaments. Left, Atlantic species--top to bottom: E.ùiùufùosus, E. mier aster, f.austrat/anticus, f. bituberatus. Right. Pacific species — top to bottom: £. inconstans, £. appositus, £. orientalis, E.bibulboides, £ australensis, E.bituberoides. Fig. 2 Barbels of Eustomias ( Norn isos tom fas) species with branches from a central filament Left, Atlantic species — top to bottom: E arborifer, E.grandibulbus, E bimargaritatus. Right Indo-Pacific species— upper, E crossotus ; lower, E.bimargaritoides oi lo \ I Fig. 3 Barbels of Eustomias^ Nominostomias.) species with several filaments arising together. Left, Atlantic species — top to bottom: E.melanonema, E.melanostigma, E.kreffti, E. posti. Right, Indo-Pacific species — top to bottom: £.melanostigmoides, E.mu/tifi/is, £.medusa, E.ùerte/seni, £. su itiensis -102- what I would hove considered to be two species in the taxonomic decisions based on barbel morph 1964 ere recognized today es being 24. ology. Some, but not ali the Pacific species appear We were able to show that each of the well- to have separate ranges, (but the Pacific has not represented forms differed from each other in been sampled nearly as well as the Atlantic). relative growth and size of the barbel end/or one It should be noted that only one (M or more of its parts, including each of the bulbs, melanostigma) of the 38 species in the the distance between them, and the terminal subgenus Nominostomias occurs in both the filament. By inference, the poorly represented Atlantic and the Indo-Pacific. In fact, of the forms that showed such differences were aiso approximately i IO species of Eustomias that considered species. The fact that the Atlantic we currently recognize, only 12 (Including species turned out to have almost entirely N. melanostigmi) have not yet been shown to separate geographic ranges (Fig. 4) reinforced have slight, but consistent differences in the 100° 80° 60° 40° 20° 0° 20° 40° 20° 0° 20° 40° Fig. 4 Distributions of the 11 Atlantic species of Eustomias( Nominostomias). 1, E. bibulbosus ; 2. E.micraster ; 3. E bituberatus; 4. E.ausirat/antfcus ; 5. Ebimargaritatus ; 6. Earborifer ; 7. E.grandibulbus ; 8. E.melanostigma ; 9. Emelanonema ; IO. £. kreffti -, 11. £posti. The only species with a range broadly overlapping that of other species Is Earborifer(6). -103- Atlantic and Indo-Pacific. We have not examined can affect the phenotypic expression of 11 of these species carefully, end I predict that characters. I know that polymorphism occurs. inter-oceen differences will be found in eli or Until these things can be demonstrated, however, most of them. Even within oceans, we are finding we should recognize discrete morphological complexes of similar species where only one was entities as species. In doing so, I believe we will recognized before. Circum-central tropical be right most of the time. species would appear to be rare or non-existent. The only truly clrcumglobal oceanic species of Eustomias may be E trewavasae which CONCLUSION inhabits the southern Subtropical Convergence. A taxonomic decision to cali similar forms The genus Eustomias is not an isolated case. species is easier to accept, at least in practical Most oceanic organisms ere in need of terms, for allopatric forms than for syntopic discriminating taxonomic study. We should be forms. A cose in point involves two Atlantic suspicious of the many so-called species that have species, Eustomias filifer and E mono circumglobal or circum-central tropical distrib dactylus*'^ I synonym Ized In 1964 and now utions. In ali probability they are complexes of consider valid again. They are obviously closely subtly distinct species. Even species that have related, differing slightly but consistently in broad distributions within oceans should be barbel structure (see Morrow & Gibbs, 1964), suspect. We should take our clues from the and both have been taken in the same areas in the restricted distribution patterns that more and Atlantic from 40'N to 40*S. Off Bermuda, the two more taxonomists are describing for their finely have been taken in the same net haul, together discriminated species. What one set of organisms with a third, undescribed species. This situation displays can be expected and should be sought in suggests the possibility of intraspeciffc poly others. morphism, but ali three forms are distinct, and I prefer to cali them species until evidence to the contrary is forthcoming. REFERENCES The species concept expressed here is typological, based entirely on morphology. No -BEEBE, W. & J. CRANE, 1939. Deep-sea fishas of genetic, biochemical, or physiological evidence is the Bermuda Oceanographic Expeditions: Family available. As far as I know, no live specimen of Melanov.tomiatidae. Zoologica, 24{2)\ 65-238. Eustomias^ ever been taken, end no breeding -GIBBS, R. H.. Jr.. T. A. CLARKE 8. J. R. GOMON. or other experiments have been undertaken. The 1983. Taxonomy and distribution of the stomlold modus operandi is to take character variation into genus Eustomias (Melanostomiidae), I: Subgenus account as well es possible, and when morph Nominostomlas. Smithson. Contr. Zooi., (360) : iv, 139 pp. ological gaps remain, the distinct entities are -MORROW, J. E.. Jr. & R. H. GIBBS, Jr.. 1964. considered species. If a gap involves only a single Family Melanostomiatidae. In: Fishes of the Western character, the decision should be the same. When North Atlantic. Hem. Sears fetn mar. Ros., i the different morphologies are allopatric, such (4): 351-511. decisions are not too difficult to eccept, but when they are syntopic, there will be more scepticism. Whether or not this simple criterion is acceptable to others, It works, and I believe that the entities that it defines should be recognized formally and described as species. Unless a name is available, workers are unlikely to pay any attention to the entity in question or to look into the reasons or circumstances for the occurrence of such entities. I know that environmental factors -104- THE GULF OF AQABA. A ZONE OF GREAT BIOLOGICAL INTEREST J. E A. GODEAUX Laboratory of marine Biology, University of Liège, Belgium The Red Soa, a rather young see, is connected to 1979; 1985). Ritteriella amboinensis is the Indian Ocean through the strait or Bab el usually a rare species but it can be considered es Mondob ot 12*40'N. It is entirely located in a characteristic of the Oulf, and Brooksia ros very arid, hot and dry area. Owing to the increase trata with a low catch frequency in the equator In salinity, life conditions become harder In Its ial zone is rather abundant here. Doliolina two northern appendages, the shallow Gulf of Suez indicum, an Indo-Pacific species, is regularly (depth < 60 m) and the deep Oulf of 'Aqaba. At the observed in the samples. On the contrary, Salpa entrance of this Oulf, the narrow sill of Tiran cylindrica, the commonest species in the oceanic (252m) rises between two > 1200m deep tropical waters, is found in the Red Sea proper trenches, with steep slopes. but it is practically absent in the Oulf (a single Ecological conditions prevailing in the Oulf of catch). The ssme is true for Salpa maxima (S. 'Aqaba are known thanks to the Oats Collecting tuberculata) often collected by the Manihine Program In the Oulf of Elat ('Aqaba) (D.C.P.E.) Expedition (1948-49) (Yan Name, 1952) and initiated by the Heinz Steini Marine Biology now very rarely found. Thalia rhomboides Is Laboratory In 1974 (Reiss & Paperna, 1975; rare, except locally. 1976; Shilo & Cohen, 1979; Shilo & Paperna, 3) The occurrence of ecological races: Three 1977). Surface temperature varies between 20*C species of Cladocera are known from the northern in the winter and 27*C in the summer season; at pert of the Red See: Evadne tergast inoi. Oulf of about 150m temperature is 2 PC. Salinity in 'Aqaba), Evadne spinifera (main basin) and creases from the entrance owing to evaporation, Penilia avirostris (Oulf of Suez). The reaching 40.8°/oo and more in the depth (below specimens of these three species are in external 500m). There ara no significant thermocline and morphology strictly similar to the specimens helocline. Waters are oligotrophic but well from other parts of the world, as proved by the oxygenated; the primary production is low. scanning microscope (Meurice, 1983; Maurice & Thaliacea, although collected at ali depths, ara Dauby, 1983). Probably, the diffères are mainly caught with closing nets In the upper limited to the physiological level. As far es the layers, from 200m to the surface (>21*C). Thaliacea are concerned, the same considerations Doliolums and salps are only found, as pyrosomas may be evoked: e.g. the morphology of the were never recorded from the Red Sea. The specimens of Thalia cicar and Doliolum thaliaceen fauna is a mixture of Indo-Pacific and denticulatum are fully identical to those from ubiquitous species (Table I). Although devoid of both Atlantic and Indian Oceans. endemic species, this fauna exhibits original Some species are truly tropical ( Thalia features. cicar, Ritteriella amboinensis). Others, 1) Dwarfism shown by many species: e.g. the rather tolerant to temperature variations, ( Iasis phorozoids and gonozooids of Doliolum zonaria, Brooksia rostrata) became adapted denticulatum reach a length of 3- 4mm ( instead to severe ecological conditions. Some species were of 5mm and more In Atlantic specimensX personal not successful, as they occur only rarely, e.g. observation). Salpa cylindrica and Salpa maxima while 2) The remarkable presence of salp species Thalie democratica and Salpa fusiformis rather uncommon in other sees (Oodeaux, 1978; are completely lacking. -105- Table I The thaliac88n fauna of the Red Sea, Oulf of 'Aqaba, Oulf of Aden, and the Arabian Sea Thaliacea Red Sea Oulf of Oulf of Arabian N S ’Aqaba Aden Soa Cyclosalpa pina. sewelli » • Cyclosalpa floridana » Cyclosalpa bakeri* * Brooksia rost ratti* * * » Salpa maxima/* » * Salpa cylindrica « * • • * Ritteriella amboinensis • * » « • Ritteriella picteti « Metcalfina hexagona « • Iasis zonar id* » * • • Thalia rhomboided* * * * « Thalia cicar * • « * • Thalia oriantalis •• Pegea confoederata « » • Doliolina muelleri Doliolina krohni * * * • Doliolina intermedium ? Doliolina indicum • ft « • * Doliolum denticulatum « * • « » Doliolum nationalis * « • « Dolioletta gegenbauri * ? * * tritonis Pyrosoma spinosum » • Pyrosoma agassizi « (Compiled from different sources, Oodeeux, 1985) The fauna of the Red Sea is different from that of 'Aqaba, Is the result of selective ecological the Eastern Mediterranean; as a matter of fact pressures. there is no proof of former connections between the two seas. From the beginning, the fauna of the Red Soa was of Indo-Pacific origin but it is REFERENCES somewhat impoverished: eg. Thalia orientalis, Metcalfina hexagona and the pyrosomas -GOOEAUX, J., 1978. Les populations de Thaliacés du present in the Oulf of Aden and the surrounding Golfe d'Etat. Bull. Soc. r. Sei. liège. 47 : areas are absent in the Red Sea. Pegea 386-389. confoederata is present only in the southern -600EAUX. J.. 1979. Thaliacea from the Red Soa. the part of the Red See. Oulf of Aden and Ute western Indian Ocean. Ann Is Soc. r. zoo/. Belg.. 109'. 117-119. Obviously, the fauna of the northern Red See, -GOOEAUX, J., 1985. The thaliacean faunas of Ute exemplified by the Thaliacea living in the Oulf of -106- Mediterranean and the Red Soa. In: R. van Grieken & R. Wollast (eds) Proc. Progress in Belgian oceanographic research. Brussel: 451-460. -MEURICE, J. C.. 1903. Morphologie et ultrastructure comparés des appendices et des difTérenciations tégumentalres chez les Cladocères et quelques autres Entomostracés. Thèse doct. Univ. Liège, 1,2: 136pp., 179 figs. -MEURICE, J. C. 8. P. DAUBY, 1983. Scanning electron microscope study and computer analysis of taxonomic distances of the marine Podonidae (Cladocera). J. Plankton Ros., 5: 787-795. -REISZ Z. & I. PAPERNA. 1975. Fourth report of the H. Steinia marine biology laboratory Elat. DCPE- Data collecting program in the Gulf of fiat. Rep., /: 46-55. -REISZ. Z. & I. PAPERNA. 1976. Fifth report of the H. Stelnltz marine biology laboratory Elat. DCPE- Data collecting program in the Gulf of Elat Rep., 2 \ 22-68. -SHILO, M. 8, I. PAPERNA. 1977. Sixth report of the H. Steinilz marine biology laboratory Elat. DCPE- Data collecting program in the Gulf of Elat. Rep.. J: 31-54. -SHILO, M. 8, Y. COHEN. 1979. Seventh report of the H. Stelnltz marine biology laboratory Elat. DCPE- data collecting program in the Gulf of Elat. Rep., 4: 22-25. -VANNAME, 6.. 1952. The Manihine expedition to the Guir or ‘Aqaba 1948-1949.- Tunicata. Bull. Brit. Mus. nat. Hist., (Zool.) /(8): 215-220. -107- SIZE SPECTRA IN MESOPELAGIC FISH ASSEMBLAGES* RICHARD L. HAEDRICH Memorial University of Newfoundland, Canada. INTRODUCTION production for the different areas using rules derived from considerations of allometric scaling. The utility of allometric scaling of biological processes h8s long been obvious to physiologists (Colder, 1984), but opplication in ecology has METHODS only been appreciated rather recently (Peters, 1983) . Size spectre have shown significant The data were derived from mesopelagic fish promise over taxonomically based approaches samples taken in over 1,000 Isaacs-Kidd mid (Sheldon et al., 1977; Sprules & Holtby, 1979; water trawls made throughout the Atlantic Ocean Ooriover & Huntley, 1980), so much so that a from Iceland to the Southern Ocean (Backus & SCOR working group hss recommended this as an Craddock, 1977). Species lists were generated for important research area (Matthews et al., each of 19 faunal regions, and the aggregate 1984) . weight of each species wa3 divided by the total Studies of size spectra in the ocean emphasize number of specimens in each region to give the the small particles that are readily measured mean size for that species, expressed 83 log to the using a Coulter Counter (Platti Denman, 1978). base two. Estimates of primary production for Little work has been done involving pelagic each faunal region were obtained by overlaying organisms much larger than Copepoda. The the regions on the primary production chart of biomass in different size classes is said to be Koblentz-Mischke et al. (1970) and integrating approximately equal across the full spectrum, using a Hewlett-Packard digitiser. even though regional differences have been noted Size spectra are usually expressed graphically (Sheldon et al., 1972). Studies in lakes (Sprules es a frequency distribution, and are not easily & Knœchel, 1984) show a pattern which is quite quantified. To overcome this difficulty, the "spike/”, i.e. there is fsr more biomsss in certain biomass spectrum Is here expressed as a fractal size classes than in others. The assumption (Mandelbrot, 1977), a measure useful for the continues to be that size spectra in oceanic analysis of complex structure (Bradbury et al., assemblages are quite flat and that the biomass 1984; Morse et al., 1985). To calculate the distribution Is relatively uniform from class to fractal, the log of the distance along the curve of class (Conover, 1979). the spectrum is divided by the log of the distance The purpose of the present study, part of a along the abscissa over which the curve is plotted. larger work on size structure in marine No special ecological meaning should be attached to communities, is to compare size spectra bssed on this use of a fractal; applied to size spectra it is the mesopelagic fish assemblages of faunal regions an index only. proposed for the Atlantic Ocean (Backus et al., The fractal dimension of a spectrum is 1977). Our concept is that pulses of production conceptually appealing. The dimension is by the smaller size classes in a system propagate independent of scale, i.e. the same fractal along the size spectrum as spikes of varying dimension is obtained whether one looks at a very amplitude (see Silvert & Platt, 1980). By small portion of a range or the entire range itself extension we argue that the more pronounced the (Mark, 1984). This means that the fractal pattern of seasonal primary production, the more dimension of a spikey distribution will indicate "spikey” the spectrum will be. A second objective spikeness whether a small portion (e.g. meso is to calculate the potential midwater fish pelagic fishes) or the entire spectrum (e.g. * NlCOS Contribution No. 90, supported by a grant from NSERC. -108- -'î -2 0 2 4 6 SIZE CLASS, L0G2 (MEAN WEIGHT) SIZE CLASS, L0G2 (MEAN WEIGHT) Fig. 1 Spikey and smooth biomass spectra based on Fig. 2 Intermediate biomass spectra based on oceanic mesopelagic fishes. Top: Atlantic Subarctic oceanic mesopelagic fishes. Top: Azores-Britain region, 53 stations (fractal dimension = 1.41). province, 105 stations (fractal dimension = Bottom: Northern Sargasso Sea province in the 1.30). Bottom: Ouinean province, 55 stations fall, 47 stations ( fractal dimension =1.15). ( fractal dimension = 1.26). nan noplankton to whales) is examined. We have dividing the calculated production figure by the determined empirically that 8 purely spikey total area swept by the trswl in each region. biomass spectrum (ali biomass in one sizeclsss) will have a fractal dimension of two, and a purely smooth one (biomass the same in ali size classes) RESULTS AND DISCUSSION will have a fractal dimension near one. There is no allometric relationship that Biomass size spectra for mesopelagic fishes in the equates production directly to size, so the Atlantic range from the extremely spikey one production:biomass (P/B) relationship was characteristic of the Subarctic region to the very calculated instead. For fishes, this relationship is: smooth one of the northern Sargasso Sea in fall P/B = 0.44 W-0-26 (Banse & Mosher, 1980). (Fig. 1). The pattern follows that described for The equation is rearranged and separate much smaller particles, with the flattest spectra calculations are made for each size class and occurring in the tropics and the most spikey summed to give relative annual production per towards the poles (Conover, 1979). As with the station. Production is aiso expressed as an small particle spectra, areas Intermediate in absolute value, gm fish/ha/yr, arrived at by condition between the central gyre and the higher -139- Table I Faunal regions based on mesopelagic fish distributions in the Atlantic Ocean: number of stations (IKMT), estimated primary production (gm C/m2/yr), fractal dimension, relative mesopelagic fish production based on the allometric relation, estimated absolute annual mesopelagic fish production (gm/ha/yr), and area ( 105km2). Province sta prim fractal rei obs area prod dimension prod prod Subarctic 53 426 1.41 230.6 71.1 45.9 Western Mediterranean 31 270 1.37 168.5 39.4 3.7 Ouineon 55 189 1.26 62.7 17.9 77.4 Slope Water 54 278 1.36 85.5 16.1 4.9 Azores-Brttatn 105 200 1.30 40.8 14.4 29.8 Caribbean 52 210 1.29 69.6 12.7 18.8 N.North African 53 129 1.22 34.8 11.3 15.4 Amazon 73 215 1.28 39.2 9.9 42.0 S.North African 72 186 1.22 26.4 7.6 37.4 Northern Sargasso 86 77 1.32 27.6 7.2 32.8 Mediterroneon Outflow 42 200 1.25 15.3 5.6 12.3 Eastern Mediterranean 35 200 1.34 35.4 5.6 11.7 Antillean 47 215 1.19 19.3 5.4 12.4 South Atlantic 94 70 1.24 12.0 5.2 101.6 Southern Sargasso 77 155 1.21 12.3 3.2 29.0 latitudes show intermediate spectra (Fig. 2). The fractal dimension can be used as a predictor Thus, biomass spectra are not flat everywhere in of fish production, although the relationship is not the ocean; in fact, they are little different from linear (Fig. 3 .Tablet). Both this relationship and the spectra shown for plankton in lakes (Sprules the regression for the linear semi-log &Knoechel, 1984). relationship (log P = 9.08 F - 7.88) are Based on the results of other studies (e.g. significant (p<.01). This result means, 8S is Bradbury & Reicheli, 1983), it was expected that observed, that spikey biomass spectra the fractal dimensions of the biomass spectra characterise regions of high seasonal production. would displey either one or only a few discrete The fractal dimension offers an approach to the values. This situation would have been in keeping difficult problem of determining levels of with the traditional characterisation of tropical, production Tor an assemblage, and is particularly subtropical, temperate and polar oceans. This is useful Tor comparative studies. It could aiso be not the case. There is a smooth range of fractal used to predict production over the entire size dimensions from 1.2 in the South Atlantic and spectrum in an area. southern Sargasso Sea to 1.4 for the Subarctic A fundamental concern is whether the (Tablet). In regard to the ecological relationships production values based on the allometric relation implied by the varying sizes of animals have any bssls In reality. This is difficult Io test, inhabiting them, the faunal regions grade rather because measurements of actual production have uniformly from the central gyre condition to that not been made. It is encouraging that measured of the highly seasonal northern ocean. The values of primary production track those for fish approach de-emphasizes clear distinctions production very well (Fig. 4, Table I). The chart between faunal regions, as does the recent faunal of production based on size spectra (Fig. 5) study of McKelvie ( 1985). resembles the familiar chart of primary -HO- oz zoo 1 .__i- I 26 130 134 160 201 FRACTAL DIMENSION RELATIVE F*SH PRODUCTION Fig. 3 Relative mesopelagic fish production based Fig. 4 Scatter plot of the relationship between on the allometric relation P/B=0.44W'0-26 es a relative mesopelagic fish production and primary function of fractal dimension for faunal provinces production, gm C/m2/yr; r=0.83, p<.01. in the Atlantic; r=0.80, p<.01. Includes only Includes only regions with more than 30 stations. regions with more than 30 station. production for the Atlantic. Lowest values are found iii the central gyres, and the highest values are in high latitudes and special areas such as the 100W 80 60 40 20 OE 20 40 Mauritanian upwelling. The absolute values of mesopelagic fish production (Table I) are unrealistically low, with a total annual production of only about 50,000 tonnes predicted for the entire North Atlantic basin. But the calculations are based on the standing stock biomas os determined from the Woods Hole IKMT surveys, and independent estimates from the same regions suggest these data H AILANliC It MPI RAII are low by at least two orders of magnitude (Qjosaeter & Kawaguchi, 1980). If the absolute N Ali AN I IO SUBTROPICA) production values are multiplied by 100, the new values seem much more in line. For example, the MAUPIIANIAN I'PWIM INO average annual catch of lanternfish in the South Ali AH 11C UTOPICA) African purse seine fishery (9,450 tonnes) would then be about 9* of the annual mesopelagic fish production calculated here for the somewhat 6 I? gm/ha/yr ) comparable Mauritanian Upwelling region, and --- I? 18 gm/ha/y< S Ali AN MC SUBIROPICAI about 12* of the production calculated for the Slope Water. REFERENCES Fig. 5 Absolute mesopelagic fish production, bssed on the allometric relation of Banse & Mosher -BACKUS, R. H. & J. E. CRADDOCK, 1977 (unpubl. ( 1980), by faunal province in the Atlantic ocean. m.s.). Data report for Atlantic pelagic zoogeography. Data from table I ; boundaries from Backus et al. Woods Hole Ocean. Inst. Techn. Rep., (1977). -111- WHOI-77-4: 85 pp. Press, New York. -BACKUS. R. H.. J. E. CRADDOCK. R. L. HAEDRICH 8* -PLATT,T. & K. L. DENMAN. 1978. The structure of B. H. ROBISON. 1977. Atlantic mesopelagic zoo pelagic marine ecosystems. Rapp. Proc. -verb. geography. Mem. Sears Fdn mar. Res., /(7) : Reun. Cons. int. Explor. Mar, 173:60-65. 266-286. -SHELDON. R.W., A.PRAKASH 8» W.H.SUTTCLIFFE, Jr., -BANSE, K. & S. MOSHER, I960. Adult body mass 1972. The size distribution of particles in the ocean. and annual production/biomass relationships of field timnol. Oceanogr., 17 : 327-340. populations. Seoi. Monogr., 50 (3): 355-379. -SHELDON. R. W., W. H. SUTTCLIFFE, Jr. 6, M. A. -BRADBURY, R. H. & R. E. REICHELI, 1983. Fractal PARANJAPE. 1977. Structure of pelagic food chains dimension of a corai reef at ecological scales. Mar. and relationship between plankton and fish production. Eco!. Prog. Ser., IO: 169-171. J. Fish. Ros. Bd Canada, 34 : 2344-2353. -BRADBURY. R. H.. R. E. REICHELI 6 D. 6. GREEN, -SILVERT. W. & T. PLATT. I960. Dynamic 1964. Fractals in ecology: methods and inter energy-flow model of the particle size distribution pretation. Mar. Eco/. Prog. Ser., f t : 295-296. in pelagic ecosystems. In: W. C. Kerfoot (ed.). -CALDER, W. A., III, 1984. Size, Function, and Evolution and Ecology of Zooplankton Life History. Harvard Univ. Press, Cambridge, MA. Communities. Univ. Press New England : 754-763. -CONOVER, R. J., 1979. Secondary production as an -SPRULES. W. G. & L. B. HOLTBY, 1979. Body size and ecological phenomenon. In: S. van der Spoel & A. C. feeding ecology as alternatives to taxonomy for the Pierrot-Bults (eds). Zoogeography and Diversity study of limnetic zooplankton community structure. oFPlankton. Bunge Sclent. Puhi., Utrecht: 50-66. J. Fish. Ros. Bd Canada, Jtf(11): 1354-1363. -CONOVER, R. J. & M. E. HUNTLEY. 1980. General -SPRULES. W. G. & R. KNOECHEL. 1984. Lake rules of grazing in pelagic ecosystems. In: P. G. ecosystem dynamics basd on functional represent Falkowski (ed.). Primary Productivity in the Sea. ations of trophic components. In: D. G. Meyers 8. J. Environ. Sei. Pes., t9 . Plenum Press, New York R. Strickler (eds.). Trophic Interactions Within : 461-485. Aquatic Ecosystems. Amor. Ass. Adv. Sei. Sei. -6J0SAETER, J. 6 K. KAWAGUCHI. 1980. A review Symp. 85: 383-403. of the world resources of mesopelagic fish. F AO Fish. Tech. Pap., /PJ: 1-151. -KOBLENTZ-MISHKE, Û.J., V.V. VOLKOV INSKY 6 H.G. KABANOVA. 1970. Plankton primary production in the world ocean. In: W. S. Wooster (ed.). ScientiFic Exploration oF the South Pacific. Nat. Acad. Sei.. Wash. : 183-193. -MANDELBROT. B., 1977. Fractals: form, chance, and dimension. Freeman, San Francisco. -MARK, D. M„ 1984. Fractal dimension of a coral reef at ecological scales: discussion. Mar. Eco/. Prog. Ser., 14: 293-294. -MATTHEWS, J. B. L„ A. L. ALDRED6E. R. L. HAEDRICH. J. PALOHEIMO, L. SALDANHA. G. D. SHARP 6 E. URSIN. 19B4. Carnivory. In: M. J. R. Fasham (ed.). Flows of Energy and Materials in Marine Ecosystems: Theory and Practice. HA TO Conference Series IV: Marine Sciences 13. Plenum Press, New York : 695-706. -MCKELVIE, D. S„ 1953. The discreteness of pelagic faunal regions. Mar. Bio!., Bd{2): 125-133. -MORSE, D. R.. J. H. LAWTON. M. M. DODSON 8, M. H. WILLIAMSON. 1965. Fractal dimension of vegetation and the distribution of arthropod body lengths. Nature, 3/4: 731-733. -PETERS, R. H.. 1983. The Ecological Implications of Body Size. Carrtbrldge Univ. -112- TOWARD A STUDY OF THE BI06E0GRAPHY OF PELAGIC CTENOPHORES G.R.HARBiSON Woods Hole Oceonographic Institution, U.S.A. INTRODUCTION the DSRV JOHNSON-SEA-LINK II, to collect mesopelogfc organisms, it soon became apparent Ctenopflores are one of the most difficult of ali that the epipelagic ctenophora fauna is extremely groups of pelagic animals to study. They are sparse, when compared with the midwater fauna represented only sporadically in net collections, (see Youngbluth, 1984a for a description of the so that the majority of the large oceanographic collecting devices). We collected six species by expedition reports do not even mention them, and SCUBA diving - Ocyropsis maculata those few reports that do deal with them (Chun, immaculata Harbison & Miller (1986); 1898; 1900; Moser, 1903; 1909; Mortensen, furham phaea vexilligera Gegenbaur ,1856; 1912; 1913) report the collection of only a Bolinopsis vitrea Agassiz, I860; Hormi handful of specimens. One gains the Impression, phora sp.; Cestum veneris; mû Beroe sp. At based on the results of these "quantitative" depths of about 600m, however, we collected et sampling studies, that ctenophores represent an leest 22 different species of ctenophores, of which insignificant fraction of the fauna of the open sea. only five have been previously described. (Figs Over the past decade, however, collections made le, 2). Of these five species, only two, Batho by SCUBA divers have revealed that only a small cyroe fosteri Madin & Harbison, 1978a and fraction of the epipelagic species can be collected Bathyctena chuni (Moser, 1909) had been with nets (Harbison et al., 1978). The reason for described es deep-sea species. Two of the others, the discrepancy between the results of net Kiyohimea aurita Komai & Tokioka, 1940 collections and the results of SCUBA collections is and Thalassocalyce inconstans Madin & obvious - most species of ctenophores are simply Harbison, 1978b, are occasionally advected into too delicate to be collected with convential surface waters. The lest species, Cu ram phaea plankton sampling techniques. Of those few species vexilligera, appears to be a truly epipelagic that can be collected with nets, only a small animal, since we collected only a single specimen fraction can be preserved in recognizable with the submersible, while numerous specimens condition. Therefore, most of the species were collected with SCUBA. Since over 75* of the commonly collected by SCUBA divers are never species of ctenophores that we collected with the seen by most zooplankton ecologists. Six common submersible were undescribed, and there were epipelagic species are shown in figure 1. Many three times as many species at 600m than in the more could be shown, of course, such as the most upper 30m, the most reasonable conclusion that ubiquitous of ali of the epipelagic ctenophores, can be drawn is that the vast majority of Cestum veneris Lesueur, 1813 (Harbison et ctenophores live in the deep sea, and that they are al., 1978). It is obvious that the towed net is not undescribed. the technique of choice in studying the In a recent paper (Harbison, 1985), I biogeography of epipelagic ctenophores. suggested that ctenophores evolved in the open ocean , since ali but one specialized order are pelagic, and ctenophores are found in their DISTRIBUTION PATTERNS greatest diversity in the open sea. I would like to modify this speculation even farther, and suggest On a recent cruise (October to November 1984) that it appears likely that most of the evolution in the Bahamss, where we used the submersible, within the group has taken place in the deep ocean. -113- Ctenophores appear to be extremely well-adapted biotic factors in determining distribution to live there. Their large food-collecting patterns. For example, in terrestrial biogeo apparatuses, their ability to "degrow" when graphy, the importance of plant hosts in starved, and their delicacy strongly suggest that determining the distribution of insects Is they have evolved in en environment free from well-known, yet in pelagic biogeography only a hard surfaces, turbulence, mechanical stresses, few analogous examples can be cited. I think that and low in food. Almost ali species of ctenophores this does not imply that biotic factors are of little are strongly bioluminescent, a character shared consequence in the pelagic environment, but with many other mesopelagic groups. If merely reflects our present Ignorance. Figure If ctenophores did indeed evolve in the deep ocean, shows a pelagic relationship analogous to that then we are faced with a paradoxical situation thai between insects and plants. The hyperiid reveals how little we really know about life in amphipod, Glossocephalus m Une-edwards, this region of the ocean - this group of pre Bovallia, 1887, is a highly specific parasite on dominately midwater animals is known almost species of the ctenophore, Bolinopsis. Many entirely from collections made close to shore or in other hyperiid amphipods are aiso found in the epipelagic! association with large gelatinous organisms, and I did not expect to be confronted with such a often these associations are obligate (Harbison et greet number of undescribed ctenophores, and al., 1977). Since biological oceanographers were P.R.Pugh ( Institute of Oceanographic Sciences), unaware of these relationships (see Shulen- who studied the siphonophores we collected with berger, 1979 ssan example), they attempted to the submersible, had results similar to mine. He correlate the distribution patterns of hyperiid found that of the thirty species of siphonophores amphipods only with water masses or other we collected, fifteen are probably undescribed. chemical-physical parameters, rather than with Most of these undescribed species were physo- the presence of their gelatinous hosts (see Laval, nects, and one of them was over ten meters longi 1980 for a discussion of this). That such a great number of previously unknown large animals could be collected in only three weeks of diving with a submersible in a small CONCLUSIONS area in the Bahamas indicates, I think, that the study of these diverse, and potentially important It is becoming more and more apparent, as we groups of mesopelagic organisms Is only learn more about the behaviour and physiology of beginning. oceanic organisms, that very few animals are In terrestrial biogeography, it is well-known planktonic in the classical sense (that is, simply that the distribution of many organisms is passive drifters), and it is aiso becoming dependent on both physical and biotic factors. apparent that biotic factors are probably as However, in pelagic biogeography, most workers Important In determining distribution patterns of concentrate on the physical factors, giving only pelagic organisms as they are in determining the slight attention to the potential importance of distribution patterns of terrestrial organisms. Flg.1 Widely distributed epipelagic ctenophores, rarely if ever reported from net sampling studies, (a) The lobata, Leucothea multicornis (Quoy & Gaimard, 1824), photographed in situ in the western North Atlantic (0.5x). (b) Haeckelia r^/\?(Gegenbauer etal., 1853), asmall cydippe whose tentacles lack tantilla ( 1 lx), (c) The tiny blue cydippe, Tinerfe cyanea^SKm, 1889), was described from the Canaries, but this specimen was collected in the Corai Soa off Australia (16x). (d) The cydippe, Callianira bialata Chiaja, 1848, Is usually collected by SCUBA divers at night, and thus may be a vertical migrator ( 1.2x). (e) the lobate, Eurhamphaea vexilligera, is common in oligotropha regions of the tropical and subtropical Atlantic and Pacific. Photographed in situ in the Corai Sea (0.5x). (f) The lobate, Bolinopsis vitrea, is often found near coral reefs In both the Atlantic and Pacific. An hyperiid amphipod, Glossocephalus milne-edwardsi, can be seen on the oral lobe of this animal ( 0.8x). -iM- text to this figure see previous pege -115- Fig. 2 Four mesopelagic ctenophores, ali collected in the fall of 1984 in the Bahamas with a submersible, (a) The lobate, Bathocyroe fosteri, has been collected below 400m. in both the Atlantic and Pacific, and may be the most abundant of ali presently known ctenophores (1.5x). (b) The cydippe, Bathyctena chuni, was previously known from the Indian Ocean and eastern Atlantic (4.5x). (c) Thalassocalyce ineons tans was thought to be a rare epipelagic species, but submersible collections have revealed that it is common at depths below 400m. ( lx), (d) The lobate, Kiyohimea aurita, Is often found at mesopelagic depths ( 0.4x). See Youngbluth ( 1984b) for other submersible records from the Bahamas. Progress in pelagic biogeography will only come must be made to collect organisms such es through an improved understanding of ali the ctenophores, and to concentrate more on the factors responsible for the distribution and observation of midwater organisms in the field. At abundance of pelagic organisms. Increased efforts present, very few submersibles are available that -116- are adequate for the stud/ or collection of animals -CHUN, C., 1898. Die Ctenophoren der Plankton- in midwater. Elucidation cf the distribution Expedition. Ergebn. Planklon-Exped., 2 (K.a.) : patterns of large gelatinous organisms and of the 32pp., 3 pis. animals that depend on them for some part of their -CHUN, C., 1900. A us den Tiefen des We/t- life histories will only be achieved by improving meeres. Gustav Fisher. Jena : 509. our ability Io stud/ them in situ. We need to -GEGENBAUR, C. 1856. Studiën liber Organisation und Syslematik der Ctenophoren. Arch. Nalurgesch., develop techniques to quantify these "uncollect 22 : 163-205. able" organisms, and we need to be able to spend -GE6ENBAUR, C., A. KÖLLIKER & H. MÜLLER. 1853. more time in the field. Bericht liber einiae im Herbste 1852 in Messina The development of an undersea research vessel, angestellle vergteichend-anatomische Unlersuchungen. large enough to carry submersibles and support a Z. wiss. Zoo!., 4: 299-370. scientific team of about ten people, would greatly -HARBISON, G. R., 1982. The structure of planktonic accelerate progress (Harbison, 1982). With such communities. In: P. G. Brewer (ed.), Oceano a research vessel, we could spend extended periods graphy. The present and future. Springer at depth, comparing visual counts with sub Verlag, New York : 17-33. mersible and net collections. We could aiso -HARBISON. G. R.. 1985. On the classification and develop techniques for the stud/ of midwater evolution of the Ctenophora. In: S. C. Morris. J. D. George, R. Gibson, & H. M. Platt (eds). The Origins animals similar to those used by terrestrial and Relationships of Lower Invertebrates. ecologists and biogeographers. Until we are able to Clarendon Press, Oxford : 78-100 do this, pelagic biogeography will continue to lag -HARBISON. G. R„ D. C. BIGGS & L. P. MADIN. 1977. far behind terrestrial and nearshore bio The associations of Amphipoda Hyperiidea wiLh geography. gelatinous zooplankton - II. Associations with Cnidaria, Ctenophora and Radiolaria. Deep-Sea Res., 24 \ 465-468. ACKNOWLEDGMENTS -HARBISON. G. R . L. P. MADIN & N. R. SWANBERG, 1976. On the natural history and distribution of Figures la, Id, and 2a, c by R. W. Gilmer. Figure oceanic ctenophores. Deep-Sea Res., 25 : 233 la by J. Carlton. Figure If by M. Jones. Research 256. supported by National Science Foundation Grant -HARBISON. 6. R. & R. L. MILLER. 1986. Not ali OCE 84-00243. DSMC Contribution No. 7. ctenophores are hermaphrodites: studies on the systemalics, distribution, sexuality, and develop Contribution no. 6064 of the Woods Hole ment of two species of Ocyropsis. Har. Bio!., 90 : Oceanographic Institution. 413-424. -KOMAI, T & T. TOKIOKA. 1940. Kiyohimea aurita, n.gn., n.sp., type of a new family of lobata Cteno REFERENCES: phora. Annotnes Zool. japan., 19: 43-46. -LAVAL, P., 1980. Hyperiid amphipods as crustacean -AGASSIZ, L., 1860. Contributions to the parasitolds associated with gelatinous zooplankton. Natural History of the United States of Oceanogr. Mar. Biol. Ann. Rev., !8\ 11-56. America, J. Little, Brown & Co., Boston : 250, -LESUEUR, C. A., 1813. Mémoire sur quelques 269, 289, Fig. 93. nouvelles espèces d'animaux mollusques et radiaires -60VALLIUS, C.. 1887. Systematical list of the recueillis dans la Méditerranée, près de Nice. Bull. Amphipoda Hyperiidea. K. svenska Vetensk. Soc. phi/om. Paris, J(69) : 281-285, pi. 5. Akad. Handi. //( 16) : 1-50. -MADIN, L. P. & G. R. HARBISON, 1976a. Bathocyroe -CHIAJE, S. DELIE, 1841. Memorie suits S tori a e fosteri, gen.nov„ spnov.: a mesopelagic ctenophora Notomia degli Animait senza Vertebre, 4. Soc. observed and collected from a submersible. J. mar. Tipogr., Napoli : 115, pi. 66. bio/. Ass. U.K, 58: 559-564. -CHUN, C., 1889. Bericht liber eine nach den -MADIN, L. P. & G. R. Harbison, 1978b., Thalasso Kansrischen Inseln Im Winter 18B7-/88 ausgefiihrte calyce inconstans, new genus and species, an Reise. Sitzungsber. Akad. Wiss. Berlin, JO : enigmatic ctenophore representing a new family and 519-552. order. Bull. mar. Sei., 28 : 680-687. -117- -MORTENSEN, T., 1912. Ctenophora. Danish Ingolf- Exped. 5(2) : 95pp. -MORTENSEN, T., 1913. Ctenophora. "Michael Sars' N. Ali. Deep-Sea Exped. 1910. J: 1-9. -MOSER, F., 1903. Die Ctenophoren der Siboga- Expedilion. Siboga-Exped., 6: 1-34. -MOSER, F. 1909. Die Ctenophoren der Deutschen Siidpolar-Expedition. Sei. Rep. dl. Siidpofar- Exped., tt : 117-192. pis. 20-22. -QUOY, J. R. C. 8. J. P. GAIMARD. 1824. Zoologie, 2me partie. In: L. de Freycinet (ed.). Voyage autour du monde, fait par ordre du Roi, sur tes corvettes de S. M. dUranie et ia Physi cienne, pendant les années 1617, 1818, 1619 et 1820. Pillet Aine. Paris : 409-461 -SHULENBERGER, E., 1979. Distributional pattern and niche separation among North Pacific hyperiid amphipods. Deep-Sea Res., 26 A : 293-315. -YOUNGBLUTHI, M. J.. 1984a. Manned submersibles and sophisticated instrumentation: tools Tor oceanographic research. Proc. SUBTECH '83 Sympos., Soc. Underwater Tech., London : 335-344. -YOUNGBLUTHI, M. J., 1984b. Water-column ecology: in-situ observations oT marine zooplankton Trom a manned submersible. In: N. D. Fleming (ed.), Divers, Submersibles and Marine Science. Occ. Papers, Memorial Univ. Newfoundland, 9: 45-57. -118- PROBLEMS IN OPEN-OCEAN PHYTOPLANKTON BIOGEOGRAPHY GRETHE RYTTER HASLE Department of Biology, Marine Botany, University of Oslo Norway. INTRODUCTION oceanic distribution were shown to be particularly efficient in utilizing the small The phytoplankton consists of single-celled nitrogen concentrations of the oceanic waters primary producers mostly belonging to the (Eppley et al., 1969), and furthermore to have smallest size-fraction of the marine plankton generally lower requirements for zinc and iron (0.2 - 2000pm). Asexual, vegetative repro than species living in coastal waters with much duction predominates in ali taxonomic groups, and higher concentrations of these micro-nutrients the reproduction rate is high, 0.2 - 2 divisions (Brand et al., 1983). per day or more. These characteristics place the Study' of phytoplankton collected in the open phytoplankton in a unique position compared to waters of the Norwegian Sea, the Subantarctic and other inhabitants of the open ocean. The small size the Pacific Ocean by water bottles, preserved in qualifies the phytoplankton as passive drifters in neutralized formaldehyde and examined in the a V8st environment although 8s primary inverted microscope (Halldal, 1953; H8sle, producers, restricted to the euphotic zone. The 1969; Fryxell et al., 1979) has indicated further predominance of vegetative reproduction and characteristics of oceanic assemblages: firstly probably aiso the short reproduction time enable high cell numbers of small unidentified flagel the species not only to survive but aiso to lates, secondly a coccoiithophorid flora rich in reproduce outside their "range bases" es defined species and often numerically predominant, and by Semina (1979). The overwhelming dominance finally a dinof logei late flora rich in species but of the smaller individuals of the nanoplanktonic not particularly abundant. Moreover, recent diatom Nitzschia pseudonana in the open research has shown that the picoplankton (0.2 - waters of the Norwegian Sea and the Subantarctic 2pm), including blue-green algae, forms a illustrates the ability to survive by vegetative significant component of the open-ocean formation with a gradual diminution of the ceti ecosystem ( Platt et al., 1983). size; an ability which may be responsible for the The most abundant coccolithophorid in the global distribution of this species (Hasle, 1976). investigation from the central Pacific by Fryxell Although the characteristics mentioned probably et al. (1979) was Emiliania huxleyii influence the latitudinal range of phytoplankton Fryxell et al., recorded under the synonym species, they may have consequences for the Oephyrocapsa hux/eyi). Oceanic clones of this longitudinal distribution as well, i.e. cosstal species were used by Eppley et al. ( 1969) as species may drift into oceanic waters and continue representative of oceanic plankton to test to divide and vice versa. physiological and ecological attributes with the result mentioned above. However, f. hux/eyi occurs regularly in mass concentrations in CHARACTERIZATION OF OCEANIC ASSEMBLAGES Norwegian fjords during summer. The diatoms Nitzschia closterium and N. bicapitata and By the successful culturing of planktonic algae the dinoflagellate Oxytoxum variabile aiso isolated from the open ocean physiological and belonged to the ten most abundant taxa in the ecological attributes of the oceanic phytoplankton investigation by Fryxell et al., (1979); the have now been investigated. Algae with primarily former Is most probably an ubiquist while the -119- other two appear to be true oceanic species. 60*N whereas most of the remeining species were Another, extensively studied, oceanic species is recorded only south of 40*N. The species with the Thalassiosira oceanica , a diatom distinct widest latitudinal distribution were abundant in from the allied neritic Thalassiosira pseudo coastal waters and scarce, if recorded at ali, in the nana by ecological and physiological properties open ocean (e.g. C. furca ). The tropical species, as well es morphological characters ( Brand et al., on the other hand, were abundant in the open ocean 1983; Hasle, 1983), but, in the past regarded 8s and absent from the coastal stations (e.g. belonging to T.pseudonana 8S a suggested C.euarcuatum). Ceratium arcticum is one oceanic "race". of the few species of the genus characteristic of cold waters. As recorded by Graham & Bronikovsky ( 1944), it appears to be oceanic. BIOGEOGRAPHY OF THE OPEN OCEAN The diatoms Nitzschia bicapitata, Roperia tesselata mû Nitzschia americana occcur in The classification of the planktonic algae as temperate and tropical zones, N. bicap Hata neritic (including inshore and coastal), oceanic being recorded betweeen 66*N and 62*S, and panthalassic (present in neritic and oceanic R. tesselata between 66*N and 57*S, and waters) necessarily depends on the extent of the Namericana between 54*N and 44*S (Hasle, information available on the frequency of 1976). Nitzschia americana is a coastal occurrence in particular areas. It is aiso very species whereas the two others have not been much dependent on accurate identifications of taxa recorded inshore (e.g. in Norwegian fjords) and and on the personal opinions of planktologists. For may well be regarded as oceanic species often instance, many of the species classified as oceanic drifted into coastal waters, R. tesselata more so by Gran (1912) occur regularly in theOslofjord than N.bicapitata. The diatoms Thalassiosira and are thus unacceptable to the present author 8s poroseriata mû Nitzschia ( Fragilariopsis) "oceanic". kerguelensis may aiso be classified as oceanic, However, a review of more modern pertinent though cold water, species. The former hss been literature tends to add to the confusion rather than recorded between 80*N and 49*N in the North to reveal a possible pattern differentiating Atlantic Ocean and between ca. 76*S and 40*S in between coastal and oceanic species. For instance, the Southern Ocean and fairly close to the coasts of Umbellosphaera irregularis shows the more South America. Nitschia kerguelensis is common coccolithophorid distribution, being widely distributed in the Subantarctic and partly better represented in the open ocean than in aiso in the Antarctic Zone and in addition has been coastal areas and restricted by temperature found "to be scarce but nearly always present" boundaries (McIntyre & Bé, 1967), while the from 40*S to 30*N in the Atlantic Ocean (Van der few coccolithophorids present in colder waters of Spœl et al., 1973:540). the open ocean occur inshore as well (e.g. Emiliania hux/eyi, Calciopappus cauda tum. Moreover, Hallegraeff (1984) in an DISCUSSION investigation of 42 coccolithophorid species in Australian waters, recorded three species from This paper was started with the intention to give a oceanic and three from cosstal stations while the characterization of the open-ocean phytoplankton rest were present in both habitats. in order to reveal possible unique features. To do Ceratium is an autotrophic, widely distributed so, it seemed necessary to use species which in dinoflagellate genus with the highest species their distribution could be classified as oceanic diversity in the warmer seas. A stud/ of 58 and to compare them with taxonomically related species recorded from the Pacific and the North coastal and inshore species. The stud/ showed, Atlantic Oceans revealed a predominance of oceanic however, that the number of exclusively oceanic and panthalassic species (Graham & Bronikovsky, species present in the open ocean is surprisingly 1944). Seven species were recorded north of low compared to the number of panthalassic lOOW 80 oE 20 120 -121- 160 E 180 100 W 80 -t---- Fig. 2 The distribution of the panthalassic, cosmopolitan (?) dinof logei late Ceratium furcata 1), the oceanic, tropical dinoflagellate Ceratium euarcuatum (2), and the oceanic, cold-water dinoflagellate Ceratium arcticum (3). phytoplankton species. In other words, a species would be expected to be more widely panthalassic species may have the properties distributed than would the species present in the necessary for life in the open ocean. coastal zones. The open ocean, with no land barriers and the The coccolithophorid Emiliania hux/eyi and comparatively stable chemical and physical probably aiso Calciopappus caudatus may parameters, offers the ideal possibility for wide serve 8s examples of phytoplankton species distribution ranges of the mainly passively present in the open ocean tolerant enough to drifting phytoplankton species. Moreover, to be survive in coastal waters and in various panthalassic a species hss to be tolerant of biogeographical zones, thus being panthalassic and environmental fluctuations and could therefore in cosmopolitan although ecaudatus has so far general be expected to have a wider biogeo- been recorded only at lower latitudes of the graphical range latitudinally than an oceanic southern hemisphere (Fig. I)(McIntyre & Bé, species. Inside the oceanic biogeographic zones, 1967: Fig. 8). The dinoflagellate Ceratium however, the oceanic es well as the panthalassic furca (Fig. 2) and the diatom Nitzschia Fig. I The distribution of the oceanic, tropical-subtropical coccolithophorid Umbellosphaera irregularis( I ) and the panthalassic, cosmopolitan ( ?) coccolithophorid Calciopappus caudatus( 2). -122- pseudonana (tissle, 1976: Fig. 37) have a of the open-ocean phytoplankton biogeography are distribution pattern similar to that of the two discernible. This may be true: the open ocean coccolithophorids although C. furca is probably phytoplankton distributions may be much more more abundant in the open ocean and complex than those of the coastal waters. Another N.pseudonana may well be classified es oceanic. reason for the lack of more definitive results is a The records of the coccolithophorid Umbello lack of relevant data. It is therefore desirable that sphaera irregularis (Fig. 1), the dino a greater interest in this underdeveloped field of flagellate Ceratium euarcuatum (Fig. 2) and biogeography can be stimulated in the near future. the diatoms Nitzschia bicapitata and Roperia tesselata (Fig. 3) signify an oceanic distribution pattern. But, whereas the REFERENCES coccolithophorid and the Ceratium species are restricted to the tropical-subtropical zone 83 is -BRAND, L. E.. W. G. SUNDA & R. R. L. GUILLARD, usual for these groups, the two diatoms have such 1963. Limitation of marine phytoplankton repro 8 wide latitudinal distribution that it may be ductive rates by zinc, manganese, and iron. Limnoi. questioned whether the/ are tropical or Oceanogr., 28 (6) : 1182-1198. -EPPLEY, R. W„ J. N. ROGERS 8, J. J. MCCARTHY. cosmopolitan. Ceratium arcticum snd the 1969. Half-saturation constants for uptake of nitrate diatoms Thalassiosira poroseriata and and ammonium by marine phytoplankton. Limnof. Nitzschia kerguelensis es cold-water oceanic Oceanogr., M{6) : 912-920. species exhibit three different biogeographic -FRYXELL, 6. A., S. TAGUCHI & S. Z. EI-SAYED, 1979. patterns. Ceratium arcticum is restricted to Vertical distribution of diverse phytoplankton the northern hemisphere (Fig. 2 which includes communities in the central Pacific, In: J. L. Bischoff var. longipes, see Graham & Bronikovsky, 8i D. Z. Piper (eds). Narine geology and 1944). Thalassiosira poroseriata h8s been oceanography of the Pacific manganese recorded from both hemispheres but not from the nodule province. Plenum Puhi. Corp. : 203-239. tropical- subtropical zone (Fig. 4). Nitzschia -GAARDER, K. R., 1971. Comments on the distribution kerguelensis has its main distribution area in of coccolithophorids in the oceans. In: B. M. Funnel & the Southern Ocean, and its presence es far as W. R. Riedel (eds). The Nicropa/eontology of north 83 30‘N illustrates the ability of an Oceans. Cambridge Univ. Press : 97-103. -GRAHAM. H. W. & N. BRONIKOVSKY. 1944. The oceanic/panthalassic species to survive outside genus Ceratium in the Pacific and North Atlantic the basis of its species range (Fig. 4). Finally, the Oceans. Scient. Ros. Cruise VII CARNES 1C distribution of the three tropical-subtropical or 1928-1929, Biology V. Carnegie Inst. Wash. Puhi. cosmopolitan diatoms illustrates the more limited 565 :209 pp. range of a coastal than of oceanic/panthalassic -GRAN, H. H„ 1912. Bet pelagiske planleliv. In: J. species (Fig. 3). Murray & J. Hjort (eds). Atlanterhavet. H.Aschehoug & Co. W. Nygaard : 252-321. -HALLDAL, P., 1953. Phytoplankton investigations CONCLUDING REMARKS from Weathership M in the Norwegian Sea, 1948-49. Hva/rid. Skr., J8: 1-91. These examples demonstrate a highly complex -HALLEGRAEFF, 6. M„ 1984. Coccolithophorids mosaic of biogeographical patterns, and a not very (calcareous nanoplankton ) from Australian waters. Bol. Mar., 27: 229-247. distinct trend for species present In the open -HASLE, 6. R.. 1969. An analysis of the phytoplankton ocean to have wider latitudinal ranges than coastal of the Pacific Southern Ocean. Hvalrêd. Skr., 52: species. Except for this, no really unique features Fig. 3 The distribution of the oceanic, tropical-subtropical or cosmopolitan diatoms Nitzschia bicapitata (1) and Roperia tesselata (3), and the coastal, tropical-subtropical or cosmopolitan diatom Nitzschia americana^?). lOOW 80 80 loo 120 140 160 F 180 160 140 120 100 80 123- 3 2 -1 tOOW 80 60 40 20 _ PE » 40___ 60 80 IOP 120 140 160 E180 160 140 120 100 80 -UZI- -125- 1-168. -HASLE, 6. R., 1976. The biogeography of some marine planktonic diatoms. Deep-Sea Res., 23 . 319-338. -HASLE, 6. R., 1983. The marine, planktonic diatoms Thalassiosira oceanica sp.nov. and ^partheneia. J.Phycol., 19\ 220-229. -MCINTYRE, A. & A. W. H. BÉ. 1967. Modern Coccolithophoridae of the Atlantic Ocean. - I. Deep- Sea Res.. 561-597. -OKADA, H. & A. MCINTYRE, 1979. Seasonal distribution of modern coccolilhophores in the western North Atlantic Ocean. tlar.Bfo!., 54 : 319-328. -PLATT, T., S. D. V. RAO & B. IRWIN. 1983. Photosynthesis of picopiankton in the oligotrophic ocean. Nature, 30/: 702-704. -SCHEI, B.. 1975. Coccolithophorid distribution and ecology in coastal waters of North Norway. Norw. J.Bot., 22'. 217-225. Fig. 4 The distribution of the oceanic, cold-water diatoms Thalassiosira poroseriata (1) and Nitzschia kerguelensis(2). -126- PATCHES, NICHES, AND OCEANIC BIOGEOGRAPHY LOREN R. HAURY Scripps Institution of Oceanography, U.S.A. INTRODUCTION boundaries (swarms) are rare. Figure 1 does not present details of community After early emphasis on taxonomy and ocean-wide aspects of such distributions; recent work, biogeography, the interests of most plankton ecologists turned towards sampling smaller and smaller spatial dimensions until today much work deals with the micro-scale (centimeters to meters). This focus on small scales has evolved, 1 loo - in part, in an effort to understand such things as competition, resource utilization, and the 1500 H 1000 - "paradox of the plankton". As a result, the study of , 500 - the spatial limits and temporal variations of plankton distributions has been neglected, even 4 1000 - though these features are not well understood. The recent research, however, is of biogeographic value in that it has given us a reasonably clear picture of distributional variability (i.e. patchiness) of many species over scales from meters to 1000's of kilometers. This information can provfde a basis for ideas about the possible Fig. 1 Horizontal distribution of various mechanics controlling species limits and the zooplankton species 8t scales ranging from one design of field sampling needed to test hypothesis meter to 100 kilometers plotted to emphasize the arising from these ideas. similarity between profiles regardless of scale of sampling and the apparent lack of "holes" (zeroes) in distributions. No adequate data were HORIZONTAL DISTRIBUTIONS found io illustrate the 10m scale; the 1000km scale can be represented by the data of One of the features of patchiness that is evident Barraclough et al. (1969) for layers of Calanus from a synthesis of these studies is the cristatus but are not shown because of hierarchical nature of the variability (Haury et difficulty in plotting. Data sources and ancillary al., 1978; flackæ et al., 1985). This results in information: a) Cassie (1959), Polydora distributions at the smallest scales appearing larvae, pump samples from 50cm ; b) Haury et al. almost exactly like those measured over lOO's to (1983), Calanus finmarchicus copepodites, 1000's of kilometers. To Illustrate this point, Longhurst-Hardy Plankton recorder samples figure 1 replots onto comparable scales a few of from 15m; c) Smith et al. ( 1976), Acartia the data collected over the past 25 years. The data clausi males, pump samples from 7m; d) Csssie selection emphasizes that, for many species over ( 1960), Paracalanus parvus, pump samples most of their ranges, there are very few or no from 5m ; e) Mackas (1977), mixed species, "holes" (zeroes) in their distributions. These and pump samples from 3m passed through electronic much other data suggest that most heterogeneity in counter. A considerable number of other sources the plankton can best be described by frequency describing distributions of other species at other distribution models such as Cassiei (1963) depths using different collection techniques could varying mean hypothesis; patches with discrete have been used to illustrate the same points. -127- however, has shown that much of the patchiness is (e.g Boxshall, 1977; McGowan & Walker, 1979) multispecies in character (e.g. Haury & Wiebe, have provided evidence that species do not divide 1982), or at least made up of homogeneous fauna! the water column into a multiplicity of niches, assemblages (e.g. Star & Munin, 1981; Munin & defined in the simplest way as separation by Williams, 1983). Where a particular species depth. This lack of vertical separation can be may be absent in a transect probably depends illustrated in two ways: more in interactions of its vertical distribution I ) distributions of species reveal that many have and rarity with sampling technique (e.g. Haury et a similar characteristic pattern, i.e. note there al., 1983; Wiebe & Holland, 1968; McGowan & are only a few generalized patterns for many Fraundorf, 1966) than from any extended region species (Fig. 2); of zero abundens This continuity of distribution, 2) individual species of a group having a similar coupled with the potential for the ambits of pattern greatly overlap in their distributions individual organisms to be large enough to bring (Fig. 3). species together in the seme volume to interact, When vertical distributions are sampled with means that over a wide range of scales members of greater resolution, considerable overlap is still many species are not isolated from competitors, evident, indicating the absence of vertical niche predators, and each other. Thus their environment separation (Fig. 4). Vertical mobility, especially may be fairly predictable over their lifetimes diel vertical migrations, coupled with vertical from the standpoint of community structure. This variations in horizontal current structure, would generalization may hold for much of the open be expected to have an even more important ocean, but perhaps not for places like the integrating effect on potential species interactions California Current, which is an ecolone than the horizontal component of ambits. (McGowan, 1974; 1977). BIOGEOGRAPHIC IMPLICATIONS VERTICAL DISTRIBUTIONS The motivation for much of the recent work on The above considerations can be extended to small-scale distributions of zooplankton is the vertical distributions es well; several studies hope that by looking at distributions on spatial COHERENCE (SUfttlER) AVERAGE PERCENTAGE Of GROUP PRESENT 0 50 100560 50 100% 0 50 100% 0 50 100% 0 50 100% 0 50 100% 0 50 100% Depth bn) ------OAY ...... TWILIGHT ------NIGHT Fig 2 Example of the extensive overlap in vertical distributions of copepods of the North Pacific central gyre. A total of 70 species grouped into 7 patterns, two-thirds of them (48 spp) into only 3 patterns (From Fig. 6 of McGowan & Walker, 1979). -125- NUMBtRS/ lOOOm3 500 1000 500 1000 rr> ~~ --- 700 400 ..... 200 --- 400 CLIMAX --- 100 -- 700 ---- 100 --- 700 STA 90.60 es» — GROUP I l5of 24m«ri»s) / / GROUP !(»-( 24 members) / / ‘ 600 -* Depth(m) O_ STA 90.30 Fig. 3 Individual copepod species depth curves for the 24 species of Group 1 of figure 2. (From Fig. 19 of McGowan & Walker, 1979). scales relevant to individual organisms, patterns ms/ be seen that show species divide living space into discrete units that allow coexistence and thus explain the persistence of stable community structure. Within pattern at these scales, separation is sought in temporal partitioning of resource utilization and in specialization upon individual types of limiting resources or upon small portions of a resourch gradient (e.g., Fig. 4 High resolution (Longhurst-Hardy Plank Boxshall, 1981). By extension, it can be argued ton Recorder) sampling in the North Pacific that such specialization within habitats would central gyre and California Current showing the provide a mechanism for creation of species absence of separation by depth of morphologically distribution limits through the lack of flexibility similar species of the copepod genus Pleuro to adapt to changing (or different) conditions mamma, Station positions are: 90.30, coastal within or between habitats. Few data are available Southern California (33*25^, 117‘54'W); to test this argument, but studies of Copepoda in 90.60, offshore California Current (32*25'N, highly diverse communities (for example, in very 119‘58'W); Climax, North Pacific central gyre old, stable ecosystems like the North Pacific (28*N,155*W).( Haury, unpubl. data). Central Gyre: Hayward & McGowan, 1979; Hayward, 1980; McGowan & Walker, 1979; resource utilization. 1985) show that they have not evolved temporal As a consequence of this lack of separation or spatial specialization in their patterns of and/or specialization at the micro-and fine-scale -129- SUMMED COUNT o* O I I I I 11 _1_ I » I LEuL • -L I I I I ul J_L -Ul IJU Pleuromamma borealis SW i*8 P robusta O' P abdominalis SS O'-J P xiphias SW-GS-SS i» rJ P gracilis SS <3 cn P piseki SS c-0> gi CD o Candacia pachydactyla SW-GS g C curta SS levels, it appears that studies at this scale may be of little use to document mechanisms governing C armata SW biogegraphic limits based on niche concepts, Paracandacia stmp'ex,. SS resource partitioning, etc. The interactions P bispinosa (Coo 'e»' between species that do go on at this scale could be C bipinnata of importance in determining the outcome of the C poen, longimana mixing of water masses containing different Pjrjcinjjcis bispinea communities, but these may very well be Pirjctnjjcn^ simpte*■ F M predictable solely on the basis of physical processes and the physical/chemical composition of the resulting water mass. That physical mixing end stirring can bring diverse planktonic communities together into homogeneous biological structures is shown in figure 5. I believe the proper scale of studies to under stand biogeographic boundaries and their stability should be kilometers to 100‘s of kilometers horizontally end 10's to 100's of meters vertic ally. These studies should be conducted in two general areas: 1) within the core regions (McOowan, 1974) of the principle oceanic communities and 2) across the transition zones between those communities that are characterized by reasonably sharp physical gradients but generally indistinct community (species replacement) gradients. Fig 5 Co-occurrence of closely related copepod The concept of biogeographic core regions Is species characteristic of various water masses directly related to the idea that several within a small region of well-mixed water fundamentally different oceanic ecosystems exist. between North Atlantic Slope water and a Gulf In core regions it is probable that the long-term Stream warm core ring. Samples collected with a average character of processes (including the Longhurst-Hardy Plankton Recorder at a depth of variance and probability of extrema) provides the 35 ( +. 1 m), temperature of 20.33 (+. 0.03*C), control,' and not the small-scale temporal and and salinity of 34.37 (+. 0.01). a) Horizontal spatial features. Understanding the regulating distributions of species over about 1800m of tow; processes in core regions and how they differ b) histograms of total abundance of two groups of between oceanic ecosystems, then, is a related species. Species affinities are denoted by: prerequisite to obtaining an understanding of SW= North Atlantic Slope water; SS= Sargasso factors which mediate community gradients Sea; QS= Gulf Stream. ( Haury,unpubl. data). between core regions. Such studies should there -130- fore be of a long-term nature, concentrating on A wide size range of organisms should be variability in community structure associated sampled as well, since the potential biological with things like the meso-scale eddy field and interactions between size classes are just as inter-annual variations in the large-scale important as biological/physical interactions. It physical /chemical field. is essential to include nektonic organisms because In the transition zones between core regions and they are less dependent upon physical features and in larga ecotones like the California Current, it is are important predators upon the smaller size not at ali clear what the structure of community classes. gradients is really like. As Boltovskcy and Angel Other types of studies will be necessary, but are (both in this volume) and McGowan (1971; probably not possible on any scale approaching 1974) have pointed out, the species making up a that recommended above. Knowing distributions biogeographic unit in one place (core region) do (presence/absence or relative abundance) and not uniformity drop out across obvious physical associated environmental parameters alone will gradients. That is, many species do not react in the not lead to an understanding of mechanisms. same way to physical boundaries. Because most Coarse-and meso-scale variability In fecundity, studies of biogeographic gradients at core region growth rates, behavioral traits, potential for boundaries have been done at scales too large to genetic exhange (Bucklin, Marcus; this volume) resolve distributional changes in relation of etc., may reflect the mechanisms determining a physical features, it is not at ali clear whether ali species success in a particular environment or species distributional limits can be correlated particular environmental and biotic gradient. with front-like features or whether sharp Ali these sampling goals sre not new to community boundaries that have been observed at biological oceanography and have been used to places like fronts are the exception, not the rule, stud/ other problems. The challenge to biogeo when entire ecosystems are considered. Detailed graphers is to employ them on the large scale studies of the relationships of community necessary to bring progress to the field. I hope the structure to physical structure on the coarse- to arguments presented here help direct limited meso-scale would thus seem essential to resolve resources towards those scales which may produce processes within gradient regions. Temporal the greatest «frances in understanding. aspects may aiso be important here, especially to address questions about the variability of boundary structures. ACKNOWLEDGEMENT I am grateful to Dr J. A. McGowan and P. Walker SAMPLING IMPLICATIONS for permission to use their illustrations which form figures 2 and 3. This work wss supported by Within biogeographic core regions, it is probably the Marine Life Research Group of the Scripps at the meso-scale that the important interactions Institution of Oceanography and by Office of Naval between species and between the community Research grant NOOOi 4-80-C-0440. members themselves and physical features and processes will occur. The continuous nature of the patch structure within core regions suggests it is REFERENCES essential to sample as continuously as possible over scales ranging from several kilometers to -BARRACL0U6H, W. E„ R. J. LEBRASSEUR U 0. 0. 100’s of kilometers. In transition zones, without KENNEDY, 1969. Shallow scattering layer In the prior Information on the location or Intensity of subarctic Pacific Ocean: detection by high-frequency physical/chemical gradients, continuous sampling echo sounder. Science, 166: 611 -613. to scales of lOO's of meters would be required to -60XSHALL, 6. A., 1977. Thé depth distributions and insure adequate resolution of the structure of community organization of the planktonic cyclopolds (Crustacea: Copepoda) of the Cape Verde Islands community gradients. -131- region. J. mar. Mol. Ass. U.K., 57: 543-568. relationship between size of net used and estimates of -BOXSHALL, 6. A.. 1981. Community structure and zooplankton diversity. Limnot. Oceanogr., it : resource partlonlng-lhe plankton. In : P. L. Forey (ed.) 456-469. The Evolving Biosphère. Cambridge Univ.Prerj, -MC60WAN. J. A. & P.W. WALKER, 1979. Structure Cambridge : 143-156. in the copepod community of the North Pacific Central -CASSIE, R. M., 1959. Micro-distribution of plankton. Gyre. Eco!. Monogr., 49: 195-226. New Zealand J. Sei., 2: 398-409. -MCGOWAN. J. A. & P. W. WALKER, 1985. Dominance -CASSIE, R. M., 1960. Factors influencing the and diversity maintenance in an oceanic ecosystem. distribution pattern of plankton in the mixing zone Eco/, tionogr., 55 : 103-118. between oceanic and tiarbour waters. New Zealand -MULLIM, M. M. & W. T. WILLIAMS. 1983. J. Sei., J: 26-50. Spatial-temporal scales of zooplanktonic assemblages -CASSIE, R. M., 1963. Microdistribution of plankton. in three areas of the North Pacific-a further analysis. Oceanogr. mar. Sio!. Ann. Rev., 1: 223-252. Deep-Sea Ros.. 30: 569-574. -MAURY, L. R„ J. A. MCGOWAN & P. H. WIEBE, 1978. -SMITH. L. R„ C. B. MILLER & R. L. HOLTON. 1976. Patterns and processes in the time-space scales of Small-scale horizontal distribution of coastal plankton distributions. In : J. H. Steele ( ed.), Spatial copepods. J. exp. mar. Bioi. Eco/., 23 : Pattern in Plankton Communities. Plenum, New 241-253. York : 277-327. -STAR, J. L. & M. M. MULLIN, 1981. Zooplanktonic -MAURY, L. R. & P. H. WIEBE. 1982. Fine-scale assemblages in three areas of the North Pacific as multi-species aggregations of oceanic plankton. revealed by continuous horizontal transects. Deep -Soa Pes., 29: 915-921. Deep-Sea Res., 28: 1303-1322. -MAURY, L. R., P. H. WIEBE, M. H. QRR & M. 6. -WIEBE. P. H. & W. R. HOLLAND, 1968. Plankton BRISCOE, 1983. Tidally generated high-frequency patchiness: effects on repeated net tows. Limnot. internal wave packets and their effects on plankton in Oceanogr., 13: 315-321. Massachusetts Bay. J. mar. Ros., 4! : 65-112. -HAYWARD, T. L, 1980. Spatial and temporal feeding patterns of copepods from the North Pacific Central 6yre. Mar. Bioi., 58: 295-309. -HAYWARD, T.L. & J.A. MCGOWAN. 1979. Pattern and structure in an oceanic zooplankton community. Am. Zoo!., !9: 1045-1055. -MACKAS, D. L.. 1977. Horizontal spatial variability and covariability of marine phytoplankton and zooplankton. Ph. D. Thesis, Dalhousia IJniv., Halifax, Canada. -MACKAS, D. L, K. L. DENMAN & M. R. ABBOTT, t985. Plankton patchiness: biology in the physical vernacular. Bull. mar. Sei., 37: 652-674. -MC60WAN, J. A., 1971. Oceanic biogeography of the Pacific. In : B. M. Funnell & W. R. Riedel (eds). The Hicrops/eentology of Oceans. Cambridge Univ. Press, Cambridge : 3-74. -MC60WAN, J. A„ 1974. The nature of oceanic ecosystems. In : C. B. Miller (ed.) The Biology of the Oceanic Pacific, Oregon State Univ. Press, Corvallis, Oregon : 9-28. -MC60WAN, J. A., 1977. What regulates pelagic community structure In the Pacific? In : N. R. Anderson & B. J. Zahuranec (eds), Ocean Sound Scattering Prediction. Plenum, New York : 423-444. -MC60WAN, J. A. & V. J. FRAUNOORF, 1966. The -133- VARIABILITY IN PRODUCTION AND THE ROLE OF DISTURBANCE IN TWO PELAGIC ECOSYSTEMS. THOMAS L. HAYWARD Scripps institution of Oceanography USA. INTRODUCTION an individual; sueli as the generation time (Hutchinson, 1961), the time from hatching to Environmental heterogeneity and the resulting first feeding (Lasker, 1975), or the time from variability in primary production and in the last feeding to starvation (Dagg, 1977). The standing stocks of phytoplankton and zooplankton important spatial scales reflect the ambit of an in pelagic ecosystems may have an importait individual over these critical periods (Richerson effect upon planktonic species structure and, th s et al., 1970). These scales depend upon the size indirectly, upon biogeographic patterns. « and trophic status of the taxon, and they thus intensity and scales of heterogeneity ( in the r i n differ greatly for phytoplankton, macrozoo of Pielou, 1974) and the biological response t<, it plankton and nekton. Physical scales that roughly are of particular interest here. The magnitude of correspond to the mesoscale ( tens to hundreds of patchiness in populations is an index of the kilometers) are likely to be especially important strength of the biological response of the system for mscrozooplankton and nekton because this to environmental perturbations; the scale of the scale Is of the same order as their ambit. response determines what fractions of the The intensity of environmental heterogeneity is populations are affected and what the ecological aiso important. Central to this argument is the consequences may be. Environmental hetero hypothesis that Interspecific Interactions will be geneity may affect the outcome of interspecific the major determinant of species structure when interactions (DeMott, 1983) and it may and where the environment is sufficiently stable determine the relative importance of physical and to permit this. That is, a "steady-state" set of biological processes in effecting species species proportions should be reached in a structure. The question to be dealt with here is invariant environment; although this need not be a whether biological processes (interspecific unique set and a limit cycle could be reached. The interactions) or physical processes (variations in question is whether heterogeneity in the environmental structure) ere likely to be of environment perturbs the expected "steady-state" greeter importance in affecting species structure. species proportions faster than the rete at which Interspecific Interactions are assumed to be of the actual species proportions approach "steady- relatively greater importance where the state". If thé environment varies in space or time environment is “sufficiently" stable. This may faster than the biotic system can respond, then lead to Insights Into the extent to which the range steady state with possible local extinctions will of a species end its patterns of abundance (and not bé reached (Caswell, 1978). The potentially thus biogeographic patterns) are influenced by great importance of interspecific interactions in interspecific interactions. planktonic ecosystems Is supported by observ Perturbations on certain spatial and temporal ations in lakes that competition and predation can scales can a-priori be expected to have a dramatically alter species proportions and even disproportionate affect upon community result in local extinctions over the course of a structure. The most significant scales in thé single season (Sprules, 1972). regulation of species structure are set by the In this paper I compare patterns of production biological characteristics of a species rather than and standing stocks In the central North Pacific by physical processes. The Important temporal and California Current ecosystems In order to ask scales are related to critical periods in the life of whether these environments are sufficiently -134- stable so that interspecific interactions are likely temporal variations are seen, but they are to have a major role in determining species scarcely greater in intensity then small-scale structure. The discussion fxuses upon macro variability (Table I). zooplankton and nekton populations because the We can aiso ask if the spatial and temporal sampling scales were too large to assess the variations in these properties are in ter cor related affects of environmental heterogeneity upon and, if so, on what scales. A lack of correlation microplankton. The pelagic biogeography of the should amplify the affects of patchiness. North Pacific and the roles of advective and Chlorophyll and primary production are in-situ processes in the regulation of species intercorrelated over large spatial scales within a proportions hsve been reviewed elsewhere single cruise (Haywardi Venrick, 1982). The (McGowan, 1974; 1977). large-scale spatial patterns of chlorophyll, primary production and macrozooplankton biomass in the central North Pacific are generally METHODS similar (Hayward et al., 1983; unpubl. data). Mesoscale variations in chlorophyll and macrc- The data shown here were collected, using zooplankton biomass, however, do not appear to be standard methods, on a number of different correlated. This latter observation can not be cruises (Hayward et al., 1983, Scripps statistically tested due to the design of the Institution of Oceanography, 1985). Data from sampling scheme. the May 1981 CalCOFI cruise are considered in The interannual variations in chlorophyll, detail because a set of within-station replicate primary production, or macrozooplankton at a samples was taken. Chlorophyll, extracted in 90* single station are ali uncorrelated (Fig. 1). This acetone, was measured with a fluorometer. is surprising given the good correlation between Primary production wœ measured es 14C uptake the spatial distributions of integrated chlorophyll in half- day (local apparent noon to sunset), and primary production. However, other data simulated in-situ incubations. These data are (Bienfeng & Szyper, 1981; Bienfang et al. presented as vertica) integrations through the .1984; Ohman et al.. 1982) aiso show that, in upper 200m and the euphotic zone (surface to the area near Hawaii and in the eastern tropical ~0.5* light level) respectively. Macrozoo Pacific, the vertically integrated values of plankton was sampled with either a lm diameter chlorophyll and primary production are ring net or a 70cm bongo net. In both cases the uncorrelated on a time scale of months or on the mesh size was 0.505mm, and the nets integrated mesoscale. These observations imply that the the upper 200m of the water column. Biomsss system is at least slightly removed from trophic data are presented as wet displacement volume. steady-state on annual to interannual timescales. The same techniques were used in both ecosystems However, perturbations from steady-state are in order to allow comparison of the absolute small, at least in terms of production and standing values of these properties as well as the levels of stocks. variability. THE CALIFORNIA CURRENT The small-scale, within-station variability In OBSERVATIONS primary production and standing stocks in the California Current is similar to that in the THE CENTRAL NORTH PACIFIC central North Pacific (Table I). Variability on Variability in the given biotic properties is low meso and larger spatial scales is much greater. on ali spatial and temporal scales in the central The contrast with the central North Pacific is North Pacific (Hayward et al., 1983). greatest in the Intensity of the mesoscale Within-station variability over two or three days patchiness. Seasonal and interennual variations is typically a factor of two or three. Meso and ere aiso greater in the California Current than in large-scale spatial variations and interannual the Central North Pacific. -135- Table I Estimates of the biological variability on various spatial and temporal scales in the Central North Pacific and California Current. Within-station variability is that at a single station (< IO km) over a few days. Mesoscale is lens to hundreds of kilometers, and large scale is hundreds to thousands of kilometers. These are subjective estimates based upon an examination of the available data. Insufficient data exist to estimate the interannual variability in chlorophyll and primary production in the California Current. CENTRAL NORTH PACIFIC Chlorophyll Primary ttocrozoo- Pr ariodi on plankton Biomass Spoco Vitilia station <2 2-3 1.5-2 Moso-scolo 2 2-3 2-3 Larga-scala 2 2-3 3-4 Tima (Hoi 1 ---- 1.5 Seasonal <1.5 <1.5 <1.5 lator annual 2 3 1.5 CALIFORNIA CURRENT Spoco Within station <2 2-3 2-3 Moso-scalo 5 IO 50 Large-scale IO IO IO Tima (Hoi <2 ---- 1.5-2 Seasonal 3-4 2-3 3 lotor an nooi ? ? 5 The meso and large-scale spatial distributions fraction of the total area of the Calit>. Jia Current of chlorophyll, primary production and macro (Fig. 5; Hayward, in prep.). There Is a large area zooplankton biomass are intercorrelated within a outside the patches that csn be thought of as a single cruise, but there is considerable varia "background". This background contains most of bility with this relation, especially for macro the area of the California Current but only a small zooplankton biomass (Fig. 2). Chlorophyll and fraction of the total standing stocks. The primary production, spatially integrated over the background area has standing stocks that are often Southern California Bight, are uncorrelated on a not enriched with repect to the central North time scale of months (Fig. 3). Macrozooplankton Pacific, and this ares thus may itself be much biomass and production are correlated on this closer to a trophic steady state. time scale (Smith fcEppley, 1981). Mesoscale patchiness in the California Current is the dominant feature. The contrast between DISCUSSION patches and the area surrounding them may be a factor of 50 or more in the given properties (Fig. What effects are these patterns of variability In 4). Most of the standing stocks of phytoplankton production and standing stocks likely to have upon and macrozooplankton are eggregoted in a 3mall planktonic species structure in these ecosystems? -136- CLIMAX AREA (28°N, 155°W) CLIMAX AREA (28°N, I55°W) C'jse Vej-s io Cruise Means 'é 100- c o O2 o D ' Ê 80- Oo LO all f/i«4 >- O5 60 - Is the environment sufficiently stable, and on Pacific implies that the system is close to trophic what scales, so that interspecific interactions steady state. This aiso suggests that the expected have an Important effect upon the species "steady-state" species proportions do not vary structure? greatly. This, in turn, suggests that interspecific Heterogeneity in the relation between the interactions pier/ the dominant rote in distributions of the given properties shows that determining species proportions. The great environmental variability is greater than stability observed in the species proportions of indicated by patchiness in eny single property. trophic levels Including phytoplankton (Venrtck, Patterns in an individual property are thus 1982), mocrozooplonkton (McOowan & Walker, insufficient to fully describe the biological 1979; 1984), and nekton (Barnett, 1983) is response of these ecosystems. consistent with strong regulation of species The low overall variability In the central North structure. However, the processes which maintain -137- this stable species structure remain unclear ( McGowan & Walker, 1984). C.D Cfc 9 CO • £ a The way in which environmental variability i O affects species structure in the California Current 5 J €-90 1 * ? may be more complicated. Variability on small (within station) scales is similar to that in the S £ u W I central North Pacific., and this Is probably well £ E i r* within the range of Individual adaption of the macrozooplankton and nekton. Variability on meso NTEGRATED O^ORC^u L ( Ch -o < and larger scales is much greater than In the eo central North Pacific. Patches on these scales < 5 IOOO-» O 8I05 likely constitute different environments, and each patch could have a different expected "steady- o e state" species structure. Thus, the system œ a i¥— O Z O whole is probably far from steady-state species < O 500- d' proportions. The observed species proportions si -86I vary greatly from sample to sample (McGowan, N CCO _*••• 1974). This variability should decrease the O JP' relative importance of interspecific interactions < ( ~i r i r"i r*r~r I I loo 200 300 in regulating the overall species proportions of INTEGRATED CHLOROPHYLL mg chl-o/m2 this system. The low correlation between the spatial distributions of chlorophyll and macrozooplankton Fig. 2 Scatter plots of the spatial variability in biomass suggests that the area within patches is intergrated chlorophyll versus Integrated often far removed from trophic steady state. It is primary production and macrozooplankton bio unknown whether the species structure within mass in the California Current on cruise 8105 patches is close to steady-state. In order to assess (May 1981). Both relations are significantly the effects of meso and larger scale physical correlated at the 0.05 level. forcing processes it will be necessary to know more about the persistence of patches and the exchange rate of individuals and properties southern california bight between them. X The background in the California Current may constitute an environment which is distinct from —,L that in patches and which itself may ba closer to trophic steady state. The very low values of pr oduction and standing stocks suggest that this area has not recently been perturbed. If this is the X X Xx X case, the background In the California Current X X may be sufficiently stable so that interspecific IO 20 50 40 *>o interactions have a significant effect upon species INTEGRATED CHLOROPHYLL (rngcM O/rr.*) proportions. It Is thus aiso necessary to know more of the history of the water parcel from Fig. 3 Scatter plots showing the temporal which samples are collected. variability In Integrated chlorophyll and The low-frequency, large-scale variability In integrated primary production in the Southern the California Current is associated with physical California Bight region. Each point is a spatially events such as El Nino (Chelton et al., 1982). averaged cruise mesa There is no correlation at Changes on this very large scale tend to be the 0.05 level. spatially coherent throughout the system. -130- INTEGRATED • PRIMARY CHLOROPHYLL S4N PRODUCTION mgcé/pm2/'half day mg chl-a /m2 experiment [Until- <150 nina: IiIt.cn---- —-150-300 I------300-600 1------>600 v1'1;’ 'I» V '/\\\ - CRUISE 8105 CRUISE 8105 i?5* »?0° MACROZOOPLANKTON S1. BIOMASS ml/IOOOm -100-200 ' 200-400 >400 Fig. 4 Spatial distributions of integrated chlorophyll, integrated primary production, and mecrozooplankton biomass in the California Current on CalCOFI cruise 8015 ( May 1981). - CRUISE 8105 Variations in the abundance and distributions of of the system and external processes. A detailed taxonomic groups (Colebrook, 1977) end examination of a single place or time is unlikely individual species (Brinton, 1981) are aiso to represent the range of environmental associated with environmental variations on this conditluns that the populations are exposed to over scale. evolutionary time. Studies of In-situ structuring The species proportions in the California processes must consider the range of environ Current thus repond to both the in-situ structure mental variability in the California Current. -139- 8105 ACKNOWLEDGEMENTS Drs. Loren Haury, John McGowan, and Elizabeth Yenrick collaborated on the planning and sampling AREA at sea and engaged in many helpful discussions. I thank Dr.Richard Eppley for making the data from the South California Bight time series available to CHLOROPHYLL me.Support was provided by the Office of Naval Research and the Marine Life Research Group of the Scripps Institution of Oceanography. LOG CHiOROPHYLL (mg Chl-a/m2) REFERENCES -BARNETT, M. A.. 1983. Species structure and temporal stability of mesopelagic fish assemblages in the central gyre of the North and South Pacific Ocean. ARCA Mar. Bio)., 74: 245-256. -BIENFAN6, P. K. & J. P. SZYPER, 1901. Phyto plankton dynamics in the subtropica) Pacific Ocean off Hawaii. Deep -See Pes., 26: 981-1000. MACROZOOPLANKTON BIOMASS -6IENFANG, P. K.. J. P. SZYPER. M. Y. OKAMOTO 8, E. K. NOD A, 1984 . Temporal and spatial variability of phytoplankton in a subtropical ecosystem. Limno). Oceanogr., 29: 527-539. LOO B'OMASS (ml/IOOOml) -BRINTON, E., 1981. Euphausia distributions in the California Current during the warm winter-spring of 1977-78, in the context of the 1949-1966 time Fig. 5 (a) Summary of patchiness In the series. CalCOFI Rep., 22: 135-154. California Current on cruise 8105. The -CASWELL, H.. 1978. Predator-mediated coexist cumulative percentage of area is the fraction of ence: A nonequilibrium model. Am. Nat., ))2: the total area in the sampling grid (Fig.4) that 127-154. has chlorophyll concentrations at or below that -CHELTON, D. B.. P. A. BERNAL 8, J. A. MCGOWAN. 1962. Large-scale interannual physical and biological shown on the x axis. The cumulative chlorophyll interaction in the California Current. J. mar. Res., is the fraction of the total integrated chlorophyll 40: 1095-1125. in the grid at or below that chlorophyll -COLEBROOK, J. M., 1977 Annual fluctuations in bio concentration. If chlorophyll is evenly distributed mass of taxonomic groups of zooplankton in the the curves will overlay. The difference in the California Current. 1955-59. Fish. Bull., 75 : curves shows the intensity of patchiness. For 357-366. example, the 50* of the cumulative area with the -DA66, M.. 1977. Some effects of patchy food lowest chlorophyll concentration has only about environments on copepods. Limno/. Oceanogr., 20* of the total chlorophyll. To reach 50* of the 22: 99-107. total chlorophyll takes about 80* of the total -OEMOTT, W. R., 1983. Seasonal succession in a area. This means that the other 50* of the total natural Daphnia assemblage. Seoi, flonogr., 5J : chlorophyll Is found in the 20* of the area with 321-340. -HAYWARD, T. L. & E. L. VENRICK, 1982. Relation the highest concentrations. between surface chlorophyll, intergrated chlorophyll (b) Same es figure 5 (a) except for macrozoo and integrated primary production. Mar. Biol., 69: plankton biomass. 247-252. -HAYWARD. T. L., E. L. VENRICK & J. A. MCGOWAN, -MO- 1983. Environmental heterogeneity end plankton community structure In the central North Pacific. J. mar. Res., 4f-l\\-T2R. -HUTCHINSON, 6. E„ 1961. The paradox or the plankton. Am. Rai., 95: 137-145. -LASKER, R„ 1975. Field criteria for survival of anchovy larvae: the relation between inshore chlorophyll maximum layers and successful first feeding. Fish. Bull., 73 : 453-462. -MCGOWAN, J. A„ 1974. The nature of oceanic ecosystems. In: C. 8. Miller (ed.). The Biology of the oceanic Rac irie. Oregon State Univ. Press, Corvallis, Oregon : 9-28. -MCGOWAN, J. A., 1977. What regulates pelagic community structure in the Pacific? In : N. R. Anderson & 8. J. Zahuranec (eds.) Ocean sound scattering prediction. Plenum Press, New York: 423-444. -MCGOWAN, J. A. 8. P. W. WALKER. 1979. Structure in Ute copepod community of Ute North Pacific central gyre. Eco), tlonogr., 48: 195-226. -MC6CWAN, J. A. 8. P.W. WALKER, 1985. Dominance and diversity maintenance in an oceanic ecosystem. Eco!, tlonogr., 55: 103-118. -OHMAN, M. D.. G. C. ANDERSON & E. 0ZTUR6UT, 1982. A multivariate analysis of planktonic Inter actions in the eastern tropical North Pacific. Deep- Sea Res., 29: 1451-1469. -PIELOU, E. C., 1974. Population end community ecology: Principles and methods. Gordon and Breech, New York : 424 pp. -SCRIPPS INSTITUTION OF OCEANOGRAPHY, 1985. Physical, Chemical and Biological Data Report, CalCOFI Cruise 8105. Scrfpps Institution of Oceanography, Reference : 85-12. -SMITH. P. E. & R. W. EPPLEY, 1981. Primary production and the anchovy population in the Southern California Bight: Comparison of time series. Limnot. Oceanogr., 27: 1-17. -SPRULES, W. 6.. 1972. EfTects of size-selective predation and food competition on high altidude zoo plankton communltes. Ecology, 53 : 375-386. -VENRICK, E. L , 1982. Phytoplankton in an oligo tropha ocean: Observations and questions. Eco!, tlonogr., 52: 129-154. -mi- MODES, TEMPOS AND CAUSES OF SPECIATION IN PLANKTONIC FORAMINIFERA YVONNE HERMAN Department of Geology, Washington State University, U.S.A. INTRODUCTION PLANKTONIC FORAMINlFERAL RECORD Calcareous shells of planktonic Foraminifera Planktonic Foraminifera are unicellular marine preserved in continous sedimentary sequences on protozoans possessing calcitic tests *30mp - the sea floor in areas of rapid sedimentation, «lOOOmp in diameter. Their abundance in above the calcite compensation depth (CCD) marine sediments in depths from aproximately provide an excellent opportunity to test various 200m to >4500m and the rapid evolution of some hypotheses of plankton spéciation including species make planktonic Foraminifera important phyletic gradualism and punctuated equilibria in biostratigrnphic zonation (e.g.Herman, 1979). (Mar/r, 1963; 1970; Gouldi Eldredge, 1977). Present-day distributional patterns show that most species are extremely sensitive to water-mass properties such es temperature, CAUSES OF EVOLUTIONARY DIVERSIFICATION salinity and oxygen content, hence their usefulness as oceanographic and paleoceenographic Bursts in evolutionary radiation have been indicators (e.g.Herman, 1979 and references attributed to the development of diverse habitats therein). by continental fragmentation (Valentine & Moores, 1972), changes in land geography and In oceanic circulation, increased climatic zonation OEOLOOIC DISTRIBUTION and decreased temperatures (Valentine, 1968; Lipps, 1970) 8s well as to higher and more Rare occurrences have been noted since Middle uniform oceanic temperatures (Fischer and Jurassic, when small, globular forms, Arthur, 1977; Thunnell, 1981) more stable Globuligerina, were first recorded in marine physical conditions (Tappan and Loeblich, 1973) sediments (Caron & Homewood, 1983). Evolving and reversals in the Earth's magnetic field ggradually, planktonic Foraminifera reached their (Simpson, 1966). peak in the Late Cretaceous, whence several low The available geologic record provides evidence and high diversity cycles are recorded; today they that in planktonic Foraminifera evolutionary are represented by about 50 species (e.g. diversification occurred when temperatures were Herman, 1979). Following the terminal fluctuating over extended time Intervals, surface Cretaceous mass extinction, the morphologically water temperatures were either Increasing or simple globigerines survived giving rise to decreasing, latitudinal temperature zonation was turborotallids and globorotaliids (Cifelli, 1969), increasing or high, sea level wss changing which diversified through the Paleocene reaching gradually and when continental fragmentation was a peak by Late Paleocene (op.cit.; Table I), proceeding at a slow and even rete (e.g. Herman, approximately 57.5my ago. The 62-57my 1979; 1981 and references thereinX Fig. 1, period, was a time of fluctuating and warm deep Table I ). and surface water temperatures, with *6-7*C differences between surface and bottom water values (Fig. 1). A decline in species diversity is recorded in Early-Middle Eocene (Cifelli, 1969; Table I Causes of evolutionary diversification in planktonic Foraminifera PLANKTONIC. TIME TECTONIC EVENTS CLIMATIC EVENTS OCEANIC EVENTS FQRAMINIFERAL EVENTS GENERAL in my 0------0.9—Orogeny peak- -0.9-0 Major glacial----Arctic becomes In Ute Arctic initial— -Onset of large amplitude- interglacial cycles perenially ice covered appearance of present climatic fluctuations Cenozoic Threshold IV day assemblages 1.6- Northward shifts of------PF diversity maximum------Antarctic & Sub- antarctic watermasses Arctic PF has no analog Arctic CCD depressed, in present oceans 2.38- Arctic flooded with------2.38-0.9 Arctic------meltwater: develop- dominated by subpolar mani of low salinity SW taxa 2.4------Cenozoic Threshold Ill------2.4-0.9 Arctic Ocean------Initial major NH— NJ Initial major NH mostly oligotropha glaciation followed I glaciation by déglaciation 3.5—Uplift of Panama —6radual temp .decline------Development NH— isthmus glaciation 5------Cooling of global DOW----PF diversity increases- 5-2.4 Arctic SOW B. DOW oxygenated. CCD elevated 5.5—Isolation of- -Regression------Temporal reduction in— Mediterranean Soa PF diversity -Strong global cooling- - Major expansion of- 6-4 Expansion of Antarctic ice Antarctic ice-cap 11- -11-1 Gredual increase- in diversity cf PF 14- -14-12 Major Ant------14-11 Dissolution- arctic ice build-up Climax 17.5- 17.5-15: III d13C peak- 18- -18-0 Numerous rapid.— ■ 18-14 PF diversity------18-14 Short-term wide' largo amplitude fluc fluctuates amplitude temp, oscil tuations of saw & DOW: lations of SOW & DOW: warming trend of SOW gradual increase in & cooling trend of DOW contrast between B t S water temp.; «38 cold- warm changes in 4 my 22- -Development of Antarc tic convergence 24—Drake Passage- -24-14 Increased------24-5 Transgressions;— -24-14 6radualincrease— opens glaciation of 24-18 Minor changes in PF diversity Antarctica: intensi in SOW & DOW temps. Major change in global fication of global planktonic biogeography climatic gradients to form latitudinal belts of assemblages from tropics to poias 25- -25-22 Development of— unrestricted clrcum- Antarctic current crea ting the thermal iso lation of Antarctica; expansion of sea-ice; increased vert.& horiz. oceanic circulation 31- -31-29 Major extinctions- followed by evolutionary appearances 35- -35-18 SOW & DOW stable- regime 36.6-Greenland sépara— Antarctic glaciation—Abrupt cooling of DOW— - 36.6-24 Stable species- -36.6-23.7 Lowest------tes from Europa; Cenozoic Threshold II diversity; gradual oceanic faunal & floral Tasman Sea-way increase diversity for entire opens Cenozoic in Oligocène: Reduction of PF low diversity gradients diversity: diversity between low & high minimum: destinctive latitudes. Antarctic faunal pro vinciality develops. Regression, end of 6lobigerines dominate warm polar climate Tabl» I (continued) PLANKTONIC. TIME TECTONIC EVENTS CLIMATIC EVENTS OCEANIC EVENTS FORAMINIFERA!. EVENTS GENERAL iii my 37- -Short.conspicuous tamp------Diversity decreases------37-35; II i,3C peak- fluctuations; DOW tamp, drop; SOW incroaso; initia tion of thermohalino circu lation; rapid drop of CCD; regrossion; SH soa leo 37.5- ■ Abrupt, major DOW cooling.------SOW warming 40- -Graduol cooling------40-37 Divorsity high.------several major extinc tions followed by evolutionary appearances 44- ■ 44-40 Gradual cooling of----- 44-40 Diversity maxima— DOW. warming of SOW few major extinctions & appearances 52 -Divorsity maxima.------53- -53-36 Labrador Soa &— Flooding of Atlantic------Rapid decrease starts----- Baffin opan Ocean with Arctic water 55 —55-38 Australia moving- 55-37 DOW & SOW------nartbward gradual cooling underway: Atlantic DOW circulation; DOW & SOW cooling commences 57- -Diversity maxima- 57-53 Decline in species divorsity 60 60-59: I il3C peak- biological production maximum 62------62-57 Fluctuating warui DOW & SOW tamps. 65—Tasman Sua------65-62 Gradual------65-62 Gradual warming- Gradual evolutionary spans ; Central warming diversification oF PF Tethys narrows. S.L. drops 67—Continents reach---Cenozoic Threshold I;- Presumed changa in------It/P boundary evani;- Selective mass extinc polar position Abrupt, largo ampli- water chemistry: mass extinctien of tions tade cooling regression: abrupt taxa at the peak of large amplitude coel- their evolutionary mg dovei opmont 70 Transgression- * Ages of events are approximate Abbreviations: BOW- bottom ocean water: DOW= deep ocean water; SCW= surface ocean water; NH= northern hemisphere; SH= southern hemisphere; CCD= carbonate compensation depth; PF= planktonic formaninifera; SL= soa leve! -146- 6 0%oPDB °C 15 20 50 55 60 65 MY Fig. I. Cenozoic oxygen and carbon isotope data of benthonic and planktonic Foraminifera, South Atlantic Ocean (from Shackleton et al., 1984). Berggren, 1971) centering around 58-50my 1). The gradual E/O extinctions are much less B.P., and following a d,3C maximum, which severe than the terminal Cretaceous mass presumably indicates high surface water decimation of the calcareous microplankton biological production (Fig. 1). Another radiation (Keller, 1983). As in the Paleocene is recorded between «44 and «37 my ago, morphologically simple globigerina survive and interrupted by extinctions 40mya, 38.2mya and diversify (op.cit.). The next major radiation 37.3mya (Keller, 1983). Recent foraminifera! commenced in Miocene culminating by Middle studies indicate that with the exception of the Miocene, «I5my ago. However, 8 number of Eocene/01 igocene (E/O) boundary, these major fluctuations in foraminifera! diversity were faunal extinctions bro abrupt events being recorded between «17 and I2my B.P. By the end followed by first appearances (Keller, 1983). of Early Miocene fully-keeled globorotalids were This time interval is characterized by a gradual diverse, orbulines and hsstigerines had aiso cooling of surface and deep water (Fig. I, Table I ); evolved; the pulleniatines appear in !.?te Miocene the trend is interrupted by a warm pulse (op.cit.) From Middle Miocene on, the planktonic centering around 38 my. A sudden major cooling foraminifera! faunas are essentially modern. event of the bottom water h83 been recorded at During the last l.7my, numerous temperature about 37my B.P. (Kennett, 1978; Keller, fluctuations are recorded (Fig. 1)( Keller, 1978; 1983)( Fig. I), but the opposite trend occurs in Herman, 1979 and references therein). surface water (Fig. 1). Sharp, short-term temperature fluctuations, by approximately 7*C were measured between «37-35 my B.P. (Fig -147- MODES AND TEMPOS OF EVOLUTION change gradually completing the transformation to 0. tumida in about 0.4my, remaining essentially Several modes of spéciation have been suggested unchanged since that time. These authors have for oceanic microplankton, they include: I. demonstrated that at least in the O.merotumida Phyletic gradualism, whereby new series arise - 0. tumida lineage "punctuated gradualism" is through gradual and continuous phyletic the spéciation mode. In another investigation, transformation within the population of an entire Malmgren & Kenneti (1981) recognized a case of species. This process is believed to proceed at a phyletic gradualism, without branching in the slow and constant rate; 2. Punctuated equilibria, evolutionary lineage of Globorotalia conoidea whereby evolution is concentrated in very rapid -^O.conom lorea -> 0.puncticulata -> events, considered instantaneous in terms of G. inflata. Scott ( 1983) disputed this lineage geologic time. This second model is believed to end suggested that 0.conoidea split and one occur in genetically isolated or semi-isolated branch gave rise to 0. inflata in a relatively populations at the outer fringes of the geographic short time thus supporting the “punctuational" range of ancestral species, followed by migration model of spéciation (op.cit.) to other areas (allopatric spéciation of Mayr, Still a somewhat different ancestral-descendant 1963; 1970; see aiso Oould and Eldredge, 1977); relationship in these and related laxa is suggested and 3. Punctuated gradualism, described by by Berggren ( 1977 and references therein). To Malmgren et al. (1983). According to these further complicate matters Arnold ( 1983) used authors, evolutionary steps could take place the evolution of 0. crassaformis from its within a bioseries in one region, without ancestor 0. cibaoensis via 0.puncticulata as migration of newly evolved species (opcit, an example of "phyletic gradualism" Different Malmgren and Kenneti, 1981). Furthermore, new opinions concerning ancestor-descendant species evolve not througn lineage branching as relationships exist in me/ lineages, however, lack required by punctuated equilibria through periods of space precludes a detailed discussion of this of rapid, but not instantaneous, phyletic problem The state of taxonomic chaos is transformation of entire populations (Malmgren exemplified by Globigerina pachyderma et al., 1983). In an interesting stud/ Malmgren referred to by various other generic names and his collaborators (ibid) have analyzed the including Aristerospira, Neogloboquadrina, lineage of warm water 0 lob or talis tumida Globorotalia, Turborotalia and Globo through the last ten million years of its quadrina This species is believed by seven evolutionary history in a southern Indian Ocean pachyderma experts to have evolved either from core. This lineage is believed to be predominantly the Globorotalia opima-meyeri group, or of Indo-Pacific origin and distribution (opcit ). from Globigerina angustiumbilicata, or 0. The evolutionary sequence leads from continuosa, or a turborotalid ancestor (in Gmerotumida -> û.p/es io/um ida -> Kenneti & Srinavasan, 1980 and references 0. tumida, with no evidence of divergence in this therein). lineage (op.cit ). The material studied, from DSDP Before the challenging problems of causes, Site 214 in water depth of 1665m W8S selected modes and rates of spéciation can be addressed we because of the shallow water, well above the need to sort out questions concerning taxonomy, lysocline, consequently these dissolution resistant phylogeny, paleoceanography and paleogeography. species were very well preserved. Sampling interval was between 5x 103 yrs and 15x 103 yrs across the Miocene/Pliocene boundary (5.3iny) ACKNOWLEDGEMENTS and 2x!05 yrs in the remainder of the section. Various morphological characters were measured I would like to thank the organizers of the The results indicate thai during the Lete Miocene Conference for the invitation to attend the 1985 the O.plesiotumida populations were in stasis Symposium and Workshop held in Noord- for »5my. About 5.6my ago the test shape began to wijkerhout, the Netherlands, and Drs W. A -148 Berggren, N. de B. Hornibrook, J. C. Ingle, and J. implications of Middle Eocene Io Oligocène planklic P. Kenneti for discussions of the various foraminifera! faunas. Mar. Micropa/eont., 7 : foraminifera! lineages, and W. A Berggren for 463-486. reviewing the manuscript. “-KENNETT. J. P.. 1978. The development of planktonic biogeography in the Southern Ocean during the Cenozoic. Mar. Micropa/eont., J: 301-345. REFERENCES -KENNETT. J. P. 8, M. S. SRINIVASAN, 1980. Surface ultrastructural variation in Neogloboquadrina -ARNOLD, A. J., 1983. Phyletic evolution in the pachyderma (Ehrenberg) : Phenotypic variation and Globorotalia crassaformis (Galloway & Wissler) phylogeny in the Late Cenozoic. Cusman Fdn Spec. lineage: a preliminary report. Paleobiol., 9 : Pub/., /9: 134-162. 390-397. -LIPPS. J. H .. 1970 : Plankton evolution. Evo/.. 2d : *-BERGER, W. H., 1982. Deep sea stratigraphy: 1-22. Cenozoic climatic steps and the search for -MALMGREN. B. A. 8. J. P. KENNETT. 1981. Phyletic chemo-climatic feedback. In: G. Einsele & A. 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H„ 1983. Divergences and phyletic early plankta foraminifera. Mar. Micropa/eont.. transformations in the history of the Globorotalia 7 . 453-462. inflata lineage. Paleobiol.. 9: 422-426. -CIFELLI. R.. 1969. Radiation of the Cenozoic “-SHACKLETON, N. J.. M. A. HALL 8. A. BOERSMA. planktonic Foraminifera. Syst. Zoo/., !8 : 1984. Oxygen and carbon isotope data from leg 74 154-168. foraminifers. In: T. C. Moore 8, P.D.Rabinowilz (eds). -flSCHER, A. G. 8. M. A. ARTHUR. 1977. Secular Initial reports DSPD 7d. Washington, U.S. variations in the pelagic realm. In : H. E. Cook & P. Govern. Printing Off. : 599-6t2. Enos (eds). Deep-water carbonate environ -SIMPSON. J. F.. 1966. Evolutionary pulsations and ments. (Tulsa. Soc. Economic paleontologists and geomagnetic polarity. Seoi. Soc. America Bull., mineralogists, Spec.Publ., 25 : 19-50. 77. 197-203. -GOULD. S. J. 8. N. ELDREDGE. 1977. Punctuated -TAPPAN. H. & A. R. LOEBLICH Jr, 1973. Evolution of equilibria: Th3 tempo and mode of evolution the oceanic plankton. Earth-Science Rev., 9 : reconsidered. Paleobiol.. J : 115-151. 207-240. -HERMAN, Y., 1979. Plankton distribution in the pasi. -THUNNELL, R. C., 1981. Cenozoic paleolemperature In : S. van der Spoel 8» A. C. Pierrot-Bults (eds). changes and planktonic foraminifera! spéciation. Zoogeography and diversity of plankton. Nature. 289.670-672. Bunge scient. Puhi. Utrecht : 29-49. -VALENTINE, J. W.. 1968. Climatic regulation of -HERMAN, Y„ 1981. Causes of massive biotic species diversification and extinction. 6eof. Soc. extinctions and explosive evolutionary diversification America Bull., 79: 273-276. throughout the Phanerozoic. Seoi., 9: 104-108. -VALENTINE, J. W. 8. E. M. MOORES. 1970. -KELLER. 6.. 1978. Late Neogena biostratigraphy and Plate-tectonic regulation of faunal diversity and sea paleoceanography of DSDP site 310 central North level : A model. Nature, 228: 657-659. Pacific and correlation with the Southwest Pacific. Mar. Micropa/eont., J: 97-119. “ -KELLER. 6.. 1983. Biochronology and paleoclimatic * Publications used for compiling Fig. I and Table I. -149- ON CURRENTS OFF NORTH-WEST AFRICA AS REVEALED BY FISH LARVAE DISTRIBUTIONS HANS-CHRISTIAN JOHN T ax ano» i sc he Arbeitsgruppe der Blologischen Anstalt Helgoland F.R.G. INTRODUCTION keya, 1983a) results from these currents. In the open ocean the Canary Current probably Displar ament by currents may affect the earlv transports large numbers of Macrorhamphosus life history of fish (see e.g. John, 196'(a; scolopax (Fig. 2) and lesser numbers of Syno Nor cross & Shaw, 1984; Power, 1984; or dontidae, Mullidae and Gadinae to the south and literature cited there). west of their bathymetrically and geographically Investigations off Northwest Africa during the confined birth places (John, 1973; Andres & past twenty years provide enough knowledge to John, 1984). fulfill part of the requirements defined by John Detailed charts (e.g. Dhi, 1967) aiso show (1984a) for the assessment of larval drift for surface currents along the NW African coastal several species. area south to Cape Blanc or, during the winter, to The broed scheme of German ichthyoplankton Cepe Verde. Several examples show that near surveys off NW Africa Is shown by figure I. The surface taxa drift along the coast (John, 1984a); suberea of particular interest (the "Mauritanian e.g. off Morocco during winter nerltlc species province”; Backus et al., 1977) has been such as Belone sretoridori and Sardina thouroughly sampled ( 178 stations) from the pilchardus were confined to a zone less than 60 surface to 150m depths. Additional samples outside of the Mauritanian province, applying identical methods, prove that peculiarities encountered are not due to sampling. Details of the cruises can be found in the literature (John, 1985; Andres & John, 1984). Unpublished results for selected species from "Meteor" cruise no. 64 (January- February 1983 off Morocco and Mauritania) and cruise no. 69 (October - November 1984, open subtropical NE Atlantic) are included here. Horizontal and vertical distribution patterns for fish larvae off Mauritania were presented by John ( 1985). The term "near-surface occurrence” refers here to vertical distributions shallower than 30m, "extended vertical distribution" to species ranging from near the surface to at least 60m, and "deeper distribution" to a maximum below 60m. The existing charts of surface currents (e.g. Angel, 1979) generally show a flow towards the south-southwest for the area along Northwest Fig. I Location and seasons of plankton sampling Africa. The southward extension of range for the 1967-1984. Lines denote transects, hatched warm-temperate ichthyofauna along the coast to areas repeated sampling. W1= winter Sp= spring tropical latitudes (e.g. Maurin, 1968; Sedlets- Su= summer Au= autumn. -150- X \ X XV ■ X . • ï9 #10-99 0iî00 M scolopax/1000 Fig. 2 Occurrences of planktonic stages of Fig. 3 Occurrences of surface larvae of the family Macrorhamphosus scolopax. Shaded: known Scomberesocidae (diagonally hatched). Solid lines or bathymetrically possible (50-400m) denote limits of distribution, broken lines area spawning grounds. Interrupted: spawning grounds where family was absent. Question marks refer to 20*N-23*N represent a southward extension of areas where data are not available. spawning 1975-1983. nautical miles (n.m.) from the shore (John, shown by Hamann et al.( 1981). 1979), while oceanic Scomberesocidae reached Seasonal and Interannual changes influence the into this range (Fig. 3; see aiso John, 1979). Off species composition and abundance of ichthyo- West Sahara Scomberesox saurus was rare plankton (Sedletskeya, 1983a; John, 1973; above the slope (John, 1973), but 70n.m. from 1985). Evidence for the effect of the reversal of the shore on average 3.2 larvae/1000m2 were surface transport normal to the coast upon the caught ( "Meteor" cruise no.64). ichthyoplankton off Morocco is indirect. During Seasonal and regional changes in the direction of upwelling sordine eggs ore obundont even offshore that current component normal to the coastline of the spawning grounds, and an offshore and are known (e.g. Wooster ot al., 1976). A shift of southward drift of sardine larvae occurs the trade winds results in offshore surface flow (Sedletskeya, 1983b). Off West Sahara, two and an upwellingof cold water during late spring, examples for offshore drift in the surface layer summer and autumn of Morocco, where during the are known (John, 1984a). Absence of S.saurus winter and early spring transport at the surface above the slope aiso must be due to the same effect is either parallel to the coest or shoreward. ( the species may occur above the slope off Cape Upwelling persists throughout the year between Blanc, when water temperatures above 17*C ore 25*N and 20*N, but only during winter and found, i.e. outside of the upwelling regime- see spring off Mauritania. During summer the coastal Hartmann, 1970). surface flow off Mauritania is northward 8nd More information about the Mauritanian coastal onshore. Dete on the interannual variability are upwelling has now become available (John, described by Sedykh (1978) and Michelchen 1985). These dota allow on interpretation of the ( 1984). The effect of a reversal of surface flow literature and preliminary results from a recent off Mauritania on the distribution of larvae was cruise, even though final hydrographic data are Fig. 4 Horizontal larval distribution patterns of 3 species with extended vertical distribution during different winters. -152- notyet available. The horizontal patterns of some upwelling the deeper living larvae are carried species with extended vertical distribution (Figs. onshore by water masses feeding the upwelling 4,5) will be compared, es they represent almost (Hamann et al., 1981), while during weak up ali the mechanisms involved. Within this group, welling, shelf waters ere devoid of larvae Trachurus trachurussvvnns above the mid (Bendixen, l977)(Fig. 4 for 1983). Another shelf. Vertically, consistently more then 50JS of example has been given by John( 1985) for deep the larvae occurred in the upper 30m and neuston Bathylagus larvae. tows yielded high numbers. These larvae should be While both near-surface nerltlc (see 8S well most affected by drift of surface waters. other examples by John, 1984a; 1985) and deep Consequently, larvae occurred above the living slope or oceanic larvae reveal transport spawning places when upwelling was low (data by normal to the coast correlated with upwelling Kalinina & Sedletskeya, 1979, see Fig. 4), and intensity, no such transport became evident for closer to the spawning grounds, when, during a those larvae spawned above the shelf edge or season of intense upwelling, the surface flow was upper slope and which have a maximum reversed ( 1977 - 18'N compared with the other occurrence in the upper part of the undercurrent transects). From a multitude of distribution data (e.g. Merluccius senegalensis and soleid for the years 1963 to 1983 on Trachurus genus Microchirus ; Figs 4, 5). In the (Wiktor, 1971; Klliachenkova, 1970; Sedlets- literature additional data exist only for keya, 1975; Bendixen, 1977; Kalinina & Podo- M.senegalensis (Kalinina & Sebletskaya, sinikov 1978; Fig. 4 for 1983), the above 1979) and Soleidae, end ali these agree (Wiktor, mentioned two patterns represent the extremes of 1971; Kalinina & Podosinnikov, 1978). It is nearshore and offshore occurrences so far therefore concluded that the distributions of described - and they come from years with very larvae with known and restricted spawning areas different upwelling intensities (Sedykh, 1978). are good indicators for currents. It is further Myctophum punctatum is an oceanic to more speculated that In the Mauritanian area slope-spawning species, the larvae hsve a fairly larvae spawned at the shelf edge and upper slope even abundance from near the surface to 60m which have an intermediate vertical distribution occurring aiso below 60m. During strong suffer little removal from adult habitats. Soleidae ct o a# • s % « # ■ * : February 1983 Fig. 5 Horizontal distributions of larvae of deep-spawning solelds during three surveys. -153- Considering removal of plankton from its adequate environment, biologists have suggested recirculation models (e.g. Richert, 1975). Mesoscale gyres (<120n.m. diameter), such as proposed by e.g. Mittelstaedt ( 1974) and Shaffer ( 1976), would help to explain recirculation even of organisms with a rather short planktonic phase, like that of some of the fish larvae encountered, but no biological evidence exists. On the basis of repeated measurements of northward flow off the Mauritanian shelf, Mittelstaedt ( 1983: Figs 3, 4) proposed a gyral current which is pertly supported by Stremma ( 1984). Though this gyre has too large a scale for a recirculation of fish larvae and the actual knowledge of hydrography might equally well be interpreted by a near-shore poleward and the oceanic southward Canary Current ( Hagen ,1981; Hagen & Schemainda, 1984), it shows some Fia 6 Occurrences of larvae of the oceanic genus striking congruence with ichthyogeography. The Cyclothone. Dots: Occurrences disregarding boundaries of the Mauritanian upwelling province seasons. Open triangles: Occurrences only in agree feirly well with the extremes covered by autumn. this gyre, so that the existence of the province would easily be explained by a nearly self above the deeper slope. Some few larvae, however, contained system in the eplpelagic rone. The were caught in this "Cyclothone hole” during problem to identify larvae of the two myctophid autumn 1972. As the larvae were always among species characteristic for this province the regularly caught taxa in adjacent areas, a (L am patena pontifex and Diaphus holti) seasonal cycle in reproduction off Mauritania did not yet allow study of this question, but Krefft seems less likely. Contrary to Scomberesocidae, (pers. comm.) considers both the above to be Cyclothone larvae belong to the group with slope species, whose reproduction might be vertically extended distribution and a subsurface favoured by the current system. maximum (John, 1984b and literature there). The distribution of neustona Scomberesocidae The larvae should therefore be less affected by has been given in figure 3, anti reveals a surface drift and occur farther to the esst than consistent "scomberesocid hole" off Mauritania Scomberesocidae. This is demonstrated by Cyclo during the winters of 1970, 1977 and 1983 as thone larvae above the shelf (above bottom well as the spring of 1968. Tile easternmost depths of only 90m) between 31*N and 32*N occurrences off Cope Blanc and at 164N represent (Fig.6), where upwelling took place. Contrary to single larvae, suggesting only extreme limits of this expectation however, off Mauritania, the distribution. None of the other surface larvae easternmost occurrences were even farther to the considered typical for the tropical and warm- west than for Scomberesocidae. temperate open Atlantic (John, 1983) were found While several surface species are excellent during these surveys, but during autumn 1972 indicators for surface drift, Cyclothone larvae plankton tows unlikely to catch surface species in the Mauritanian province should be Indicators revealed the presence of some of them (Bendixen, for advection of near-surface (IO? - 60m in 1977). eutrophic areas?) oceanic water masses. Patterns Surprising Is the absence of larvae of the genus of relative abundance in the material under Cyclothone (Fig.6), since edults are regularly investigation (I6*N - 2!*N, coast to 20*W), caught from the depths of the open ocean as well as combined with information on relative age, may -154- proye if a connecting link exists between the : 72-78. Canary Current and the slope off Cape Verde. The -HAGEN, E. & R. SCHEMAINOA, 1964. Der Guineadom offshore link proposed for south of Cape Blanc is im ostatlanlischen Stromsyslem. Beiir. Meeresk., not evident, unless offshore deflection of 51 : 5-27. /i.,punctatum (Fig. 4 for 1983) is so inter -HAMANO I., H. C. JOHN & E. MITTELSTAEDT. 1981. preted. The latter conclusion is not convincing, 8s Hydrography and its effect on fish larvae in the M.punctatum is an "oceanic" species. Mauritanian upwelling area. Deep-Sea Pes., 28A The Mauritanian province is a promising area (6): 561-575. for the investigation of the effect of larval drift on -HARTMANN, J.. 1970. Verteilung und Nahrung des Ichlhyoneuslon im subtropischen Nordoslatlantik. ichthyogeography, it offers distinct peculiarities, 'Meteor‘ Forsch. Frgebn., OS: 1-60. adequate indicator species, good hydrographical -JOHN, H.C., 1973. Oberflâchennahes Ichthyoplanklon data and biological material especially obtained to der Kanarenslrom-Region. 'Meteor" Forsch. test existing theories. Frgebn.. D /5: 36-50. -JOHN, H. C., 1979. Regional and seasonal differences in ichtyoneuston off Northwest Africa. ACKNOWLEDGEMENTS 'Meteor" Forsch. Frgebn., D 29: 30-47. -JOHN, H. C., 1983. Quantitative distribution of fry Part of the data for this study were entrusted to of beloniform fishes in the Atlantic Ocean. "Meteor" me by J. Hartmann and W. Nellen. B. R. Bendixen Forsch. Frgebn., D 36 : 21-33. and H. Weikert provided sorted material. D. -JOHN, H. C.. 1984a. Drill of larval fishes in the Burkei, K. Hülsemann, E. Mittelstaedt and R. S. ocean: Results and problems from previous studies and a proposed field experiment, n : J. D. Mcdeave, Scheltema made critical comments on the G. P. Arnold, J. J. Dodson & W. H. Neill (eds): manuscript. Sampling and investigation of the Mechanisms oF migration in Fishes. Plenum material was financially supported by the Puhi. Corp. New York: 39-60. "Deutsche Forschungsgemeinschaft". -JOHN, H. C.. 1984b. Horizontal and vertical distribution of lancelet larvae and fish larvae in the Sargasso Sea during spring 1979. MeeresForsch., REFERENCES J0{3): 133-143. -JOHN, H. C., 1985. Horizontal and vertical -ANDRES, H. 6. 6, H. C. JOHN, 1904. Results of some distribution patterns of fish larvae off NW Africa in neuston net catches in the warmer Central North relation Io the environnent. In: C.Bas, R.Margalef, & Atlantic- Fish larvae and selected invertebrates. P.Rubies (eds). Simposio internacional sobre MeeresForsch., 30 (3): 144-154. tas areas de af/oramiento mas importantes -ANGEL, M. V.. 1979. Zoogeography of the Atlantic dei oeste africana (Caba Bianco y Benguela), Ocean. In: S. van der Spoel 8» A. C. Pierrot-Bulls 1 .Insl.ln.Pesqueras, Barcelona : 489-512. (eds) Zoogeography and diversity in plankton. -KALININA. Yhi. & A.Y.POOOSINNIKOV. 1970: Bunge Scientific Publishers, Utrecht: 168-190. Qualitative composition and seasonal changes in the -BACKUS, R. H„ J. E. CRADDOCK. R. L. HAEDRICH k Canary Current ichthyoplanklon. J. ichthyoi., /6 B. H. ROBISON, 1977 : Atlantic mesopelagic zoogeo (3): 495-500. graphy. Mem. Sears Fdn. mar. Pes., i (7) : -KALININA. E. M. & V.A. SEBLETSKAYA, 1979: The 266-287. qualitative composition and distribution of ichthy -BENDIXEN, B. R., 1977. Untersuchungen an oplanklon off the coast of Mauritania. J. ichthyoi., Fischiarven vor Nord-West -A Frik a zwische:, !9i4): 146-150. Cap Barbas und Cap Vert. Thesis, Kiel Univ., -KILIACHENKOVA, V. A, 1970: Development and mimeogr: 101pp. distribution of eggs and larvae of Trachurus -OHI 1967. Monatskarlen Fur den Nord- trachurus L.. Rapp. P. -v. Reun. Cons. perm, at/antischen Ozean. Deutsches Hydrographisches int. F ftp/or. Mar. 159: 194-198. Institut, Hamburg. -MAURIN, C., 1968: Ecologie ichtyologique des fonds -HA6EN, E„ 1981. Mesoscale upwelling variations off chalulables Atlantiques (de la Baie Ibero-Marocaine à theWe5t African coast. Coast, estuarina Sei., i la Maurétanie) et de la Mediterranée Occidentale. -155- Pev. Trav. /nsl. Pech. marii., 32 (\): 1-147. North-West Africa in February. iCES.C.M., -MICHELSHEN, N„ 1984. Interannual upwelling /97/il 5: 4pp. variations off NW-Africa and the influence of the -WOOSTER. W. S.. A. BAKUN & D. R. MCLAIN, 1976. "Southern Oscillation". ICES, C hi., 1984Z, 2/ : The seasonal upwelling cycle along the eastern 15pp. boundary of the Nori Atlantic. J. mar. Pes., 3d -MITTELSTAEDT, E., 1974. Some aspects of the (2): 131-141. circulation in the Northwest African upwelling area off Cape Blanc. Tethys, 0(1-2) : 89-92. -MITTELSTAEDT, E., 1983. The upwelling area off Northwest Africa.- A description of phenomena related Io coastal upwelling. Prog. Oceanogr., 12 : 307-331. -NORCROSS, B. L. & R. E. SHAW. 1984. Oceanic and estuarina transport of fish eggs and larvae:A review. Trans. Am. Fish. Soc., i tJ (2) : 153-165. -POWER. J. H., 19B4. Adveclion, diffusion, and drift migrations of larval fish. In: J. 0. (leeleave, 6. P. Arnold, J. J. Dodson & W. H. Neill (eds): Mechanisms of migration in Fishes. Plenum Publ.Corp.New York: 27-37. -RICHERT, P„ 1975. Die raum/iche Verteiiung und zeii licha Fntwickiung des Phytoplanktons, mii hesonderer Berück- sichtigung der Pialomeen, im iii. W. - afrikanischen Auftriebsgebiet. PhD thesis. Kiel Univ., mimeogr: 140pp. -SEDLETSKAYA. V. A.. 1975. The dynamics of maturation of the horse mackerel Trachurus trachurus from different regions of the Central-Eastern Atlantic and the distribution of spawning grounds depending on the seasonal position of the hydrologic frontal zone. J. ichtyoi.. 15(2) : 239-245. -SEDLETSKAYA, V.A., 1983a. Ichthyoplanklon of the Atlantic Ocean at the Northwestern African Coast. J. ichtyoi., 23(5) : 150-153. -SEDLETSKAYA. V. A.. 1983b: Fluctuations in abundance of sardine (Sardina pilchardus Walb., 1792) eggs and larvae along the Atlantic coast of Morocco. Trudy Allani. NiRO : 3-9. -SEDYKH, K. A., 1978. The coastal upwelling off the Northwest Africa. iCES.C.M., 1978/Z 12 \ 16pp. -SHAFFER, 6„ 1976. A mesoscale study of coastal upwelling variability off NW Africa. ‘Meteor" Forsch.Ergebn., A !7\ 21-72. -STRAMMA, L.. 1984. Wassermassenausbreilung In der Warmwassersphaere des subtropischen Nordostatlantlks. Ser. tnsl. Meereskunde. Kiel 125: 108pp. -WIKTOR. K., 1971. Biomass of zooplankton and distribution of fish larvae in the shelf waters off -156- POLYTYPY, BOUNDARY ZONES AND THE PLACE OF BROADLY-DISTRIBUTED SPECIES IN MESOPELAGIC ZOOGEOGRAPHY ROBERT KARL JOHNSON Field Museum of Natural History, U.S.A. INTRODUCTION BROADLY-DISTRIBUTED SPECIES For those mesopelagic species whose distribution While there are broadly-distributed species that lies entirely within the warmwater regions of the show within-ocean concordance with recognized ocean (ca. 40*N to 40*S), it is heuristically species assemblage areas (Johnson, 1982; useful to distinguish two major distribution Johnson & Glodek, 1975), there are many patterns (e.g. Brinton, 1962; Ebeling, 1962; broadly-distributed species thai in contrast are 1967; Johnson, 1974; 1982): widely-distributed throughout most of the 1. species relatively restricted in distribution, tropical-subtropical area of ali three ocean limited to one ocean basin and generally limited to basins. For example Yan Soest ( 1979) tallied data ali or part of one water mess region (refers to for 957 oceanic zooplankton species and showed geographic area underlain by a principal upper broad to very broad distributions (crossing water water msss as depicted by Sverdrup et al., 1942: mass boundaries) for two-thirds or more of the 740). mesopelagic species for which he had data. 2. species more widespread, with distributions Johnson (1974; 1982) showed that among 17 crossing water msss boundaries, typically in two warm-water scopelarchids and evermannellids, or three ocesn basins, exhibiting varying six species, ali in the Pacific, are restricted in approaches to warmwater cosmopolitanism (see the sense used above; three species, ali equatorial, Johnson, 1982: 185 for subcategories; aiso see occur in just the Indian and Pacific Oceans Ebeling, 1967; Fleminger &Hu1semann, 1973). (paralleling results of Fleminger & Hulsemann, Most attention in pelagic biogeography hss 1973; Judkins, 1978; and others); and ten focused on species relatively restricted in species occur in ali three oceans. This proportion distribution and such focus hss resulted in of three ocean species is by no means to these two discovery of distinct and discrete open-ocean families (see Gibbs et al., 1983: 119 for species assemblages, recognized by concordance in extensive documentation). It is sufficiently relatively restricted distribution of species from common that Ebeling (1967) recognized a diverse taxonomic groups and trophic levels catchall "Circumcentral-Tropical" Primary (Parin, 1970; McGowan, 1971; 1974; 1977; Zoogeographic Region incorporating ali oceanic Johnson, 1982; Brinton & Gopalakrishnan, warm-water areas except the Mediterranean and 1973; Backus et al., 1977). Such assemblages eastern tropical Pacific. McGowan (1974: 15) constitute the open-ocean equivalent of the lumped spécies broadly-distributed in the Pacific "biotas" of the vicariance biogeographer3 (Croizat into a "Cosmopolite Fauna", broadly overlapping et al., 1974), but their study by open-ocean other recognized warmwater faunal regions. workers has been almost entirely ecological in Such "waste-basket" treatment typifies the orientation (Johnson, 1982: 174). The number "place" of broadly-distributed species in discuss of patterns ("ecosystems" in McGowan, 1971; ion of pattern in open-ocean distribution: they are 1974; 1977; "assemblages" In Barnett, 1983; essentially ignored. This results from at lesst "provinces - regions - distribution-patterns three factors: lack of material, dearth of syn arcas" in Backus et al., 1977) is apparently both optic systematic studies world-wide in scope, and finite and rather small. lack of conceptual framework, a set of working -157- hypothesis regarding the "fit" of broadly- thorough documentation: lack of adequate sampling distributed species. coverage-horizontally, vertically and temporally; Barnett ( 1975: 36; 1984: 207) presents a and secondly frequent inability to distinguish plausible framework of ecological / biogeo- ecophenotypic effects from differences related to graphical hypotheses relevant to broadly - genetic divergence (Brinton 1962: 178; 1975: distributed species and cites possible examples 210). (Table I). In the present paper only the "eucosmospolite" category is considered. Here the working hypothesis is that broadly-distributed THE HYPOTHESIS OF POLYTYPY species are comprised of separable, genetically- distinct populations, the differences reflecting Reflecting these problems is a study of meristic adaptation, and, that replacement of these character variation in broadly-distributed meso- populations occurs at the boundary of species- pelagic species, selected on the bssis of assemblage areas. This concept is not new (e.g. occurrence throughout the broadest possible range Brinton, 1962; 1975; McGowan 1971; Johnson of warm-water oceanic habitats (Johnson & & Barnett, 1975; Badcock, 1981; Johnson, Barnett, 1972; 1975). Yalues for selected 1982), but two major difficulties have precluded meristic characters and three measures of "food Table I Categories of broadly-distributed species, with putative examples of each category (modified from Barnett, 1975, 1984) (1 ECOLOGICAL OPPORTUNISTS ~ 1 Build up larga populations only in acotonal anas 2 SPECIES 'BUFFERED* BY DISTANCE FROM PRIMARY PRODUCERS High trophic laval carnivora, filtar = trophic distança Chauliodus sloani, Echiostoma barbatum, Laptostomias hap/ocaulus. Odontostomops normalops, Stemonosudis macrum. Avocettina infans BaLhypalagic zooplanktivoro. Filtar = vertical distmca Poromitra crassiceps, Scopeloberyx robustus. S. opisthopterus, Taaningichthys bathyphilus, Lampanyctus nigar 3 SPECIES EXHIBITING MARKED VARIATION IN ABUNDANCE FROM ONE ECOSYSTEM TO THE NEXT Abundant in gyres, present but rare at equator Siornophyx diaphana. Argyropelecus hemigymnus. Cyclothone pallida. C.alba. Argyropelecus sladeni. Diaphus elucens. D. schmidti. Genostoma atlanticum Abundant at equator, present but rara in gyres Hygophum proximum. Cyclothone acclinidens, Lobianchia urotampa. Danaphos oculatus, Nemichthys scolopaceus A ^COSMOPOLITES' BROADLY-DISTRIBUTED SPECIES NOT SHOWING MARKED VARIATION IN ABUNDANCE FROM ECOSYSTEM TO ECOSYSTEM Notolychnus valdiviae. Lampanyctus stainbocki. Diogenichthys atlanticus, Ceratoscopelus warmingi. Symbolophorus evermanni. Triphoturus nigrescens. Vinciguerria nimbaria -158- availability" were correlated negatively, but no by Badcock (1981: 1488), ".... (while) the relationship with temperature, salinity, or importance of recognizing distinct intra-specific dissolved oxygen could be found. Ecophenotypy was populations and comprehending the nature of their argued against but could not be totally ruled out. differences can not be over stressed... intraspecific Johnson & Barnett ( 1975) hypothesized that the variation in most (mesopelagic) species is (very) observed variation is the result of adaptation of poorly documented." To my knowledge Brinton's egg size, fecundity, snd larval size to differing (1962: 178) classic demonstration of the productivity conditions. They possessed only "forms" of Stylocheiron affine is un limited and indirect evidence for the last of the paralleled by any mesopelagic fish study. three predictions. Relevant to the present paper is the hypothesis thai the observed meristic variation reflects VINCIGUERRIA NIMBARIA: A CASE STUDY genetically distinct, allopatric populations of broadly-distributed midwater species and thai the Partly filling this gap (for fishes) is work in distribution of such populations is congruent with progress on variation in Vinciguerria areas defined by the "generalized tracks" of nimbaria (Johnson & Feltes, 1984; and in assemblages of distributional ly-restricted prep.). There are at least four criteria to species. While the concept of polytypy is hardly establish candidate species for study of polytypy: novel by terrestrial standards, better evidence wide distribution (Fig. 1); apparent "eu- for it among oceanic populations would have cosmopolitanism" , sensu Table I; abundantly important consequences for open-ocean zoo and synoptical ly represented in collections; and geography (eg McGowan, 1971 ; Badcock, 1981). evidence of detectable and quantifiable inter It would tend to negate the apparent and regional variation. Vinciguerria nimbaria unexplained distinction between broadly- was chosen for study because it fits well each distributed vs. restricted species. Division of criterion. V. nimbaria, exhibits demonstrable broadly-distributed species into allopatric region to region variation in morphometric and populations restricted to described faunal regions meristic characters. Especially in gili raker is consonant with the recognition of such regions counts there exists evidence of difference between based on concordantly restricted, rather narrow equatorial vs.central populations (Fig. 2). ranging species. Such intraspecific populations Minimal criteria for establishment of polytypy may differ in aspects of their biology such 8s life for V.nimbaria (in the sense of the compound history "strateg/" (egg and larval size, fecundity, hypothesis advanced above) include: seasonality, etc.) leflecting differences in 1. evidence of consistent differences between biological and/or physical parameters between specimens grouped by species-assemblage areas; regions (e.g. McGowan, 1971 ; Johnson & Barnett, 2. evidence that boundaries between “forms" 1975; Reid et al., 1978). The point is well made (exact taxonomic status to be determined) are Fig. 1 Distribution of samples of Vinciguerria included in this study. Ali specimens are V.nimbaria except those labelled RDS (= V.mabahiss Johnson & Feltes, 1984) and LUC (= V. lucetia Garman, 1899). Stippled bands denote areas transitional between water mass regions as depicted by Sverdrup et al. ( 1942). Solid lines (Atlantic only) indicate boundaries between regions recognized es mesopelagic faunal regions by Backus et al. ( 1977). Atlantic areas include: CNA = subtropical North Atlantic (Including Caribbean Sea and Gulf of Mexico); EOA = tropical Atlantic including Mauritanian Upwelling Region; CSA = subtropical South Atlantic. Closed circles are Vnimbaria stations in central water msss regions (= "Central"). Open circles are V.nimbaria localities in equatorial water mass regions ( = "Equatorial"), except Atlantic and South China Sea (see Johnson & Feltes 1984). Closed squares are V. mabahiss localities. Open squares are V. lucetia localities. -160- concordant with boundaries between described S7 M S9 60 61 6? 63 64 6S 66 67 63 69 70 7) 77 73 17 0Œ000 species assemblage areas; note that "boundaries" CENT. 00QI0 are in fact transition z'vies thai may vary from 19 0 p3 03 0 ED 0 narrow snd sharp (Johnson 1982: 225) to rather TO diffuse and broad (McQowan 1977: 425); 7» 3. evidence thai differences used in 27 ® © © @® © m distinguishing "types" are not ecophenotypic in 23 origin. 24 Material from two transects involving the 25 26 crossing of known faunal boundaries, with 27 V.nimbaria abundantly taken on each, has 28 provided limited data relevant to these criteria. 29 The ANTIPODES transect (Johnson & Barnett, 30 1975) of August-September, 1970, offers 31 limited support. V.nimbaria was taken at 19 3? stations in the Philippine Sea and at 6 stations in 33 the South China Sea. A sharp model shift in 34 photophore and vertebral counts and especially in ft gili raker counts (Johnson & Barnett 1975: Fig 36 4, Tables 6,7,9) distinguishes specimens from the two areas while counts appear within-area homogeneous. The 3hift coincides geographically Fig. 2 Total body photophores tallied by gili raker with a well-eslablshied faunal "boundary" numer (total on first gili arch) for specimens of separating equatorial (tropical) species (South Vinciguerria . Explanation of "Central" vs China Sea) from central (subtropical) species "Equatorial" given in legend to figure 1. (Philippine Sea) (e.g. compare the distribution of the euphausiid Thysanopoda obtusifrons^^ thai of the Indo-Australian "forms" of Substantial overlap occurs In ali other Stylocheiron affine in Brinton, 1975). examined characters although some hint of Overlap in character values and relative lack of equatorial/central separation is suggested by South China Sea material preclude certain principal components analysis of a 21 character identification of specimens in the apparent zone of morphometries dats matrix ( F ig. 3). sympatry at stations 21 and 22 ( Johnson & In November, 197U, the Woods Hole vessel Barnett 1975)(fig. 4) - muddying the picture. ATLANTIS II ran a double transect from central to More convincing is newly-obtained evidence equatorial and back into central. Three recognized from the Atlantic. Specimens of V. nimbaria Atlantic faunal regions (sensu Backus et al., were studied from throughout the Nori Atlantic 1977) were sampled (Fig. 4): the North Atlantic Subtropical Region (CNA, Fig. 1), most of the Subtropical Region (CNA: CNA6, TCI, TC2, Atlantic Tropical Region (EOA) and 5 stations CNA5), the Mauritanian Upwelling Region (MUR: from the South Atlantic Subtropical Region (CSA) TE) and the northeastern boundary region of the as drawn by Backus et al.( 1977). In gili raker tau nelly- associated Atlantic Tropical Region counts (Table 11 ) there exists absolute difference, (EQA-.TE). On the southward leg ( CNA6 to TOI to north end south central specimens hsve 17 to 21 TE) the shift between central vs. equatorial gili rakers (total, first arch), equatorial "types", as established by gili raker counts (Table specimens have 22 to 26. This difference applies 3), coincided exactly (Fig. 4) with the boundary throughout the CNA, EOA and CSA areas, satisfying between CNA and MUR, es drawn by Backus et the criterion of consistent difference between al.( 1977) Agreement was not as sharp on the areas. northward leg, TE to TC2 to CNA5. At two stations, RHB 2076, RHB 2077, both "types" were taken -161- Table II Number of gili rakers (total, first arch) for Atlantic specimens of Vinciguerria nimbaria. Area designations keyed to figure 1. 6JLL RAKERS ON FIRST 6ILL ARCH Lataiion Nr.StatiMS 17 16 19 20 21 22 23 24 25 26 N X ± « CNA-1 (6) 3 20 7 2 32 19.25 .26 .718 CNA-2 (4) 2 3 3 1 9 18.33 .77 1.000 CNA-3 (IO) 4 8 1 13 18.77 .36 .599 CNA-4 (4) 1 3 4 8 19.38 .62 .744 CU A-5 (6) 2 2 8 1 13 18.62 .53 .870 CNA-6 (5) IO 3 13 19.23 .26 439 CNA-7 (2) 2 6 IS 7 1 31 18.97 .33 .912 CNA-8 (1) 2 8 IO 18.80 .30 .422 CNA-9 (1) 1 8 1 IO V9.10 .52 .738 TOTALS 6 22 83 24 4 139 18.99 .13 .789 TC-1 (9) 1 3 17 9 1 31 19.19 .29 .792 TC-2 (9) 9 23 43 9 84 18.62 .18 .820 TOTALS IO 26 60 18 1 lis 18.77 .16 .849 TT (23) 6 26 44 23 3 102 23.91 .18 .913 EQA-I (1) 3 13 3 1 23 24.22 .32 .736 EQA-2 (1) 3 6 IO 1 20 24.45 .39 .826 EQA-3 (1) 1 6 4 11 24.27 .43 .647 EOA-4 (1) 6 5 1 12 23.58 .42 .669 EQA-5 (1) 4 a 4 1 17 24.12 .44 .857 TOTALS 6 43 02 40 6 185 24.03 .13 .869 CSA-1 (1) 3 17 a 28 19.18 .24 .612 CSA--2 (1) 6 4 IO 19.40 .36 .516 CSA-3.4.5 (3) 1 2 7 4 14 19.00 .51 .877 TOTALS 1 S 30 16 52 19.17 .19 .678 in the same net haul. 200m (Fig. 5) demonstrates the association of the The fit of the equatorial "types" to MUR and EOA equatorial "type" with cooler MUR water. appears better In the north than In the esst (Fig. Accumulating faunal evidence (Krefft, 1974; 4) but this is aiso true for the MUR endemic Backus et al., 1977; Badcock, 1981; Johnson, myctophi, Lampadena pontifex (Nafpaktitis 1982) has established the ONA, EÛA and OSA es et al., 1977: Fig. 120). It most likely reflects the comparable to species-assemblages areas (eco seasonal hydrographic variability of MUR, known systems of McQowan, 1977) in the Pacific. The to be greater in the south MUR (Wooster et al., status of MUR is unusual, for, as noted by Badcock 1976; Badcock, 1981). A plot of ATLANTIS II (1981: 1485), it is the only North Atlantic records for V. nimbaria against temperature at region inhabited by species with northern (sensu -162- ll| 16% -|-- -!«29K B o _ a Q L SP 0 B B _ „ B ©0 Fig. 3 Relative position of 51 specimens of QDa on Q ■ UO GQ ■ Vinciguerria nimbaria in the projection of Q 0 0 B 0<3»Q6g the first two principal components of a a ®Q * Q 21-morphometric character correlation matrix 9 (characters used expressed es proportions of o standard length; characters and methods 8S in —I------1------1------r Johnson & Feltes, 1984). Sguares= equatorial -1.0 o *10 ATLCOR PCI specimens. Circ1es= central specimens. Table III Number of gili rakers (total, first arch) for specimens of Vinciguerria nimbaria from ATLANTIS II. cruise 59. November, 1970. TOTAL 6ILL RAKERS ON FIRST 6ILL ARCH 17 18 1920 21 22232425 26 TOTAL MEAN ± 2021 8 3 C-11 I9.27± 0.31 2024,2025 1 3 2 1 C 7 19.291 1.16 2028.2029,2030 1 6 1 C 8 19.001 0.45 2034.2035 2 8 6 C 16 19.251 0.36 2037,2044.2047 2 2 1 E 5 23.801 1.04 2048,2049.2050 16 5 2 E 14 23.571 0.49 2051 4 4 12 3 1 E 24 23.7110.44 2056.2057.2058.2059 3 7 3 E 13 24.001 0.43 2060.2062 1 4 7 E 12 24.501 0.43 2065.2066.2070 3 5 3 E 11 24.001 0.52 2071.2073 13 7 3 E 14 23.861 0.50 2075 2 111 E 5 24.201 1.62 2076 2 3 7 4 2 C16 18.811 0.52 E 2 2077 16 7 1 1 1 C 15 18.531 0.41 E 2 2080.2081 3 6 2 1 C 12 1B.081 0.57 2082.2083.2084 3 7 20 1 C 31 18.611 0.26 2085 1 7 2 C IO 10.101 0.41 2088 1 4 1 C 6 18.831 1.03 CENTRAL TOTALS 1126 7222 1 132 EQUATORIAL TOTALS 6 26 44 23 3 102 " Station positions given in Fig. 4 (C= Central, E= Equatorial). -163 Fig 4 Distribution of samples of Vinciguerria • JMJ nimbaria taken by the ATLANTIS II, Cruise 59, November, 1970. Four digit numbers are Richard H.Backus (RHB) station numbers (Woods Hole Oceanographic Institution). Area designations 8s in figure I. The wide stippled band indicates the zone of transition between the North Atlantic and South Atlantic Central Water Msss Regior as depicted by Sverdrup et al.(1942). The solid lines indicate the boundary between the North Atlantic Subtropical Region, Mauritanian Upwelling Region and Atlantic Tropical Region es depicted by Backus et al. ( 1977). Closed circles = "Central" specimens; open circles indicate "Equatorial" specimens. The partly closed circles indicate the two stations where both "types" were captured in the same haul. See text for explanation. ’ Backus et al., 1977), subtropical and tropical distribution patterns. For V. nimbaria es for the pair Coccorella atlantica vs Scopelarchus CONCl USIONS guentheri (Johnson 1982: Fig 54) MUR is faunally associated with EOA. Thus the available I conclude thai in the Atlantic, at least, data 3how that V. nimbaria satisfies the criteria Vinciguerria nimbaria is polytypic and sur of difference and boundary concordance. mise that this is true throughout its range. I Evidence for the criterion of genetic distinction predict that additional stud/ will show this to be a is, 83 usual, limited, gili raker counts (Table II) more general condition among mesopelagics than are homogeneous throughout the quite large CNA now known, whatever the taxonomic status of the vs EOA vs CSA areas, but shift dramatically (Table "types" recognized (see Gibbs, this volume), to III) at the boundaries crossed by the AT LANTIS11 the extent that this prediction is true, will the transect; the material examined from CNA was apparent disparity between broadly-distributed collected throughout the yearly cycle; and the and narrowly-restricted open ocean midwater ATLANTIS II transect material Tor both CNA and species diminish. EQA+MUR contained specimens from throughout the size-frequency spectrum. Fig.5 Plot of temperature at 200m by "type" of U - Vinciguerria nimbaria taken during Cruise 59 of the ATLANTIS II while occupying the stations depicted in figure 4. Circles = "Central", squares= "Equatorial", closed circles Indicate the two stations (2076+2077) where both "types" were taken in the same net haul. -164- REFERENCES Biology of the Indien Oceen. Springer-Verlag, New York: 339-347. -BACKUS, R. H. & J. E. CRADDOCK, 1977. Data report -GIBBS. R. H.. Jr. T. A. CLARKE & J. R. GOMON, for Atlantic pelagic zoogeography. Woods Hole 1983. Taxonomy and distribution of the stomioid Oceenogr. last., lech. Rep., No. WHQt-77 : genus Eustomias (Melanostomiidae), I. Subgenus 78 pp (mimeo). Nominoslomias. Smithson. Contr. Zoo!., 380 : iv -BACKUS. R. H.. J. E. CRADDOCK, R. L. HAEDRICH 8, + 139 pp. B. H. ROBISON, 1977. Atlantic mesopelagic zoo -JOHNSON, R.K., 1974. A revision of the alepisauroid geography. tlem. 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An inverse PP- correlation between meristic characters and food -BARNETT, M. A.. 1983. Species structure and supply in midwater fishes: evidence and possible temporal stability of mesopelagic fish assemblages in explanations, fish Bull., US.. 73(2): 284-298. the Central Gyre of the North and South Pacific Ocean. -JOHNSON. R. K. 8. R. M. FELTES, 1984. A new tier. Sio/.. 7d: 245-256. species of Vinciguerria (Salmoniformes : Photichthy -BARNETT. M. A.. 1984. Mesopelagic fish zoogeo idae) from the Red Sea and Gulf of Aqaba, with graphy in the central tropical and subtropical Pacific comments on the depauperacy of the Red Sea Ocean: species composition and structure at mesopelagic fish fauna, fie/diene Zoo/., new Ser., representative locations in three ecosystems, her. 22 : yi + 35 pp. Sio/., 62. 199-208. -JOHNSON. R. X. & G. S. GLOOEK, 1975. Two new -8RINT0N, E., 1962. The distribution of Pacific species of Evermannella from the Pacific Ocean, with euphausiids. Bull. Scripps Inst. Oceenogr, 8 notes on other species endemic Io the Pacific Central (2): 51-270. or Pacific Equatorial Water Masses. Copeie, 1975 -BRINTON, E., 1975. Euphausiids of southeast Asian (4): 716-730. waters. Nege Rep., V (5): 287 pp.. -JUDKINS. D. C.. 1978. Pelagic shrimps of the -BRINTON. E. 8, K. GOPAl.AKRISHNAN, 1973. The Sergestes edwardsii species group (Crustacea, distribution of Indian Ocean euphausiids. In: B. Decapoda, Sergestidae). Smithson. Contr. Zoof, Zeilschel & S. A. Gerlach (eds). The Biology of the 256 : 34 pp. Indien Oceen. Springer-Verlag, New York: -KREFFT, G., 1974. Investigations onmidwaler fish in 357-381. the Atlantic Ocean. Ser. dt. Wiss. Kommn -CROIZAT, L. G. NELSON & D. E. ROSEN, 1974. Meeresforsch., 23 : 226-254. Centers of origin and related concepts. Syei. Zoo!.. -MCGOWAN, J. A. ,1971. Oceanic blogeography df the 23 (2): 265-287. Pacific. In: B. M. Funnel 8. W. R. Riedel (eds). The -EBELING, A. E.. 1962. Melamphaidae I. Syslematlcs Micrope/eonto/ogy of the Oceans. Cambridge and zoogeography of the species in the balhypelagic Univ. Press: 3 - 74. fish genus Melamphaes Guenther. Dens Rep., 58 : -MCGOWAN, J. A.. 1974. The nature of oceanic 164 pp. ecosystems. In: C. B. Miller (ed). The Biology of -EBELING, A. E.. 1967. Zoogeography of tropical the Oceanic Pacific. Prot. 33rd Annual Biol. deep-sea animals. Stud. Trop. Oceenogr. Miami, Cooloq., Oregon State Univ. Press, Corvallis : 9-28. 5 : 593-613. -MCGOWAN, J. A., 1977. What regulates pelagic -FLEMINGER, A. 8, K. HULSEMANN, 1973. Relationship community structure in the Pacific? In: ^Anderson 8i of Indian Ocean epiplanktonic calanoids Io world B.J. Zahuranec (eds). Oceanic Sound Scattering oceans. In: B. Zeilschel & S. A. Gerlach (eds). The Prediction. Plenum Press, New York: 423-443. -165- -PARIN, N. V., 1970. Ichthyofauna of the eplpelaglc zone. Inst. OceanaI. Acad. Sei.USSR. Israel Progr. Sei. Transi. M.RAVEH. transi. : 206 pp. -REID, J. L, E. BRINTON, A. FLEMINGER, E. L. VENRICK & J. A. MCGOWAN. 1978. Ocean circulation and marine life. In: H. Charnock &, G. E. R. Deacon (eds). Advances in Oceanography. Plenum Press, New York: 65-130. -SVERDRUP. H. U.. M. W. JOHNSON 6, R. H. FLEMING. 1942. The Oceans, Their Physics, Chemistry and General Biology. Prentice-Hail, New York: 1087 pp. -VANSOEST, R. W. M„ 1979. North-south diversity. In: S. van der Spoel & A. C. Pierrot-Bulls (eds). Zoogeography and Diversity of Plankton. Bunge scient. Puhi., Utrecht: 103-111. -WOOSTER. W. S„ A. BAKUN & D. R. MCLAIN. 1976. The seasonal upwelling cycle along the eastern boundary of the North Atlantic. J. mar. Pes., 3d (2): 131-141. 166- BIOGEOGRAPHY OF THE HUMPBACK WHALE, MEGAPTERA NOVAEANGLIAE, IN THE NORTH ATLANTIC STEVEN K. KATONA College of the Atlantic, Bar Harbor, U.S.A. INTRODUCTION schooling tisii (herring, Clupea harengum capelin, Mallotus villosus, and sand lance, Current studies on the humpback whale Ammodytes americanus in Ule North Atlantic) Megaptera novaeangliae offer insights into pius krill, especially Meganyctiphanes nor baleen whale biogeography and show great vagica. Prey type, abundance and distrib- ution contrasts to the other organisms treated in this influence local feeding behaviour (Hain et symposium. Each of the approximately 5500 al.,1982; Baker & Herman 1985) and humpback whales (Balcombet el., 1985) in the distribution on the summer range. For example, North Atlantic Ocean commands, on average .about short term and year-to-year changes in 54,000km3 of water and 13,740km2 of ocean Newfoundland humpback distribution are related surface. Each individual is large (up to 19m to changes in capelin abundance and distribution long), potentially long-lived (up to 50 years or (Whitehead & Carscadden, 1985), but many more), fast (up to IO knots) and able to swim Individuals remain throughout the summer at through the various water masses of an entire Stellwagen Bank, Massachusetts, to feed upon a ocean basin. Large size, long lifetimes and large resident population of sand lance currently in potential ranges buffer individuals and the high abundance (Mayo, 1982). Fine-scale population from seasonal and other short-term distribution is aiso affected by the whales’ ability environmental changes. Considering such to recognize individuals and respond to them capabilities, what factors limit the distribution of differentially. Some humpbacks have been seen this species and other baleen whales ? togetlier over much of a feeding season, and occasionally during several feeding seasons (Baker & Herman, 1985; Weinrich, 1983; THE HUMPBACK D.Matilla, pers. comm.). Factors underlying such associations could be 8s mundane 8s similar sizes, Tracking whales individually-identified by swimming speeds, diving capabilities, or photographs of distinctive markings, has revolut physiological states, but kinship could aiso be ionized study of their distribution and ecology. Ali involved. individuals are potentially recognizable by this Humpbacks do rai eat during winter while relatively inexpensive, benign (Payne, 1983) gathered to calve and mate within 20 degrees of technique . Humpbacks are distinguished by the equator in clear, poorly-productive, shallow, individual variations in the black and white warm water (about 25*0 at banks or bays pattern of the ventral side of the flukes ( Katona & protected from heavy surf by coral reefs or other Whitehead, 1981). Population size con be geologic features. Large whales may occasionally estimated by applying mark-recapture techniques overwinter in cold water, but the 5m long (Seber, 1972; Balcomb et al., 1985) to the newborn calves are born in the warmest waters photographic collection. known to be used for breeding by any baleen As do nearly ali baleen whales, humpbacks whale. Perhaps the long flippers, each about one migrate annually between productive high latitude third of the body in length, would in colder water summer feeding ranges, mainly on or along drain heat from the thin newborn at an intolerable continental shelves, and lower latitude winter rate. Later In Ute the flippers will be used to breeding ronges. Their flexible diet includes manoeuYer, herd fish, guide calves, pound -167- aggressively on the water or on other whales, Table I Distribution of photographs of humpback possibly clasp a partner during mating (not yet whale flukes contained in Atlantic Humpback observed) and, ironically, to dump excess heat Whale Catalogue es of May 15,1985. while in warm waters (Brodie, 1975). Concentr ation of female humpbacks at traditional calving EUROPE IO sites attracts males for mating. "Rowdy" groups of NE ATLANT 0 males vie for dominance, competing physically ICELAND 18 and with sound for access to females ( Tyack & OREENLAND 149 Whitehead, 1983; Baker & Herman, 1984). NFL D/LAB 1413 Males may select smooth bottom topography to G.ST.LAWR 97 optimize sound propagation (Whitehead & Moore, 0OM/N.S 340 1982). U.S.COAST 3 Analysis of photographs of over 3500 individual BERMUDA 73 humpbacks from the North Atlantic (Table I) and SILVER BK 976 over 900 resightings of identified Individuals PRTO.RICO 474 (Table II) reveal that this population comprises VIRGINS IO at least four, and probably five, separate feeding substocks (Iceland-Denmark strait; western Greenland; Newfoundland-Labrador; Gulf of St. total 3563 Lawrence; and Gulf of Maine - Nova Scotia) to which high percentages of individuals return annually (Table III). No interchange has yet been recently been seen in both the Gulf of St.Lawrence observed between the first three units and only and the Gulf of Maine. one whale has been seen in both Newfoundland and Table II aiso shows thai Individuals from ali five the Gulf of Maine. Less clear is the situation in the of the feeding substocks migrate to the Antilles Gulf of St. Lawrence. Some humpbacks return during winter for breeding (Katona et al., there annually (Table III), but ten whales have 1985a). Chi-square analysis shows that a been seen in both the Gulf of St.Lawrence and in constant proportion of whales from each of the Newfoundland; and nine different whales have five northern regions visus the winter range Table II Geographical distribution of resightings of individually-identified humpback whales from the North Atlantic. Within-region resightings are for intervals of one year or longer. 1 G N L M U B S P V A E ICELAND 0 GREENLAND 0 43 NFLD/LAB 0 0 205 G.ST.LAWR. 0 0 IO 20 ------60M/NS 0 0 11 9 201 ------E.COAST,US. 0 0 0 0 1 0 ------BERMUDA 0 2 IO 1 7 1 1 -- - - - SILVER BK 1 15 142 7 25 0 8 40 -- - - PTO.RICO 3 1 63 11 15 0 3 40 24 - - - VIRGIN IS. 0 1 0 0 0 0 0 0 1 0 -- N.ATLANTIC 0 0 0 0 0 0 0 0 0 0 0 - EUROPE 0 0 0 0 0 0 0 0 0 0 0 0 _ T_. ■ ■ . _ _ _ _ . ______...... _ ___ . ______. -168- Table III Within-reglonyear-to-year resightings currently depleted or abandoned portions of the of individually-identified humpback whales. historical range (Mitchell & Reeves, 1983) can be recolonized. Factors such as preemption by Location Returns Total No. Percentage human activities; overall population trend; habits of site-fidelty displayed by individuals; extir ICELAND 0 18 0.00 pation of groups making traditional use of 6REENLAND 43 149 28.86 particular locations; and transmission of NFLD/LAB 205 1413 14.51 information about migration paths from mother to G.ST.LAWR 20 97 20.62 calf will certainly be involved. eon/N.s. 201 340 59.12 BERMUDA 1 73 1.37 BRIEF BIOGEOGRAPH I CAL COMMENTS ON OTHER SILVER BK 40 976 4.10 BALEEN WHALES PRTO.RICO 24 474 5.06 Ten species of Mysticeti exist. Ali six members of the family Balaenopteridae (Balaenoptera (Silver Bank, Puerto Rico, Virgin Islands and musculus, blue; B. physalus, finback; B. further south) and aiso the major breeding borealis, sei; B. edeni, Brydei; B. location, Silver Bank, which may now host up to acutorostrata, minke; pius Megaptera 85* of western North Atlantic breeding hump novaeangliae, the humpback whale) inhabit the backs (Winn et al., 1975). However, whales from North Atlantic, North Pacific and Southern Ocean. both Iceland and the Oulf of St.Lawrence appeared Each ocean basin probably contains a separate to be significantly over-represented at Puerto population of each species. Inter-ocean gene flow Rico. Further studies on the Antillean breeding must be high enough to prevent spéciation, but range are needed to discover whether whales from low enough to promote sub-specific morphological the different feeding substocks or individuals of differences within nearly ali species. The different ages or classes use different portions of Balaenopteridae may have originated from the habitat. Starting in late March, humpbacks Miocene Cetotheres (Barnes et al., 1985), migrate north, passing Bermuda (Table II). evolving and radiating in warm waters of the Sighting of an Iceland whole at Bermuda during North Atlantic, probably in the Middle Miocene, April, 1985 (O.Stone& S.Katona, unpubl. data), then crossing the equator to the Southern Ocean shows that some whales from each feeding and the Central American seaway to the North substock migrate past that island. Pacific (Gaskin, 1982: 238). Ali species but B. Payne & Katona ( 1985) presented evidence to «/^/responded favorably to climatic cooling and suggest that each ocean basin, Including the North extended their ranges to high latitudes. None of the Atlantic, is inhabited by one genetic stock of species in the genus Balaenopterae known to humpbacks. This oppers true for the western aggregate for mating or calving. The low frequency North Atlantic, at least, where out of eight "rowdy calls of blues, finbacks and minkes, at least, groups" observed at Silver Bank that contained potentially carry for great distances end would be two or more whales known from the northern suitable for communication between Individuals range, six contained individuals from two scattered on a breeding range (Payne & Webb, different feeding substocks (Katona et at., 1971). 1985b). Additional photography of humpbacks Distribution Is restricted Tor the other three from the eastern North Atlantic is needed in order species. The gray whale (Eschrichtius to discover whether those whales breed in the robustus), the monotypic representative of the western North Atlantic (Christensen, 1984) or at family Eschrichtidae), is unique in several some location in the esstern sector, such as the respects. Its fossii history can only be traced back Cape Verde Islands. to the late Pleistocene (Barnes et al., 1985). Long term observations should reveal whether Living gray whales are known only from the North -169- Pacific. The presence of sub-fossil Atlantic the different species feed in different manners remains ( Mead & Mitchell, 1984) and the lack of (Watkins & Schevlll, 1979) except perhaps In pre-Pleistocene fossils in California suggest the Antarctic when ali feed on krill. Actual colonization from the Atlantic via the Arctic Ocean mixed-species groups are rare. Appreciable during the last warm period (Oaskin, 1982: interspecific separation, as well as intraspecific 238). No record of the species exists from the separation of different sizes or classes of Southern Ocean. The gray whale’s annual 4000 individuals, have been observed In the southern mile journeys between Bering Sea feeding grounds oceen (Laws, 1985) and whaling-related changes and Baja California breeding lagoons are the in pregnancy rete and age of first reproduction for longest known for any mammal. It Is the only some species suggest decreased competition for baleen whale known to feed primarily by sucking krill. Mitchell (1974) hypothesized thai compet up benthic infsuna (Nerini & Oliver, 1983), a ition by sei whale's for copepods mey limit the feature that may limit it largely to soft, shallow, recovery rate of North Atlantic right whale productive feeding locations. populations, but fish, basking sharks and some The family Balaenidae, the oldest of the modern invertebrates could be equally strong competitors. my3ticete families (Lipps & Mitchell, 1976), Recent studies using individual photo displays a curious mixture of biogeographical identification suggests that minke whales distributions. The right whale (Eubalaena (Dorsey, 1983) , blue whales (R. Sears, pers. glacialis) is distributed in the balaenopterid comm.) and finback whales (M. Pratt, pers. pattern, and is the only species besides grey comm.) return annually to habitual feeding areas. whales and humpbacks known to aggregate for Some of the minke whales studied by Dorsey breeding in coastal waters (Payne, 1976). The ( 1983) apparently patrolled home ranges. So far bowhead ( Balaena mysticetus) is Arctic and no evidence exists for Interference-type circumpolar, with no known Southern Ocean competition. remains. But the poorly known pygmy right whale ( Caperea marginata), is circumpolar in cold- temperate waters ( 5* to 20*C) through out the CONCLUDING REMARKS Southern Ocean, with no known northern remains. Some authors give this species family status œ The first cetaceans (Archaeoceti) appear to have Neobalaenidae (Barnes et al., 1985). Balœnids evolved from a group of early Eocene condylorths are specialized to eat small zooplankton at the (family Mesonychidae) that gradually invaded surface, at depth, and sometimes at the bottom. shallow productive bays of the eastern Tethys Sea Right whales and bowheeds require patches of high to feed on fishes (Gingerich et al., 1983; Barnes productivity to survive (Kenney et al., in the & Mitchell, 1978)). By the middle Oligocène the press) and these species may be tied more closely Mysticeti mode of feeding was already fully to productivity-enhancing oceanographic features evolved and the group was probably present in ali than is the case for fish-eating baleen whales. oceans ( Whitmore & Sanders, 1976). Radiation of Strong ecological and morphological differences both Odontoceti and Mysticeti occured in the separate the three living families of mysticetes. Miocene, by which time both groups were fully The three balœnids feed in similar fœhlons, but adapted to aquatic life (Whitmore & Sanders, are separated geographically. The six balae- 1976), and may have occured in response to nopterids are not so clearly separated, but increased ocean productivity stimulated by ecological and geographical differences do exist. As Increased upwelllng (Lipps & Mitchell, 1976). summarized by Nemoto (1971) and Pivorunœ Early mysticetes must have crossed the Equator (1979) the blue specializes on krill, and the during dispersal, but modern mysticetes others feed with varying flexibility or preference apparently do not. Behavioural traits, rather than on fish, krill, copepods and occasionally squid. physiological ability, may prevent modern Several species may feed In the same general area, mysticetes from crossing hemispheres. Many sometimes with whales from another family, but aspects of mysticete behaviour, Including -170- migration, seem to reflect ancestral affinity with individually identified minke whales (Balaenoptera ungulata. Mysticete ancestors were probably acutorostrata) in Washington stale. Can. J. Zoo!., sufficiently large and powerful to avoid random 6i : 174-181. dispersal by storms or currents. If early -6ASKIN, 0. E„ 1982. The ecology or whales ancestors showed group cohesion and fidelity to and dolphins. Heinemann, London and Exeter, New feeding and breeding sites, it is not likely that Hampshire. -BIN6ERICH, P. D., N. A. WELLS, A. E. RUSSELL & S. Equator-like "barriers“ would lave been crossed M. I. SHAH, 1983. Origin of whales in epicontinental any more readily than the/ are today, suggesting remnant seas: new evidence from the early Eocene of that dispersal must have occured along favourable Pakistan. Science, 220: 403-406. paths. If so, detailed paleoecologic knowledge of -HAIN, J. H. W.. 6. R. CARTER. S. D. KRAUS. C. A. surface waters would sited light on early MAYO 8* H. E. WINN. 1982. Feeding behaviour of the dispersals and radiations. Knowledge of early humpback whale (Megaptera novaeangliae), In the dispersal patterns would help explain major western North Atlantic. Fish. Bull., 80 : 259-268. evolutionary divergences at the family level. A -KATONA. S. K. 8, H. WHITEHEAD, 1981. Identifying series of isolating mechanisms is needed to humpback whales using their natural markings. explain evolution of the balaenopterid species Polae Rac., 20 : 439-444. flock if ali six species arose in the North Atlantic. -KATONA, S. K., J. A. BEARD & K. C. BALCOMB, III. Possible factors could Include the behavioural 1985a. The humpback whale fluke catalogue. Final Rep. Natn mar. Fish. Serv. Northeast Fish. balance between site-fidelty, home ranging and Lab. Contract NA-6/-FA-C-00027. January, migratory straying; range expansions and 1985: 22 pp. contractions related towarming or ice formation; -KATONA. S. K„ 6. S. STONE, D. MATILLA, P. J. expansion and contraction of upwelling systems; CLAPHAM & C. A. MAYO. 1985b. Humpback whale and inter-species competition at easily accessible studies on Silver Bank, 1984. Final Rep. Contract productive sites. NMFS 41-USC-252-C-3, Nata mar. Mammal Lab, Seattle. January t985. -KENNEY, R. D.. M. A. M. HYMAN, R. E. OWEN. 6. P. REFERENCES SCOTT & H. E. WINN, (in the press). Estimation of prey densities required by western North Atlantic -BARNES, L. 6. 6 E. MITCHELL, 1978. Cetacea. In: V. right whales. J. Maglio & H. B. S. Cooke (eds) Evolution of -LAWS, R. M„ 1985. The ecology of the Southern A Cri con mammals. Harvard Univ. Press, Ocean. Am. Sei., 7J( 1): 26-40. Cambridge. Ma. : 582-602. -LIPPS, J. H. & E. D. MITCHELL. 1976. Trophic model -8ARNES, L. 6.. D. P. D0MNIN9 & C. E. RAY. 1985. Tor the adaptive radiations and extinctions of pelagic Status of studies on fossil marine mammals. Mar. marine mammals. Pa/aeobio/., 2: 147-155. Mamma! Sei., /(I): 15-54. -MAYO, C. A., 1982. Observations of Cetaceans: -6R00IE, P. F., 1975. Cetacean energetics, an Slellwagon Bank and Cape Bay, 1975-1979. Nata overview of Intraspedflc size variation. Ecology, Techa. InF. Serv. Rep.: 64 pp. 50: 152-161. -MEAD, J. D. 8, E. D. MITCHELL. 1984. The Atlantic -BAKER, C. S. & L. M. HERMAN, I9B5. Whales thai go gray whale. Chap. 2. In: M. L. Jones, S. L. Swartz & Io extremes. Nat. Hist., 04 00) : 52-61. S. Lealherwood (eds). The Cray Whale, -BALCOMB, K. C.. S. K. KATONA & P. S. HAMMONO, (Eschrichtius robustus). Academic Press. N.Y. : 1985. Population estimates for the north Atlantic 33-53. humpback whale using capture-recapture methods on -MITCHELL, E. D„ 1974. Trophic relationships and photo-identified whales, lot. Whoi. Comma. competition Tor food in northwest Atlantic whales. Appendix 5, Annex H. In: M. D. Burt (ed.). Proc. Can. Soc. Zool. Ann. -CHRISTENSEN, I., 1984. A review of humpback whale Meeting, Juno 2-5, 1974. Univ. New Brunswick, (Megaptera novaeangliae) observations In the Fredericton, : 123-133. eastern North Atlantic, lot. Whoi. Comma. -MITCHELL, E. D. ê, R. R. REEVES. 1983. Catch SC/J6/PSIO . history, abundance, and present status of Northwest -DORSEY, E. M., 1983. Exclus! .3 adjoining ranges in Atlantic humpback whales. Rep. Ini. Whoi. -171- Commn. Spec./ss., 5: 153-212. -NEMOTO, T„ 1970. Feeding pattern of baleen whales in the ocean. In: J. H. Steele (ed.) Marine Food Chains. Berkeley, Univ. Calif. Press. : 241-252. -DERINI, M. K. & J. S. OLIVER, 1983. Gray whales and the structure of the Bering Sea benthos. Oecoiogia, 59: 224-225. -PAYNE, R„ 1976. At homa with right whales. Nat. Geogr., !49{3): 322-339. -PAYNE, R., 1983. Recently developed benign research techniques Tor assessing and modeling whale populations. Globa/ ConF. Non-Consump tive Utilization Cetacean Resources, New England Aquarium, Boston, Juno: 15pp. -PAYNE, R. & S. K. KATONA. 1985. A review oT recent evidence affecting stock definitions for hump back whales (Megaptera novaeangliae), fnt. Whoi. Commn, SC/J6/PS 21. -PAYNE. R. & D. WEBB. 1971. Orientation by means of long range acoustic signaling in baleen whales. Ann. N.Y. Acad. Sei., 186: 110-141. PIVORUNAS, A., 1979. The feeding mechanisms of baleen whales. Am. Sei., 67: 432-440. -SEBER, G.A.F., 1973. The estimation oFanimal abundance. Griffin and Co., London : 506 pp. -TYACK, P. & H. P. WHITEHEAD, 1983. Malo competition In large groups of wintering humpback whales. Behavior, 83: 132-154. -WATKINS. W. A. & W. E. SCHEVILL. 1979. Aerial observations of feeding behaviour in four baleen whales, Eubalaena glacialis, Balaenoptera borealis, Megaptera novaeangliae, and Balaenoptera physalus. J. Mamma!., 60: 155-163. -WEINRICH. M., 1983. Observations: the humpback whales oF SteUwagen Bank. Whale Research Press, Gloucester : 145 pp. -WHITEHEAD, H. P. & J. E. CARSCADDEN, 1985. Predicting inshore whale abundance- Whales and capelin off the Newfoundland CGast. Can. J. Fish, egea/. Sei., 42: 976-981. -WHITEHEAD. H. P. 8, M. J. MOORE. 1982. Distribution and movements of West Indian humpback whales in winter. Can. J. Zoo/., 60 : 2203-2211. -WHITMORE, F. C.. JR & A. E. SANDERS. 1976. Review of theOllgoceno Cetacea. Syei. Zoo!., 25 : 304-320. -WINN. H. E., R. K. EDEL & A. 6. TARUSKI, 1975. Population estimate of the humpback whale (Megaptera novaeangliae) in the West Indies by visual and acoustic techniques. •/. Fish. Pes. Bd. Canada, 32 : 499-506. -172- ONTOGENETIC VERTICAL MIGRATION PATTERNS OF PELAGIC SHRIMPS IN THE OCEAN; SOME EXAMPLES TOMOHIKO KIKUCHI Ocean Research Institute, University of Tokyo, Jopen MAKOTO OMORI Tokyo University of Fisheries, Japan INTRODUCTION Pacific off Japan. The sampling method was not the best for the purpose of the present investigation, In many pelagic shrimps, the larvae, juveniles, as the mesh size (5.6mm) was too coarse to and adults are separated vertically and sample larvae and small immatures. Although the horizontally. For example, the principal larval analysis was thus restricted to juveniles and population of a sergastid, Sergestes similis, adults, the results provide information always occurs between 30 and 80m depth both day concerning ontogenetic migration and vertical and night off southern California, but adults distribution. extend to depths of 50 to 600m, through extensive diel vertical migration (Omorl & Gluck, 1979). Horizontal distribution is largely affected by the METHODS ontogenetic migration. The total adult distribution is often much broader than the reproductive Sampling methods have been described in our (viable) range (eg. Colonus cristatus, previous report (Kikuchi & Omori, 1985). Omori, 1967). The picture of biogeography for a Pelagic shrimps were collected at Station B species significantly changes depending on what (30400’N, 147‘00'E; sounding ca. 6200m) developmental stage is studied. during a cruise aboard the R/Y Kaiyo-Maru from Omori ( 1974) reviewed ontogenetic migration June 1 to 25, 1982. Discrete horizontal sampling of pelagic shrimps and concluded that there are was carried out using the KOC sampler with three distributional types, as follows: 5.6mm in mesh size (Anonymous, 1980) at night 1. Species usually living In the eplpelaglc and or daytime, avoiding twilight hours. In ali, 28 upper mesopelagic zones and discharging their tows were made from 17 layers between 150 and eggs in the euphotlc zone where larvae hatch and 6100m depths. The shrimps were sorted, remain Initially. The amplitude of diel vertical identified and counted immediately after being migration increases with growth. caught. The carapace length (CL) from the post 2. Species living In the lower meso- and orbital margin to the median posterior edge of the bethypelaglc zones. The!»' spawning or hatching carapace, was measured to the nearest 0.5mm in takes place in the uppermost part of the vertical ali specimens, except in five species which were range of adult females; the eggs or larvae move either small in size or numbers. upward to the euphotlc zone. The juveniles and adolescents gradually move into deeper water. 3. Species whose spawning, larval and adult life RESULTS AND DISCUSSION take place in the bathypelagic zone. No stages occur In the surface or sub-surface zone. Among the 17,440 individuals collected, 57 In order to verify this conclusion, and to species, representing seven genera of Penaeidea evaluate significance of ontogenetic migration, and twelve genera of Caridea, were identified. relationships between vertical distribution and Acanthephyra quadrispinosa and Sergia growth of a number of shrimps were analyzed prehensilis were the most abundant species and from samples obtained in the northwestern comprised 34.2$ and 12.9* respectively of the -173- Fig. 1 Schematic illustration of four types of ontogenetic vertical migration of pelagic shrimp. total number of specimens. Fourteen other species increases and the shrimps gradually shift to contributed between 7.9 and 1.055. Pelagic greater daytime depths with increasing size. The shrimps could be divided into the following 5 size frequency histogram consists of a single mode types according to their adult diel migration (one year clsss). patterns (Kikuchi & Omori, 1985): Type B - Adults occur in deeper water than larvae 1. Vertical migrants living mainly in the upper and juveniles. The size frequency histogram mesopelagic zone; consists of two or more modes. Diel vertical 2. Extensive diel vertical migrants living in a migration is limited or non-existent. wide range of the mesopelagic zone; Type C - Ontogenetic vertical migration similar to 3. Vertical migrants living in the lower meso Type A, but the size frequency histogram consists pelagic zone; of two or more modes, indicating a life span of two 4. Non- or slight diel migrants of which the years or more. principal population lives in the upper bathy- Type D - Larvae and adults live at the same depth. pelagic zone by both night and day; Size frequency histogram with two or more mode3. 5. Non-migrants living in the lower bathy- and In the present study, ali species of type A were abyssopelagic zones. (Table I). smaller than 17mm CL. Their larvae and Relationships between vertical distribution and juveniles are smaller than 8mm CL. These species growth of twenty species showed existence of four ara mainly epi- and upper mesopelagic sergestids patterns of life h'story and ontogenetic migration and penaeids such ss Sergestes armatus and (Fig.1; Table I). b'jedon the general body shape Sergia scinaltans (Fig. 2). Their lifespan is of pelagic shrimps and size frequency distribution 1.0 to 1.5 years as shown in Sergestes similis of the catch, we found that ali individuals smaller and Sergia lucens (Omori, 1969; Omori & than 8.0mm CL were not quantitatively collected Gluck, 1979). The amplitude of the adult's diel in the present sampling. Line "a" in figure 1 vertical migration covers the greater part of the means 8.0mm CL, and in data interpretation we vertical range of their ontogenetic migration. have assumed that shrimps smaller than line "a" Spawning and/or hatching takes place in the upper were undersampled. layers and larvae feed in the euphotic zone. Type A - The amplitude of diel vertical migration Typa B r epresents the pattern of typical lower -174- Table I The characteristics in vertical distribution of pelagic shrimps. Ontogenetic migration pattern (Typa) Diel vertical migration pattern (Type) Minimum size (CL) of the adult female (mm) Relative abundance in total number of species ( X) Species: Sergestes armatus 5.4 8.1 2 A Sergestes sargassi 2.1 6.6 1 A Sergestes seminudus 1.7 11.4 1 A Sergia japonica 4.2 11.1 4 C Sergia laminata 2.5 7.6 3 A Sergia prehensilis 12.9 8.1 1 A Sergia scintillans 1.9 7.5 1 A Gennadas incertus 6.7 n.d. 2 A Gennadas parvus 2.5 n.d. 3 A Gennadas propinquus 7.9 n.d. 2 A Bentheogennema borealis 0.8 12.4 4 C Bentheogennema intermedia ♦ n.d. 4 8 Oplophorus spinosus 2.1 13.8 1 C Acanthephyra quadrispinosa 34.2 15.8 3 D Notostomus japonicus ♦ n.d. 3 C Systellaspis debilis 0.4 11.0 1 C Hymenodora frontalis 2.5 9.1 4 C Hymenodora glacialis 1.3 13.7 5 B Hymenodora gracilis 2.1 8.4 5 C Parapasiphae sulcatifrons 0.8 19.0 4 C Parapandalus richardi 6.3 9.1 1 n.d. ♦ = relative abundance < 0.355; n.d.= not determined meso- and bathypelagicaspecies. To explain this (Brlnton, 1962), and four go.iostomatid species pattern, there seem to be two possibilities, eg. of the genus Cyclothone (Badcock & Merrett, eggs float to the upper layers of their vertical 1976). range before hatching, or hatching occurs in the Type C includes both diel vertical migrant, such deep layer and larvae move to the upper layers. es Oplophorus spinosus, end non- or slight Although movement of eggs or larvae towards diel migrant such ss Bentheogennema shallow layers has not been confirmed in the borealis^ig. 2). These species increase their present study, we consider the species such es range of vertical distribution with increasing Hymenodora glacialis Wich perform non- or body size and presumably locomotive power. limited diel vertical migrations have this pattern Notostomus japonicus is tentatively (Fig. 2). Vinogradov ( 1968) reported this type of included in typee (Fig. 2), but questions about its ontogenetic vertical migration In Hymenodora growth need Io be resolved to define its life frontalis and H glacialis in the Kurile- history. Although Krygier & Pearcy (1981) Kamchatka Trench. A similar pattern of migration reported the presence of an intermediate size Is shown in a number of other pelagic organisms class, 24-29mm CL from off the Oregon cœst, the such as the euphausiids, Thysanopoda egregia present size frequency histogram shows only two -175- Fig. 2 Vertical distribution and size frequency histograms of five pelagic shrimp species at station B. Broken horizontal bar - daytime distribution, solid bar - night distribution. 1. Sergestes armatus (ontogenetic migration type A); 2. Hymenodora glacialis (type B); 3. Bentheogennema borealis (typee), 4. Notostomus japonicus (typee); 5. Acanthephyra Quadrispinosa (typeO). classes, i.e. immatures of 5- 10mm CL and adults occurrence. of >40mm CL, with a large separation between In general, the size frequency histogram of epi- them. This suggests that the former class is able and upper mesopelagic species consists of one to to grow to the latter size within one year, which two clear modes, indicating that their spawning is much faster thon the generally accepted and/or hatching is seasonal, growth i3 rapid, and estimates of growth rates for mesopelagic and life span is comparatively short. In contrast the bathypelagic species ( see Mauchline, 1972). size frequency distribution of lower meso- and Type D is represented by Acanthephyra bathypelagic species is often composed of a quadrispinosa (Fig. 2). This species spawns number of unclear modes. This phenomenon can be from April to November, hatches from December explained by the trend in the less variable to May, and grows to 6mm CL within one year and environment for reproduction to occur whenever to 15-18mm CL (adults) within two years of age circumstances become favourable, growth is slow, (Aizawa, 1974). The specimens in the preænt and longevity considerable. sample are mainly of one year class. Because The present four types must be the only 0-yeer class are less than 5mm CL, the range of examples among many more different ontogenetic their vertical distribution could not be clarified. migration patterns. In fact, some species of the Oplophoridae produce relatively few large yolky eggs and others carry a large number of small CONCLUSION eggs (Omori, 1974), and es in the case of the type C, both diel and non-diel migrants are dealt with The present analysis indicates no apparent in the same group. Even in the bathypelagic association between diel migration pattern and life species in the type B, some may spend the larval history/ontogenetic migration pattern. It means stage In the epipelagic zone but others may stay in that, although many species have broadly the meso- or bathypelagic zone. These species overlapping depth ranges, each has a different having different life strategies and behaviour adaptation and biological strategy in relation to would have been different in ontogenetic patterns depth distribution. Within depths of co which need to be defined ss more data become occurrence of species, the difference of size available. between species is considerable, suggesting that Larval vertical distribution may be determined differences In feeding habits and seasonal by the pattern of depth distribution and migration variations in abundance permit their co of the adults; by the type of embryonic -176- development; end by the relative amount of yolk -OMORI, M.. 1974. The biology of the pelagic scrimps present in the embryo at the time of hatching in the ocean. Adv. mar. Biol., 12 . 233-342. (Ziemann, 1975). Further studies are needed on -OMORI. M. 8. 0. GLUCK, 1979. Life history end the vertical distribution of eggs and larvae, and vertical migration of the pelagic shrimp Sergestes hence, more detailed taxonomic studies of similis o(T the Southern California coast. Uii,. Bull., 77: 183-198. developmental stages are necessary. -VINOGRADOVI. E., 1968. Vertical distribution Clarification of the ontogenetic migration of the oceanic zooplankton. Puhi. House 'Nauka* patterns will allow determination of it3 biological Moscow : 320 pp.(in Russian). meaning and function, and therefore, of the -ZIEMANN, D. A., 1975. Patterns of vertical relationship between physical process and pelagic distribution, vertical migration and biogeography and of evolutionary relationship reproduction in the Hawaiian mesopelagic between food competition/predation and onto shrimp of the family Oplophoridae. Ph.D. genetic migration. thesis, Univ. Hawaii : 112 pp. REFERENCES -AIZAWA, Y., 1974. Ecological studies of mlcro- nektonic shrimps in the western North Pacific. Bull. Ocean Pes. Inst., Univ. Tokyo, 6 : 1-84. -ANONYMOUS. 1980. Biological sampling: On the Kaiyo-Maru type opening-closing midwater nel (KOC net). Survey report on marine biota and background in connection with ocean dumping of low-level radioactive wastes (1977 1980). R.V. Kaiyo-Maru, Fish. Agency Japan : 23pp. (in Japanese) -BADCOCK, J. & N. R. MERRETT, 1976. Midwater fishes in the eastern North Atlantic I. Vertical distribution and associated biology in 30’N, 23* W, with developmental notes on certain myctophids. Prog. Oceenogr., 7: 3-58. -BRINTON. E.. 1962. The distribution of Pacific euphausiids. Bull. Scripps Inst. Oceenogr., 6 : 51-270. -KIKUCHI, T. & M. OMORI. 1985. Vertical distribution and migration of oceanic shrimps at two locations off the Pacific coast of Japan. Deep-Sea Pes., 32 . 837-852. -KRYGIER, E E. & W. G. PEARCY, 1981. Vertical distribution and biology of pelagic decapod crustaceans off Oregon. J. Crust. Bio!., t : 70-95. -MAUCHLINE, J., 1972. The biology of bathypelagic organisms, especially Crustacea. Deep-Sea Pes., Î9. 753-780. -OMORI, M.. 1967. Calanus cristatus and sub mergence of the Oyashio water. Deep-Sea Pes., Id: 523-532. -OMORI. M.. 1969. The biology of a sergestid shrimp Sergestes lucens Hansen. Bull. Ocean Pes. Inst. Univ. Tokyo, d: 1-83. -177- IMPORTANCE OF VERTICAL DISTRIBUTION STUDIES IN BI06E0GRAPHIC UNDERSTANDING : EASTERN TROPICAL PACIFIC VS. NORTH PACIFIC CENTRAL GYRE ICHTHYOPLANKTON ASSEMBLAGES VALERIE J. LOEB Moss Landing Marine Laboratories, U.S.A. INTRODUCTION RESULTS Biogeographic studies of mesopelagic fishes Doubled estimated abundance and lower diversity traditionally have been based on distributions of of ETP vs CO ichthyoplankton (Table I) can be juvenile and adult stages relative to large scale related to overall higher primary productivity hydrographic and biological features (eg., water and hydrographic complexity and variability of masses and productivity levels). Enhanced the ETP ecosystem relative to the CO. Despite understanding of factors possibly affecting the similar mixed layer temperatures and depths (ca. composition end structure of fish assemblages 26*C, 40m) the assemblages had significantly within different zoogeographic regions might different (Kolmogorov-Smirnov test, P<0.0l) result from an examination of both larval and vertical distribution patterns (Fig. I): 7051 of adult stages relative to finer scale distributions of 0-100m CO larvae occurred within the upper physical and biological conditions. As an example 50m (mixed layer), while 665? of ETP larvae are the results of a comparative stud/ of 0-100m were below this layer. ichthyoplankton assemblages sampled by The overall depth distribution differences of replicated 25m depth stratified bongo tows at ETP and CO larvae have associated species 28*N I55*W in the North Pacific central g/re composition differences. Qonostomatids and (CO) and near I3*N and 130*W in the Eastern myrophitis contributed >905? of total larvae in Tropical Pacific (ETP) during late summer (Loeb the two areas, however, both families had & Nichols, 1984). significantly deeper distributions in the ETP than Table I. Comparisons of ichthyoplankton collected in nighttime stratified bongo samples in the North Pacific central gyre and eastern tropical Pacific during late summer. Mixed layer temperature (ca. 26*0 and depth (ca. 40m) was similar in both cases. CENTRAL GYRE EASTERN TROPICAL PACIFIC DEPTH MEAN NO. NO. NO. MEAN NO. NO. NO. INTERVAL IOOOm-3 TAXA SAMPLES 1000m-3 TAXA SAMPLES 0-25m 312 41 (IO) 242 28 (15) 25-50m 676 60 (IO) 642 32 (13) 50-75m 254 49 (IO) 1034 35 (14) 75-100m 166 50 (IO) 777 38 (14) TOTAL 1408 83 (40) 2695 56 (56) -170- ABUNDANCE * '.M't '.tit * * IMS Iii.) DEPTH TOTAL LARVAE mixed layer 0 25 SO 75% 0 75 50 75% 50 - mixed Jayer Fig. 2 Nighttime vertical distribution profiles for major ichthyoplankton components in the 100 - North Pacific central gyre and Eastern Tropical Pacific during late summer. Distributions are based on percentage of total 0-100m abundance Fig. 1 Nighttime vertical distribution profiles present within each of four 25m depth intervals for ichthyoplankton in the North Pacific central and are presented for (a) total gonostomatids gyre (CG) and Eastern Tropical Pacific (ETP) (dotted line) and numerically dominant during late summer. Distribuions represented as gonostomatids species and (b) total myctophids percentage of total 0-1 OOm abundance present (dotted line) and myctophid subfamilies within each of four 25m depth intervals. Lampanyctinae and Myctophinae. CO (Fig. 2;Kolmogorov-Smirnovte3ts,P Subfamily Myctophinae Subfamily Myctophinae Diogenichthys laternatus Benthosema suborbitale Gonichthys tenuiculus D/ogenuhthus atlanticus Hygophum atratum Hygophum proximum I Hygophum proximum Hygophum reinhardti ----- 1 Myctophum surda! n natum Myctophum nitidulum l Myctophum asperum I Symbolophorus evermanni r 1 I Myctophum nitidulum larvae | ~1 edulis ^60! lervilebumfanceE^ Symbolophorus evermanni lervae f ‘ adults > AOI larval abundance ES3 Fig. 4 Larval (upper bar) and adult (lower bar) nighttime depth distributions for the more Fig. 3 Larval (upper bar) and juvenile and adult abundant lampanyctine and myctophine (lower bar) nighttime depth distributions for the (Myctophidae) species taken in the eastern more abundant lampanyctine and myctophine tropical Pacific during late summer. Hatched (Myctophidae) species taken in the North Pacific larval depth range indicates depth intervals where central gyre during late summer. Hatched larval >80* of estimated 0- 100m abundance occurred. depth range indicates depth intervals where >90* Dashed lines for both larvae and adults Indicate of the estimated 0-600m water column abundance probably deeper distributions. Adult depth occurred. Adult depth distributions from Clarke distributions from Robison ( 1973) and Wisner (1973). (1976). -150- larval and adult stages. In the F.TP large macrozooplankton biomass (Timonin & Voronina, mocrozooplankton concentrations occur both day 1977; Parin, 1977); 2. decreasing vertical and night within the mixed layer and often at the migration activity by net- and macro-zooplankton surface in conjuction with high primary and mesopelagic fishes (Timonin & Voronina, productivity rotes; macrozooplankton abundance 1977; Parin, 1977); 3. increasing myctophid is relatively low at depths >!50m (Longhurst, species diversity due to increasing numbers of 1976). These concentrations could directly affect nonmigrating lampanyctine species (Parin, the adult assemblage by providing a selective 1977); end 4. increasing proportions of total ^Vantage to predatory species migrating into (0-250m) larval fishes occurring in the mixed surface layers to feed and could affect larval layer relative to thermocline and deeper waters distributions through increased competition for (Gorbunova, 1977). food and/or predation relative to deeper areas. Nocturnal predatory activities of the migratory adults could aiso provide a selective advantage for CONCLUDINO REMARKS deeper living larval stages. In contrast, overall low water column productivity and more evenly These comparative studies indicate the value of distributed macrozooplankton biomass through the vertical distribution information for both larval upper 600m of the CO (McGowan & Walker, and adult stages in understanding geographic 1979) probably offer a selective advantage to differences in the composition of mesopelagic fish moderate or low energy migrators and non assemblages. They aiso indicate the necessity of migrating species with larvae in the lower mixed coincidental Information on the vertical layer below depths of modestly increased night distributions of other biological and physical zooplankton biomass and above adult predatory parameters and similarity or standardization of activities. sampling techniques to permit Interregional comparisons of data sets. At present there 8re few oceanic ichthyo DISCUSSION plankton assemblage studies on which to base ecosystem comparisons. This is in part due to past These observations on larval and adult fish species identification problems, but recent vertical distributions and species compositions advances in larval fish texonomy (Blaxter, relative to overall values and vertical 1984) have greatly reduced this problem. distribution of primary productivity 8re Similarly, there have been few multidisciplinary supported by the results of multidisciplinary studies relating adult and larval fish vertical studies made across the eastern equatorial Pacific distributions to other biological and physical (97*W to 155*W) by Soviet scientists during parameters. This is attributed to the lack of Cruise 17 of the R/V "Akademik Kurchatov". adequate and reliable depth stratified sampling Sorokin et al. (1977) reported highest primary devices. Development of the Manta neu3ton net hss productivity rotes in the eest (97*W) with made possible quantitative sampling of the at maximum chlorophyll concentrations, phyto times very important surface layer. Additionally, plankton biomass and photosynthesis rates within recent development of electronically controlled the shallow mixed layer and upper thermocline. net systems such as MOCNESS end BIONESS Progressing westward, the mixed layer deepened, (Wiebeetal., 1976; Sameoto et al., 1980) have nutrient levels and primary productivity values resolved problems of taking replicated decreased, end chlorophyll and phytoplankton quantitative samples at known and controllable biomass values became more evenly distributed depths intervals. Attached environmental sensing through the upper water column (O-IOOm). systems permit simultaneous collection of Associated with east to west changes in primary important physical data. Additional attached productivity were: t. decreasing, deepening and devices (e.g., photometers, acoustics sounders, more evenly distributed values of net- and particle counters, fluormetera, and net releeæ -101- triggered niskin bottles) will allow quantitative -SAMEOTO, 0. D.. L. 0. JAROSZYNSKI 6. W. B. description of other environmentally important FRASER, 1980. BIONESS, a new design in multiple net factors associated with net catches. With these net zooplankton samplers. Dan. J. Fish. Aquat. Sei., systems we have the ability to adjust vertical 37: 722-724. sampling intervals to biologically important -SOROKIN, Yu. I.. I. N. SUKHANOVA, G. V. KONOVALOVA & E. B. PAVELYEVA, 1977. Primary parameters (eg., mixed layer and thermocline production and the phytoplankton of the equatorial depth, chlorophyll maxima, isolumes etc.) based region in the eastern Pacific Ocean. Pot. Arch. on real-time shipboard displays rather thBn Hydrobioi., 2d{suppl.): 145-162. relying on fixed and arbitrary sampling intervals -TIMONIN. A. G. & N. M. VORONINA. 1977. Net which often overlap and obscure their plankton distribution along the equator in the eastern significance. The largest problem now facing such Pacific Ocean. Pot. Arch. Hydrobioi., 2d descriptive biological oceanography/pelagic (suppl.): 281-305. biogeography studies is obtaining necessary WIEBE, P. H., K. H. GURT, S. H. BOYD & A. W. funding MORTON, 1976. A multiple opening/closing net and environmental sensing system for sampling zooplankton. J. mar. Pes., 3d: 313-326. REFERENCES -WISNER, R. L., 1976. The taxonomy and distribution of lanternfishes (Family Myctophidae) of the eastern Pacific Ocean. U.S. Navy Ocean Pes. Deve/opm. "BLAXTER, J. H. S., 1984. Ontogeny, systemalics Act. Pep., 3: 229 pp. and fisheries. In: H. 0. Moser (ed.). Ontogeny and systemalics of fishes. Special Puhi. 1. Am. Soc. lchthyol. Herpetol. : 1-6. -CLARKE, T. A.. 1973. Some aspects of the ecology of lanlernfishes (Myctophidae) in the Pacific Ocean near Hawaii. Fish. Butt., U.S. 7/ : 401-434. -GORBUNOVA, N. N„ 1977. Vertical distribution of the fish larvae in the eastern equatorial Pacific Ocean. Pot. Arch. Hydrobioi., 2d{ suppl.): 371-386. -LOEB, V. J., I960. Vertical distribution and development of larval fishes in the North Pacific central gyre during summer. Fish. Bi/H. (U.S.), 77. 777-793. -LOEB, V. J. & J. A. NICHOLS, 1984. Vertical distribution and composition of ichthyoplankton and invertebrate zooplankton assemblages in the eastern tropical Pacific. Biot. Pesq., fj : 39-66. -LONGHURST, A. R, 1976. Interactions between zooplankton and phytoplankton profiles in the eastern tropical Pacific Ocean. Deep-Sea Pes.. 23 : 729-754. -MCGOWAN. J. A. k P. W. WALKER. 1979. Structure in the copepod community of the North Pacific Central Gyre. Seoi. Fionogr., VP: 195-226. -PARIN, N. V.. 1977. Changes of pelagic ichthyocoenoses along the equator in the Pacific Ocean between 97’ and 155*W. Pot. Arch. Hydrobioi., 2d( suppl.): 387-410. -ROBISON. B. H , 1973. Distribution and ecology of midwater fishes of the eastern North Pacific Ocean. PhD. thesis, Stanford University. 175 pp. -182- GENETICS, LIFE HISTORIES, AND PELAGIC BIOGEOGRAPHY NANCY H. MARCUS Woods Hole Oceanographic Institution, U.S.A. INTRODUCTION mental factors (eg. temperature, salinity, food quantity and quality) on biological traits (e.g. Biogeography is the study of the distribution and growth, development, reproduction, life span, abundance of organisms. Studies of ancient excretion, respiration and feeding) (Dagg, 1978; patterns revealed through analyses of the fossil Vidal & Whitledge, 1982; and many others). Very record provide insight into present day patterns few studies have addressed the relative of higher taxa (e.g. families). Contemporary importance of genetic factors in regulating the distributions at the species level can be used to population dynamics of holoplanktonic taxa. provide insight into evolutionary processes and the mechanisms of spéciation in the sea. Present day patterns of distribution and DISCUSSION abundance of species represent the outcome of interactions between intrinsic and extrinsic The two major approaches used to gain insight into factors. The intrinsic component lies in the the genetics of marine species have been genetic structure of the species, and reflects electrophoresis and quantitative genetics. adaptation to the current environment, as well as Electrophoretic analyses of enzymes h8ve the genetic constitution of the species' ancestors. provided insight into the population genetics of a Extrinsic factors include physical and chemical variety of marine organisms including features of the environment such es temperature echinoderms, crustaceans, polychaetes, molluscs, and salinity, and biological features such as coelenterates, and fish. Reviews by Burton competitors and predators. The distribution and ( 1983), Koehn ( 1984), and Nelson & Hedgecock abundance of a species is not a static property The ( 1980) provide excellent summaries of the work changes that occur reflect variation in the on invertebrates. The majority of these studies intrinsic and extrinsic factors. however, deal with benthic animals that have a The aim of this paper is to emphasize the meroplanktonic larval stage. Relatively few importance and connections between the genetics, studies have involved holoplanktonic organisms. A life histories, and biogeography of marine weakness of electrophoresis is thai the adaptive holoplanktonic organisms. I have chosen to limit significance of the different electromorphs ( i.e. my discussion here to the group that I am most mobility variants) is seldom known, so that their familiar with, namely the copepods. Whenever importance in the evolutionary process and possible I will extend my arguments to include spéciation is difficult to assess. Moreover, the other qroups as well. Most studies which deal with relevance of different electromorphs to population the population dynamics of marine planktonic growth is not clear. copepods involve the examination of only a small A few studies have addressed these problems in spatial or temporal subset of the species. The recent years. For example, biochemical studies extent to which such data are representative of the have shown that the functional properties of whole species is rarely considered. Such research allozyme variants are different (Hoffman, 1981 h8S primarily involved cohort analyses of field for Metridium senile a sea anemone; Burton & populations (Colebrook, 1982; Landry, 1978, Feldman, 1983 for Tigriopus californicus an Corkett & McLaren, 1970; and many others), and harpactlcoid copepod; Hllbish& Koehn, 1985 for laboratory studies of the influence of environ Mytilus edulis a bivalve). Moreover, for -103 Tigriopus (Burton & Feldman, 1983) and varying selection pressures, coupled with short Mytilus {Hilbish et al., 1982) respectively, it generation times, since the abundance of many h8s been demonstrated that allozyme variants of marine zooplankters fluctuates seasonally, and glutamate-pyruvate transaminase and amino- many species have very extensive geographic peptidase-1 differentially affect cell volume and distributions. thus tolerance to osmotic stress via the regulation To dete genetic studies have led to the of intracellular amino acid concentrations. Other formulation of severol general concepts concern evidence relevant to this problem comes from the ing the maintenance of genetic variability, and apparent relationship between heterozygosity and how species cope with environmental hetero growth rates in oysters (Koehn & Shumway, geneity on temporal and spatial scales (see 1982) and mussels (Koehn & Gaffr.ey, 1984). references in Battaglia & Beerdmore, 1978; Although it has been argued that the high growth Nelson & Hedgecock, 1980). In regard to the rates ere due to the increased metabolic efficiency pelagic marine environment theory predicts that of heterozygotes, the mechanism underlying the the genetic variability of neritic species should relationship has not yet been clarified. generally be low whereas the genetic variability Quantitative genetics is designed to show levels of oceanic species should be high. The predicted of heritable variation for traits related to difference is attributed primarily to the greater population growth i.e. fecundity, development instability of coastal waters due to waves, time, mortality, age at maturity, life span, body currents, tides and seasonal changes. By size (Falconer, 1981). This Is an approach that maintaining only a few broadly functioning alleles has been used for decades by breeders of it has been proposed that species are better able to domesticated plants and animals. It provides an cope with such environmental variability. Within estimate of the herltablltty of a trait, which is the regions the different life history patterns of ratio of the additive genetic variance to the total species probably contributes to different levels of phenotypic variance for the trait. Knowledge of genetic variability. For example in temperate the heritability of a trait can be useful in coastal waters which undergo marked seasonal predicting the response of the trait to selection, variation some species may respond to the and thus the potential for evolutionary change. The temporally changing environmental conditions rate of change may, however, be subject to with long lived individuals that are able to constraints relating to pleiotropy, linkage, and tolerate the changes with a few broadly environmental interactions (Falconer, 1981). functioning alleles. Other species with short Since this approach requires the breeding of generation times and high genetic variability individuals under controlled conditions, relatively might respond with different individuals (i.e. few marine species have been analyzed. Most genetic combinations) favoured in each studies have involved small crustaceans with generation. Thus, short lived copepods such es relatively short life spans, and mollusc species Acartia spp. which undergo several generations that are important in aquaculture. Studies by during one year should be more variable than McLaren, Corkett, and Bradley and colleagues on longer lived species such es Calanus spp. marine planktonic copepods indicate the existence It h8s long been recognized that many marine of large amounts of heritable variation for traits planktonic organisms have very broad spatial that are closely related to population dynamics distributions which often encompass an extensive (e.g. body size, physiological tolerance, age at horizontal and vertical gradient (see Van der maturity) (see review Bradley 1982; McLaren, Spoel & Pierrot-Bults, 1979). Broad horizontal 1976; Marcus, 1985). The maintenance of high distributions have largely been attributed to their levels of genetic variation suggests that selection potential for dispersal across great distances in may assume an important role in determining the ocean currents. Despite evidence of phenotypic expression of these traits under natural differences in morphological, physiological, and/ conditions. The maintenance of high levels of or behavioral traits between populations from variation could be due to temporally or spatially distant areas, it was initially believed that -184- holoplanktonic species were genetically homo eventually reflected at the higher levels of geneous due to the potential for considerable organization. panmixis. Consequently, the observed phenotypic differences were often ascribed to environmental modification, and phenotypic plasticity The REFERENCES results of several studies on benthic in vertebrates with long lived planktonic larval -ANDERSON, W., 1983. Achieving synthesis in stages (recent review by Burton, 1983) and a population biology. In: C. King & P. Oawson (eds). few studies of pelagic copepods and euphausids Population Biology: Retrospect and (see references cited above; Marcus, 1984, Prospect. Columbia Univ. Press, Now York : 1985; Bucklin & Marcus, 1984; Fevolden, 189-204. -BATTAGLIA. B. & J. BEARDMORE (eds), 1978. 1984) indicate that this assumption is not valid; Marine Organisms: Genetics, Ecology and temporal and spatial genetic variability have been Evolution. Plenum Press, New York: 757 pp. documented in these groups. Further work is -BRADLEY, B., 1982. Models for physiological and necessary to quantify and establish the genetic adaptation Io variable environments. In: H. significance of this variation. Dingle & J. Hegmann (eds). Evolution and Genetics of Life Histories. Springer Verlag, New York : 33-50. CONCLUSIONS -BUCKLIN, A. 6, N. MARCUS. 1984. Genetic different iation of populations of the planktonic copepod, Revealing the genetic basis of this phenotypic Labidocera aestiva . Mar. Biot., 8d\ 219-224. variation is necessary to understand the -BURTON, R„ 1983. Protein polymorphisms and mechanlsm(s) which enable species to adjust to genetic differentiation of marine invertebrate populations. Mar. Bio/. Lett., d: 193-206. environmental change, the potential importance of -BURTON, R. 8, M. FELDMAN, 1983. Physiological emigration in the re-population of foreign areas, effects of an allozyme polymorphism: Glutamate- and the evolutionary steps that are basic to pyruvate transaminase and response Io hyperosmotic spéciation. Genetic studies ire of fundamental stress in the copepod, Tigriopus californicus. importance to biogeography. There are many Biochem. Genei., 2/ : 239-251. problems that need to be addressed. These include: -COLEBROOK, J., 1982. Continuous plankton records: 1. the relationship of life history, population persistence in time series and the population dynamics structure, and genetics to spéciation; of Pseudocalanus elongatus and Acartia clausi. Mar. 2. the relationship of dispersal and genetic Bio/., 66: 289-294. structure of species; -CORKETT, C. & I. MCLAREN. 1978. The biology of 3. the relative importance of population size Pseudocalanus. Adv. mar. Biot.. 15: 1-231. (drift) and selection in effecting evolutionary -DAGG, M., 1976. Estimated in situ rales of egg production for the copepod, Centropages typicus change; (Kroyer) in the New York Bight. J. exp. mar. Bio/. 4. the functional properties of different allele Eco/., Jd: 183-196. products; -FALCONER, D„ 1981. Introduction to 5. the relationship between genetics and Quantitative Genetics. Longman, London: 340 pp. bioenergetics to determine whether genotypes are -fEVOLDEN, S., 1984. Biotic and physical environ differentially adapted to food regimens. mental impact on genetic variation of krill. Crust. Although genetics probably plays only a small Bio!., d : 206-223. role in directly determining changes at higher -HILBiSH. T.. L. DEATON & R. KOEHN, 1982. Effect of levels of organization (e.g. communities and an allozyme polymorphism on regulation of cell ecosystems), it assumes an important role at the volume. Nature, 29B : 688-689. level of populations (Anderson, 1983). Short -HILBISH, T. & R. KOEHN. 1985. Dominance in term changes are recognized as adaptation; physiological phenotypes and fitness at an enzyme locus. Science, 229 \52-54. long-term changes appear as evolution and are -HOFFMAN. R.. 1981. Evolutionary genetics of -185- Metridium senile. Kinetic differences in phospho- glucose isomorase allozymes. Biochem. genei., 19. 129-144. -KOEHN, R„ 1984. Ute application of genetics to problems in the marine environment: future areas of research. NERC, Swindon : 1-11. -KOEHN, R. & P. GAFFNEY. 1984. Genetic hetero zygosity and growth rate in Mytilus edulis Mar. Biol., 32: 1-7. -KOEHN, R. & C. SHUMWAY, 1982. A genetic/physiological explanation for differential growth rale among individuals of the american oyster, Crassostrea virginica (Gmelin). Mar. Biol. Lett., J: 35-42. -LANDRY, M„ 1978. Population dynamics and production of a planktonic marine copepod, Acartia clausi, in a small temporate lagoon on San Juan Island, Washington. Int. Rev. ges. Hydrob., 63 : 77-119. -MARCUS. N.. 1984. Variation in the diapause response of Labidocera aestiva (Copepoda: Calanoida) from different latitudes and its importance in the evolutionary process. Biol. Bull., 166 :127-139. -MARCUS, N.. 1985. Population dynamics of marine copepods: The importance of genetic variation. Bull. mar.Sei., 37. 684-690. - MCLAREN, N., 1976. Inheritance of demographic and production parameters in the marine copepod, Eurytemora herdmani. Biol. Bull., 151: 200-213. -NELSON. K. & D. HEDGECOCK, 1980. Enzyme polymorphism and adaptive strategy in the decapod Crustacea. Am. Nat., ! 16 : 238-280. - VAN OER SPOEL, S. & A. C. PIERROT-BULTS (eds), 1979. Zoogeography and Diversity of Plankton. John Wiley and Sons, New York: 410 pp. -VIDAL, J. U T. WHITLEOGE, 1982. Rates or metabolism of planktonic crustaceans as related to body weight and temperature of habitat. J. Pianii. Pes., J: 77-84. -186- WHAT CONSTITUTES AN OPEN-OCEAN POPULATION? JOHN MAUCHLINE D unstaff nage Marine Research Laboratory, UK. INTRODUCTION areas (Baker etal., 1973; Rœet al., 1980). The nets were fished open to depths between 2000 and AngeK 1977), In assessing limitations to the 2600m where they were towed horizontally for measurement of ecological parameters in the four hours. This horizontal fishing transect is mesopelegic environment, concludes: Thus in deeper than the bathymetric distributions of the ecological studies for which long time series are euphausliids and mesopelagic fish discussed here. required, there may be insuperable temporal The hauls, therefore, provide oblique samples of limits to processes that can be observed in situ. these organisms. Samples were collected at two There have, however, been a number of successful monthly intervals between July, 1973 and demographic studies made using samples taken in March, 1974 and between March, 1975 and time series. The growth rates of Sergestes February, 1976 close to 55*N 12*W (Mauchline similis and Euphausia pacifica have been & Kawaguchi, 1982) Supplementary samples determined off Oregon and Southern California were collected throughout the rest of the Trough (Pearcy & Forss, 1969; Smiles & Pearcy, and on the Scottish continental shelf and the 1971; Brinton, 1976; Omori & Gluck, 1979). Rockall Bank. Oenthe ( 1969) aiso obtained a valid time series of samples of S.similis but from the. more prescribed Santa Barbara Basin, 8s did Omori et RESULTS al. (1973) of S. lucens within Suruga Bey, Japan. Comparable studies of fish included those Body length-frequency histograms for the on the myctophid Benthosema glaciale by euphausiid Thysanopoda acutifrons and the Halliday ( 1970) to the south of Nova Scotia end myctophid Benthosema glaciale are 3hown in by Kawaguchi & Mauchline ( 1982) in the Rockall figure I. Two time series of samples are re Trough in the North East Atlantic. presented in each species. Coherent histograms Thus time series of samples extending over a extend for four months, July to November, 1973 year or longer and resulting in meaningful in both species. There is evidence of coherence in demographic analyses can be obtained in some T.acuti frons from March 1975 to February, oceanic regions, at least in the proximity of 1976, a period of 11 months. In Benthosema continental slopes. This paper examines sample glaciale the histograms of July to November, time series from one such slope region, the 1975 are coherent but that of February 1976 is Rockall Trough in the northeastern Atlantic, and different. discusses some potential implications in Similar histograms hsve been obtained for biogeography. Lampanyctus macdonaldi and Proto myctophum arcticum by Kawaguchi & Mauchline (1982) and for Maurolicus THE TIME SERIES OF SAMPLES muelleri and aiso for the euphausiids Meganyctiphanes norvegica, Thysanoessa Samples were collected by Combination longicaudata, Nematoscelis megalops, Rectangular Midwater Trawls l+7m2 mouth Nematobrachion boopis and Stylocheiron Fig. 1 Length/frequency histograms from time series of samples from the Rockall Trough of the euphausiiu Thysanopoda acutifrons and the myctophid Benthosema glaciale. Those of B.glaciale after Kawaguchi & Mauchline ( 1982). Juvenile and female euphausiids above the line, males below the line. -1B7- -100- maxfmum. Histograms of Euphausia krohni Trough over periods of six or more months. and Stylocheiron longicorne, although Are there hydrographic features within the frequently presenting clearly defined modes, are Rockall Trough that can confer a residence time on irregular and defy interpretation. a group of organisms of a species such that they Plotting of the numbers of individuals of can form a population? There is a general Thysanopoda acutifrons and Benthosema northeastward drift through the centre of the glaciale occurring in the oblique hauls produces Trough (Fig. 3) at a velocity of 2 to 5cm sec"1 curves that correspond with regular seasonal (Booth & Ellett, 1983). A passively carried changes in population numbers expected from the organism would therefore require 2.5 to 6 months seasonal periods of breeding ( Fig. 2). to travel from the proximity of 54*N to the Anton Dohrn Seamount. There are opposing slope currents extending to depths of 700m on either DISCUSSION side of the drift (Booth & Ellett, 1983). The currents are some 10km in width and have Modes can be followed through the time series of velocities of 16 —5cm sec-1. Mixing takes place samples of euphausiids and fish. The regularity of seasonal changes in numbers of individuals 15° 10°W correspond with seasonal periods of reproduction and lack of reproduction. Such features in time series samples infer that the same populations of the species are being repetitively sampled. This repetitive sampling seems io be effective in the N Fig. 3 Present concepts of the hydrography of the upper 700m of the Rockall Trough. The directions of the slope currents on the esst and west sides and that of the general north-eastward drift are shown. Arrows on the slope currents indicate mixing and those on the deep-water side of the currents Inu. '*3 possible shedding of eddies. The Fig. 2 Seasonal changes in the mean numbers of anticyclonic circulation around Anton Dohrn Thysanopoda acutifrons (dots and solid line) Seamount is over its slope and eddies are shed and Benthosema glaciale (triangles and eastwards. Hatched lines show less permanent hatched line) in samples from the Rockall Trough. features such as possible current paths ss Standard deviations are shown where three or detected by sub-surface drogues. (Booth, Ellett & more samples ara available. Meldrum, unpubl.) -169- along the edges of these currents and eddies can be individuals. Expatriate areas of oceanic species shed from them into the Trough. from the Trough are defined (Fig. 4) from the data A sub-surface droque (at 116m depth) of Einarsson (1945) Oestvcdt (1955), Dahl meandered southwards through the Trough, (1961), Fraser (1968) and Wiborg (1968). presumably in a series of eddies, against the Wiborg describes populations of oceanic species of general northeastward drift (Fig. 3) (Booth & euphausiids in Norwegian fjords that have been Meldum, 1984). There are thus mechanisms for introduced by influxes of Atlantic water. He the formation and retention of populations within considers that 'the populations are supplied from this region, certainly for periods of three to six outside at more or less regular intervals'. The months, the duration of coherence commonly found mechanism by which this will take place is shown within the histograms (Fig. 1). in figure 4. Populations of myctophids and euphausiids Backus et al. (1977) draw the easternmost aggregate, some species very strongly at certain segment of the subarctic-temperate boundary seasons. Aggregated individuals, 8S opposed to arbitrarily by using the 9*C isotherm at 200m dispersed, are more likely ali to experience the depth between 59*N, 22*W and60*N, 5‘W (Fig. same hydrographic circumstances in a mixed 4). The northern breeding limits of a number of region such as the Rockall Trough. Their species, however, appear to be south of this, expatriation could occur Irregularly but would between about 50*N and 50*N. Further, the result in movement of populations (large relatively large scale expatriation of oceanic numbers of individuals) rather than single species north and north-eastwards from the Trough to latitudes as high as 65*N and on a more or less regular basis suggests some modification of the concept of the easternmost segment of this boundary. The northeastward slope current can act as a ''pump'' to inject temperate oceanic species towards the Norwegian Sea and allow maintenance of populations outside the principal biogeographic range of the species. Oceanic species can aiso be advected in the southward slope current round the Rockall Bank and reach the Iceland and Norwegian Basins. This situation at the )80d. • easternmost segment of the subarctic-temperate boundary of Backus et al. ( 1977) reinforces the concept of plasticity in some areas of such projected boundaries. REFERENCES RkUII Trtvfh Eifilrialis -AN6EL, M. V., 1977. Windows Into a soa of confusion: sampling limitations to the measurement of ecological parameters in oceanic mid-water Fig. 4 Recognized expatriate areas of oceanic enviroments. In : N. R. Andersen & B. J. Zahuranec, species from the Rockall Trough. Routes and (eds). Ocean sound scattering prediction. Mar. travel times (days) determined by sub-surface Sei. 5. Plenum Press, New York and London : 217-248. drogues are indicated. The easternmost segment of -BACKUS, R. H.. J. E. CRADDOCK. R. L. HAEORICH the boundary between the subarctic and temperate B. H. ROBISON, 1977. Atlantic mesopelagic zoogeo faunal provinces (Backus et al. 1977) is shown graphy. Mem. Sears Fdn mar. Res.. 7 : hatched between 59*N, 20*W and 60*N, 5*W. 266-287. -190- -BAKER, A. de C.. M. R. CLARKE 8. M. J. HARRIS. -WIBORG, K. F„ 1968. Atlantic euphausiids in the 1973. The N.1.0. combination net (RMT 1+8) and fjords of western Norway. Sarsia, 33: 35-42. further developments of rectangular midwater trawls. J. mar. biol. Ass. U.K., 53 : 167-184. -BOOTH. 0. A. h. D. J. ELLETT. 1983. The Scollish continental slope current. Goni. Shelf Res., 2 : 127-146. -BOOTH. D. A. & D. T. MELDRUM, 1984. Drifting buoys in the northeast Atlantic and Norwegian Sea. ICES, CM/C 7 : 9pp. -6RINT0N, E., 1976. Population biology of Euphausia pacifica off Southern California. Fish. Bull. N.O.A.A., U.S., 7*1 : 733-762. -DAHL. E.. 1961. A record of the euphausiacean Stylocheiron longicorne from west Norway. Sarsia, 4: 39-421. -EINARSSON. H.,1945. Euphausiacea. I. North Atlantic species. Dana Rep., iV: 1-165. 4RASER, J. H., 1968. The overflow of oceanic plankton to the shelf waters of the north-east Atlantic. Sarsia, 34: 313-330. -6ENTHE, H. C.. 1969. The reproductive biology of Sergestes similis (Decapoda, Natantia). Mar. Bio!., 2: 203-217. -HALLIDAY. R. 6., 1970. Growth and vertical distribution of the glacier lantern fish, Benthosema glaciale, in the northwestern Atlantic. J. Fish. Res. Bd Can., 27: 105-116. -KAWAGUCHI, K. L J. MAUCHLINE. 1982. The biology of myctophid fishes (Family Myctophidae) in the Rockall Trough, northeastern Atlantic Ocean. Biol. Oena nog., 1: 337-373. -OMORI, M. & D. GLUCK. 1979. Life history and vertical migration of the pelagic shrimp Sergestes similis off the Southern California coast. Fish. Bul/., N.O.A.A., U.S., 77: 183-198. -OMORI, M.. T. KONAGAYA 8, K. KAZUO. 1973. History and present status of the fishery of Sergestes lucens (Penaeidae, Decapoda, Crustacea) in Suruga Bay, Japan. J. Cons. ini. Explor. Mer., 35 : 61-77. -PEARCY. W. G. & C. A. FORSS, 1969. The oceanic shrimp Sergestes similis off the Oregon coast. Limnol. Oceanogr., M: 755-765. -ROE. H. S. J.. A de C. BAKER. R. M. CARGSON, R. WILD & D. M. SHALE, 1980. Behaviour of the Institute of Oceanographic Science's Rectangular Midwaler Trawl: theoretical aspects and experimental observations. Mar. Biot., 56 : 247-259. -SMILES, M. C. & W. C. PEARCY. 1971. Size structure and growth rale of Euphausia pacifica off the Oregon Coast. Fish. Bull., N.O.A.A., U.S., 69: 79-86. -191- THE BIOGEOGRAPHY OF PELAGIC ECOSYSTEMS JOHN A. MCGOWAN Scripps Institution of Oceanography, U.S.A. INTRODUCTION McGowan, Î 963; Brodsky, 1965; Frost & Fleminger, 1968; Beklemishev, 1969; Venrlck, During the decodes 1950 to 1970 a large number 1971; Okade & Honjo, 1973; Reis et al., 1978; of wide ranging oceanographic expeditions McGowan & Walker, 1985). I have summarized explored the Pacific Ocean. These often Included these patterns in two earlier papers and so have the systematic sampling of macrozooplankton in Reid et al. ( 1978). Among other attributes, two of the upper 200m or so. The resulting collections of their features stand out; many thousands of samples provided the basis for 1 ) There is a large amount of agreement across the mapping of species patterns in the epipelagic higher taxa es to the shape of the patterns. That is, zone. Many deeper net tows were aiso Included in there are copepod species patterns that look like these collections but their sampling intensity wos those of euphausiids, pteropods or thaliaceens. A much less, so that the determination of pattern for careful statistical analysis agreed with simple deeper living organisms Is considerably less visual observations of the maps, that there is certain. Although the expeditions and cruises were significant spatial co-occurrence of species often done in different seasons and years in (Fager & McGowan, 1963). different areas, it was possible to moke composite 2) The patterns of most species assemblages maps of species abundance which included both strongly resemble those of the major positive and negative records. Both records are circulation-recirculation systems of the Pacific. essential in the mapping of any entity that does not The y. adients and major frontal zones deliniating have a continuous distribution (for example: these circulation systems were determined species vs. biom8$s) and whose abundance may be independently of those of the ranges of species influenced by environmental processes and events. assemblages and yet there is excellent It is important in the interpretation of species correspondence. pattern to know if blank areas are blank because Why should evolutionary adaptation have of lack of sampling or because an appropriate resulted in such a picture? We cannot investigate attempt to find the organism failed. Thus it Is this problem experimentally but there are critical to have a large number of samples observations that may increase our understanding. available for analysis. The expedition collections The North Pacific Subarctic cyclonic gyre and were aiso, for the most part, quantitative. This water mass; The Central North Pacific means that relative abundances can be estimated anti-cyclonic gyre and water mess; The Eastern aid gradients and smaller scale variations within Tropical Pacific, part of the great Equatorial the forger range patterns determined. Because of circulation-recirculation system of the tropical this detail it is possible to interpret the resultant Pacific (Fig. I) have been studied, es systems, maps of abundance, rarity and absence, In long enough so that their structure and function ecological terms and thus help us understand the may be compered. We can now ask how these three conditions under which oceanic populations vary. provinces differ and in what ways are they A number of researchers have, fortunately, similar? In other words what Is the empirical teken this quantitative approach end we now have evidence for the oceanic habitat characteristics a basic framework of biogeographic pattern for that are (were) important in evolution? the Pacific, that is amenable to ecological and oceanographic interpretation (Bieri, 1959; Bradshaw, 1959; Bowman, I960; AlvarifSo, 1962; Brinton, 1962; Nemoto, 1962; Fager & ■120 140 160 E180 160 140 120 100 80_____W 120 140 160 E180 160 140 120 IOP 80____ VV 192- 2 9 -1 Fig. 1 k. The Subarctic and Subontarctic Pacific faunal provinces. B: North and South Pacific Central C/re faunal provinces. C: Eastern Tropical Pacific faunal provinces, (after McGowan, 1974) Lighter shading indicates boundary zones. 193- 3 9 -1 -194- THE NORTH PACIFIC SUBARCTIC GYRE a large, seasonal change in zooplankton biomass (Miller et al., 1984). Such large scale and This is 8 cyclonic circulation system (Fig. 2) consistant structural and functional features in a with the salient feature of ali such systems; massive upward movement of deep water in its UPPER LAYER CURRENTS centre. Evidence for this process may be clearly seen In vertical sections of the eastern Subarctic where the isopleths of density, temperature, salinity and plant nutrients ali bend upward (Dodimead et al., 1963; McGowan & Williams, 1973)( Fig. 3). The salinity structure of this region differs strongly from the waters to the south. The Subarctic is a climatic region where precipitation and runoff exceeds evaporation and thus Its upper DRIFTING BUOY TRAJECTORIES layers are relatively fresh. But there is a strong tlaloci ine separating this upper layer from the lower zones (Fig. 3). Because of the excess of precipitation one might expect the upper layers would become progressively fresher. This does not occur because of the input of Heep salty water from upwelling in the centre of the system and because a large fraction of the surface waters of the southern limb of the circulation, the North L ^ , Pacific Drift, turns to the south as it nears the UPPER LAYER CURRENTS North American continent end contribute its cool, OXYGEN SATURATION AT SURFACE fresh, nutrient-rich water to the California Current. This water end its constituents are not recirculated back into the Subarctic system. The southern edge of this system is evident in figure 3 where, at about 43*N the halucline disappears. The disappearance of this characteristic feature is due to the rapid, spatial change in the climatic and hydrographic mechanisms that are responsible for its maintenance. There are very strong seasonal cycles in both hydrography and biology and this sets the region apart from others in the Pacific. This climatic seasonality results in a large annual excursion in mixed layer temperatures (about 5*C to I44C at Fig. 2 A: The gross circulation of the upper zone 504N, I45‘W). Mixed layer depths vary from of the Subarctic Pacific (after Dodomead et al., about 20m in August to about 100m (the top of 1963). B: The trajectories of satellite tracked the tlalociine) in January. At these latitudes there drifters showing the large anti-cyclonic gyre in is aiso a large excursion in the depth of light the eastern half of the central North Pacific (after penetration, out of phasa with that of the mixed McNally et al., 1983). C: The gross circulation of layer. The result Is a brief period in the spring the upper zone of the Eastern Tropical Pacific and when the critical depth exceeds the mean mixed percent oxygen saturation at the surface showing layer depth (Parsons et al., 1966); this leads to a upwelling centres (after Eastropic Atlsses vol. 2, burst of productivity and zooplankton growth and 1971 and vol. 6,1972). 195- dynamic system are obviously driven by powerful productivity, high biomass, strongly seasonal, forces of climate Interacting with the low diversity system. characteristics of the locale, such as basin shape, topography and latitude. Within the larger Subarctic system there are THE CENTRAL GYRE OF THE NORTH PACIFIC several cyclonic sub-systems (Fig. 2). Although they have not been studied 8s hss the Gulf of A ’ a The contrast between the North Pacific Central sub-system, we can assume, because of the e Gyre and Subarctic could hardly be greater of the circulation and the doming up of propo. ty CENTRAL SUBARCTIC concentrations ( Dodlmead et al., 1963). that they ANTICYCLONIC TRANSITION CYCLONIC GYRE ZONE GYRE aiso function as upwelling centres. Thus the 3600 34 bO 34 00 33 60 33 00 '2 60 Subarctic system is not a simple functional or uniform unit but consists of several similar sub-units imbedded in the larger regional system. This, within system, variability in structure may affect biological processes and aspects of pattern, for in an earlier study it W8S shown that there 34 ?0 were several loci within the Subarctic where there was a substantial abundance concordance H' N AT among the individual species populations ( Fager & McGowan, 1963). But these localized areas do not harbour unique species assemblages or endemics, and it is my quess that they are so variable in their intensity and perhaps locale that they ore too "unpredictable" to hsve served as habitats or centres for diversification where selection for specializedgenepools could proceed uninterrupted T/E ft ! 'I 'T,3i f-HOSFvATE - PHOSPHORUS SECTiQN AT i55®W for the requisite number of generations. (/j.g o’ /1 ) The Subarctic species differ greatly from others in their behaviour and life history patterns es well as morphology. The copepods have been most Fig. 3 Upper: A north-south transect of the North intensively studied and their populations hsve Pacific at I55‘W (Kodiak to Hawaii) showing been shown to hsve seasonal cycles of migratory salinity values. North of about 444N a well behaviour, reproduction and growth which are developed tlaloci i ne can be seen at iOOm. South of very closely keyed to the large scale seasonal about 38*N a shallow halocline Is present at about hydrographic processes that are so evident In this 40m. Between these two lies the "Transition Zone" area (Miller et al., 1984). Further a substantial an area of fronts, inversion and instabilities. fraction of the populations of ali of the Subarctic Arrows indicate the inferred direction of vertical plankton must "emigrate" from the system along movement, upwelling and sinking. with the southward flowing Subarctic water that Lower: The same north-south transect as above becomes part of the California Current. This loss showing the phosphate concentration. Areas of must he a important source of mortality and a upwelling in the Subarctic Gyre and vertical regular feature of the population dynamics of the mixing In the Transition Zone are Indicated by species; one to which they must have adapted. arrows. The upturned isopleths and high surface The Pacific Subarctic pelagic zone is a rich values ore consistent with the upper panel. South ecosystem in terms of annual production end of the Transition Zone, low surface nutrients and sustained high standing stocks but it is poor in downturned isopleths are consistent with the species of plankton (and probably fish and squid) expectation of generalized downwelling (after (Reid et al., 1978). That is; it is a high McGowan & Williams, 1973). -196- alt hough the two systems are contiguous. The of the gigantic Pacific Equatorial water mass. This gross circulation in the Central Gyre is may have been due to a lack of appropriate data, at anti-cyclonic and hence there is a generalized the time they wrote, or perhaps it wss felt that sinking of waters in the interior regions (Fig. 2). the continuity between the circulation of this The mixed layer temperatures are much higher region and the rest of the Equatorial zone was too than those of the Subarctic ranging from about great to warrant it being set off as a separate I8*C in winter to 24*C in summer. The mixed system with natural boundaries and distinctive in layer depths in the Central Gyre vary from a situ processes and events. However, we now know February mean of about 120m, but with broad this region does have and indigenous fauna and limits to a mid-summer mean depth of about 40m further, some species found throughout the with narrow limits. There Is a halocline In this Equatorial water mass ara absent or rare here. gyre but the more saline water is in the upper Thus populations do "recognize" it as a special layers with fresher waters underneath (Fig. 3) habitat in the same sense that they "recognize" the and there is a seasonal change in its depth. This is Pacific Subarctic and Central circulation systems. a climatic area where evaporation exceeds The region hœ some highly distinctive physical precipitation and there is virtually no runoff. The processes and hence environmental structure, nutricline is deep at well over 100m and does not that set it apart. For example; the Costa Rica dome appear to change seasonally. Most of the is a massive cyclonic gyre near 9*N 88*W caused chlorophyll in the watercolumn Is concentrated in by the reflection of the Equatorial Counter a deep (about 110m) chlorophyll maximum Current to the west (Fig. 2). Sea surface oxygen whose depth seems seasonally invariant. The saturation values are low in the centre of this primary productivity maximum Is broad but region presumably because the water has so peeks at about 50m both in winter and summer. recently welled up that it hss not yet equilibrated No seasonal changes in productivity have been with the atmosphere. Hydrographic transects detected. Both phyto- end zooplankton biomass are show the spectacular doming upward of isopleths very low and, es might be expected, there is no of ali properties (Fig. 4)(Eastropac Atlases detectable seasonality in zooplankton abundance 1970-1975). Chlorophyll and primary product (Hayward et al., 1983; Hayward & McGowan, ivity measurements show the area to be one of the 1985). most productive anywhere in the worlds tropics Biologically, the Central Gyre is highly divers. (Owen & Zeitschel, 1970). In addition to this It is the most species-rich province in the Pacific remarkable dome feature there are episodic but (Reid et al., 1978), its dominance hierarchy is apparently larga-scale, coastal upwellings in the very persistant and its community structure quite Gulfs of Panama and Tehuantepec. Thus, just 8s in stable (McGowan & Walker, 1985). The intensity the Subarctic, there are important sub-units of patchiness, on ali scales, is low (Hayward et within the system. al., 1983). There is no evidence for the type of Variations In coastal winds are responsible for within system sub-units that occur in the the episodic nature of coastal upwelling. The Subarctic. intensity of oceanic upwelling within the Costa Thus the Central Gyre is a low productivity, low Rica dome is aiso quite variable, no doubt due to biomass, non-seasonal, high diversity, relatively seasonal and Interannual changes in the strength homogeneous system. and position of the trade wind-driven equatorial circulation system. These large-scale global winds do not neccessarily co-vary in intensity THE EASTERN TROPICAL PACIFIC with local coastal winds. A third significant process, and perhaps a more consistant one, is the Although this region can be considered to hove its Input of water from the south-east; the Peru own, unique circulation scheme it was not Current's cold, nutrient rich extension along the characterized as a separate entity by Sverdrup et equator (Fig. 2). These three sources of nutrient al. ( 1942), but rather included es merely a part input may vary indepently in respons to forces -197- 88**, FEBRUARY-MARCH l%7 far shoaler in this province and with generally TEMPERATURE SALINITY OXYGEN CONCENTRATK)N imrj \) much lower oxygen concentrations than elsewhere 40 in the Pacific (Fig. 4). This peculiar regime must have had profound effects on its resident populations and has served as a strong selective force. The mixed layer depths In the Eastern Tropical Pacific have a complex topography with a series of ridges, troughs and domes. The layer ranges in 88*W. SEPTEMBER 1967 NITRATE (pg al /I) average depths from about 25m near-shore in the Oulfs of Panama and Tehuantepec to somewhat less than 80m offshore In the more oceanic regions (Bathen, 1972). The seasonal amplitude is not great ranging from about IO to 30m. The temperatures of the mixed layer range from 26 to 29'C with little seasonality but with strong spatial gradients. Production, however, varies by a factor of almost three between seasons. There is Fig. 4 Upper: The distribution of the three a broad winter-spring productivity maximum properties temperature, salinity and dissolved followed by a somewhat briefer, smaller summer oxygen in a section at 88*W through the Costa peak. This cycle is more pronounced near-shore Rica dome 8*30'N. The distribution of ali three than offshore (Owen & Zeitschel, 1970). Annual properties is consistant with the expectation of production and zooplankton biomass may be ss vigorous upwelling in this area. high os in the Subarctic Gyre (Raid at al., 1978). Lower: A north-south section from 10*S across This region seems to be only moderately rich in the equator and through the Costa Rica (tome along species but its diversity has not been well studied 88*W. The complex distribution of nutrients in and this community attribute ma/ turn out to be the entire euphotic zone is evident. The upturned as complex as is the rest of the system. The entire isopleths between 6* and 10*N are further ecosystem may aiso show large interannual evidence for a massive upwelling centre. variations since for surface layers there were strong Indications for this during the 1982-83 El Nino ( Barber & Chavez, 1983). which have different characteristic temporal scales of variation and which are themselves driven by different processes. This makes it a DISCUSSION very heterogeneous but very rich system. One of the consequences of the temporal variability in In the Pacific, a majority of the epipelagic, the rate of nutrient input is short intense but oceanic species of euphausiids, pteropoda, episodic phytoplankton blooms which "escape" heteropods and Chaetognatha strongly agree on from the control of grazers. These blooms soon range boundaries. That is, their biogeographic deplete the nutrients and the populations crash, patterns are very similar. There is strong leaving unexploited organic matter. Thus, large evidence that many additinal taxa of zooplankton, amounts of particulate detritus sink out of the phytoplankton, cephalopod, fish and marine euphotic zone and still at relatively warm mammals have many species with similar temperatures, are rapidly decomposed by patterns. While these large scale distributions micro-organisms. This results in dissolved tend to coincide, their smaller scale abundance oxygen levels sometimes close to zero at depths of variations may or may not. The biogeogrnphic 70m or less In the area of the (tome. Because of patterns cover regions of the ocean having unique this process, the entire oxygen minimum layer is hydrographic domains that are characterized by a -190- continuity of water movement; thet is they little or perhaps no effect In the Pacific circulate and recirculate; and by very different Subarctic. One could create many other plausible, climatic regimes. These circulation systems are but untested scenarios ( i.e. models) but the point large and few in number and ali trophic levels are is; these regions are not only structurally present within them. They appear to be different but aiso functionally different and the self-sustaining ecosystems. nature and timing of their respons to ordinary Why is it that evolutionary adaptation and climatic seasonality or large episodic spéciation resulted In entire species assemblages perturbations differ as well. or complete communities whose spatial We do not of course, know exactly what it is dimensions and shapes resemble the large scale about the oceanic physical environment that circulation and not the smaller scale results in the appearance or selection of environmental features? subpopulations of organisms with different Three of these circulation- or ecosystems are degrees of fitness or how these can become described here, and it should be evident from even spatially Isolated from one another and the these brief, superficial accounts of their isolation maintained so that further divers physical-chemical functional anatomy that there ification can happen. But whatever the processes are vast differences between them but are, they have apparently occurred on very large considerable continuity within them. The first scales to have resulted in the patterns we see order differences are due to the circumstances of today. That this should be so may be due to the latitude, geography, shape of the ocean basin and nature of the habitat. The ocean is stirred and global atmospheric climatic patterns. The tempo mixes, thus smaller scale physical features do not and mode of internal processes and events in these persist, as unique features, for very long regions, such as intensity of nutrient cycling and (Stommel, 1963; Haury et al., 1978). Only the recycling, are often brought about in different large scale structures have the degree of ways by different forces cr they may respond differentness and temporal persistance to allow differently to the same forces. For example; a the evolution to operate in a mobile, moving general global increase in wind speed might be medium. expected to increase the velocity and mass It seems certain thai the spatial and temporal transport of the gross surface circulation every patterns of most important ecosystem properties where. Under our present understanding this are strongly and persistently different in the would be expected to increase upwelling in the three large regions discussed. In order for these central regions of the cyclonic Subarctic Gyre. large structural differences to be maintained But this increase in rete of input of nutrient rich there must be strong functional differences as water might have little effect on productivity well. Some of these functional differences have since productivity is thought to be primarily light already been documented. Such ecosystems, along limited in this region. However, this sama with their own assemblage of well adapted species, increase In circulation would cause stronger should not be expected to respond to climatic downwelling in the anti-cyclonic Central Gyre and forcing in the same way; Indeed we already have a decrease in the upward flux of nutrients, thus some evidence that they do not. It follows, then, decreasing productivity in this already that models of pelagic ecosystem function such es oligotropha, nutrient limited regime (Eppley et those analysing the efficiency of energy transfer al., 1973). Increases in the rate of upwelling in as a means of predicting "yield" at the higher the Costa Rica dome, Gulfs of Panama and trophic levels, or those where the attempt is to Tehuantepec and thus a greatly enhanced primary determine the processes most important in productivity would result from the same general "stabilizing" the system or parts of it, must take increase In winds. Thus the esme forcing function, Into account the profound regional differences in a simple increase in global wind speeds, would structure, function and respons to climate. increase production in the Eastern Tropical Pacific, decrease it in the Central Gyre and have -199- REFERENCES -HAURY, L.R., J. A. MCGOWAN & P. H. WIEBE, 197B. Patterns and processes in the time-space scales of -AIVARINO. A., 1962. Two new Pacific Chaetognatha. plankton distributions. In: J. H. Steele (ed.) Spatial Bull. Scripps Inst. Oceanogr.. 5(1): 1-50. pattern in Plankton Communities, Plenum, N.Y. -BARBER, R. T. 8, F. P. CHAVEZ, 1983. Biological : 277-327. consequences of El Nino. Science, 222 : -HAYWARD, T. L. & J. A. MCGOWAN, 1985. Spatial 1203-1210. patterns of chlorophyll, primary production, -6ATHEN, K. H., 1972. On the seasonal changes in the macrozooplanklon biomass and physical structure in depth of the mixed layer in the North Pacific Ocean. the central North Pacific Ocean. J. Plankton Pes. 7 J. Geophys. Res. 77 . 7139-7151. (2): 147-167. -BEKLEMISHEV. E. W.. 1969. Ecology and -HAYWARD, T. L.. E. L. VENRICK 6, J. A. MCGOWAN, biogeography of the open ocean. Puhi. House 1983. Environmental heterogeneity and plankton Nauka, U.S.S.R.: 291pp.(in Russian). community structure in the central North Pacific. J. -BIERI, R.. 1959. The distribution of planktonic mar. Ros. 4/ : 711-729. Chaetognatha in the Pacific and their relationship Io -HONJO, S. Si H. OK AD A. 1974. Community structure the water masses. Limnoi Oceanogr. -/(I): 1-28. of coccolithophores in the photic layer of the -BOWMAN, T. E„ 1960. The pelagic amphipod genus mld-PacIfic. Flicropa/eonlol. 20 : 209-230. Parathemisto (Hyperiidea: Hyperiidae) in the North -MC6CWAN, J. A., 1974. The nature of oceanic Pacific and adjacent Arctic Ocean. Proc. U.S. natn. ecosystems. In: C. B. Miller (ed.) The biology of Hus.. 1/21B439). 342-392. the oceanic Pacific. Oregon Stale Univ. Press. : -BRADSHAW, J. S„ 1959. Ecology of living planktonic 9-28. Foraminifera in the north and equatorial Pacific Ocean. -MCGOWAN. J. A. &P.W. WALKER. 1985. Dominance Contr. Cushman Fdn foramin. Ros., tO (2): and diversity maintenance In an oceanic ecosystem. 25-64. Eco!, fionogr. 55(1): 103-118. -BRINTON, E., 1962. The distribution of pacific -MCGOWAN, J. A. & P. M. WILLIAMS. 1973. Oceanic euphausiids. Bull. Scripps inst. Oceanogr., ff habitat differences in the North Pacific. J. exp. (2): 51-270. mar. Biot. Eco/. 12'. 187-217. -BRODSKY, K. A.. 1965. Variability and systematic oT -MCNALLY. G. J.. W. C. PATZERT, A. D. KIRWAN, JR the species of the genus Calanus (Copepoda). 1. & A. C. VASTANO, 1983. The near-surface Calanus pacificus Brodsky, 1946 and C.sinlcus circulation of the North Pacific using satellite tracked Brodsky n. sp.. Eploraiions of the fauna of the drifting buoys. -REID, J. L., E. BRINTON, A. FLEMINGER, E. L. VENRICK & J. A. MCGOWAN, 1976. Oceanic circulation and marine life. In: H. Charnock & G. E. R. Deacon (eds), Advances in Oceanography. Plenum, N.Y.: 65-130. -STOMMEL, H.. 1963. Varieties of oceanographic experience. Science, /JP: 572-576. -SVERDRUP, H. V.. M. W. JOHNSON 6, R. H. FLEMING. 1942. The oceens: their physics, chemistry and general biology. Prentice-Hall: 1087pp. -VENRICK, E. L, 1971. Recurrent groups of diatom species in the North Pacific. Ecology, 52 (4): 614-625. -201- BIOGEOGRAPHY AND THE OCEANIC RIM : A POORLY KNOWN ZONE OF ICHTHYOFAUNAL INTERACTION N.R.MERRETT Institute of Oceanographic Sciences, U.K. INTRODUCTION the pseudoceenic group of species (sensu Hui ley, 1981), which ma/ be sub-divided into: The continental slope both truncates the -1. Obligatory pseudoceenic species, whose long- distribution of the oceanic meso- and bathypelagic slope distribution clearly parallels that of many ichthyofauna and provides the headquarters for e demersal forms, are both mesopelagic and bathy diverse assemblage of demersal fishes. Parin & pelagic fish» with affinities to either the epi- Qolovan ( 1976) discussed the peculiarity of this benthic or pelagic communities (sensu Hulley, boundary zone between the pelagic and demersal 1981) (Table I). The majority of mesopelagic Ichthyofauna. The broad congruence apparent obligatory pseudoceenic species are represent between the depths of peek abundance of oceanic atives of predominantly pelagic families (e.g. pelagic organisms and slope dwelling fishes was Sternoptychidae, Photichthyidae, Myctophidae, emphasised by Marshall & Merrett ( 1977), with Melamphaidae) whilst current evidence indicates its likely trophic significance. The slope contains that their bathypelagic counterparts tend to have a wider range of physical niches than occurs in demersal relatives (e.g. Alepocephalidae). Pelagic the open ocean, provided by the topographical members of additional demersal families, such variety of the sea-bed, together with the es Brotulataenia spp. (Cohen, 1974) & increased mixing effect of currents Impinging Thalassobathia pelagica (Cohen, 1963) upon it. Nutrient renewal resulting from such (Ophidiidae); Sciadonus spp. (Nielsen, 1969) mixing has been shown to enhance phytoplankton (Aphyonidae); Odontomacrurus murrayi, growth along the shelf break (Plngree & Merdell, Macrouroides inflaticeps and Squalogadus 1981), which in turn will affect the relative modificatus (Marshall, 1973), Mesobius productivity of the upper slope. At greeter depths, berryi and Nezumia parini (Hubbs & the increase in biomass of benthopelagic plankton Iwamoto, 1977) (Macrouridae), could possibly distributed within the I OOm stratum closest to compliment this list when further distributional the sea-bed, observed by Wlshner (1980), evidence is obtained. probably results from similar physical processes -2. Facultative pseudoceonic species are acting on sedimentary material. identifiable es a normally oceanic group whose members adopt a self-maintaining pseudoceenic distribution beyond their normal geographic ICHTHYOFAUNAL PATTERNS ASSOCIATED WITH limits. Benthosema glaciale is an example. THE SLOPE Accord1ngtoNafpakt1tlseta1.(1977) It Is the top ranking myctophid of the subpolar-temperate In broad terms much is known about the overall region of the Nordi Atlantic, yet its disjunct horizontal and vertical distributions of deep-sea distribution shows it aiso to be abundant in the pelagic fishes and their demersal relatives. Many Mauretanian upwelling ares. In examining this slope-dwellers among the latter have relatively distribution further, Badcock (1981) showed narrow bathymetric limits. They comprise en that B.glaciale has its centre of distribution assemblage which is often geographically more over the slope where it breeds end thrives. restricted and different from those of the Badcock (1981) noted five other species (viz: continental rise 8nd abyss. Such long-slope Stomies boa, Notolepis rissoi, Myctophum 'ribbon' distribution has a pelagic counterpart in punctatum, Symbolophorus veranyi and -202- Table I Examples or obligatory pseudoceanic species FAMILY SPECIES SOURCE MES0PELA6IC: tiMstmitiAw Tris/eahes hemiaei * 6rav.1964 Sternoptychidae ttM0r0ticas muelleri Hokhachova.1981 Argyrepelecas figes Badcock pars .comm. Pe/vjanus sa*. Baird. 1971 Photichthyidae Petymetme cerythaeeta • 6rey. 1964 far#//# h/achferfi • Srev.1964 Alepocephalidae Xenefermichthys capa/' " Krafft, 1985 IOS ufloubl. dela Notosedidae Sc0M0/0SM0rMs soa* Bertelsen nt al..197& Myctophidae Diaphus far masi. D. minax. Ncfpaktitis at al.,1977 D.rttei * ,D. taaningi Diaphus caerulans0 Nafpaktitis.1978 Diaphus afenemas0. D.gigas Kawaguchi 8. Shimizu. 1978 D. sagamiensis. D.subequalis. D. watasei* Diaphus fumaria 6 josae ter & Kawaguchi, 1980 L ampa fane panti fix Hulloy.1981 L amaea vctufas hectoris Hullev.1981 Zoarcidae tfatanestigma atlanticum0 Markle !■ Weanor.1979; Mai rott at al. 1986 Melamphaidae tlaiamahaes acanthemas Ebalina. 1962 BATHYPELA6IC: Alepocephalidae Bajacaiifernia megaleps ■ Krafti. 1985 Bathytrectes micre/epis * Krafft. 1985 Phetestytas pycnepteras Wisner.1977 Xenefermichthys x tpui * Nybalin, 1948; Markle & Won ear. 1979; Krafft. 1985. IOS unaubl. data Zeereidea tfaianestigma atlanticum0 Cohen ft. Pawson.1977 Parahretu/a piagiaphthaimus IOS unpubl. date * Species exhibiting seme dependence on the sea-floor. Notoscopelus bo/inDmWx similar populations which ara separated from continents by expanses in this upwelling area, apparently isolated from of oceanic floor ( i.e. the thalassobathyal zone of northerly and Mediterranean ones. Andriashev, 1977 and see Parin, 1984 end this It is noteworthy here that pseudoceanic volume); areas where enriched productivity mey distributions mary appear misleadingly complex aiso occur (cf. Isaacs&Schwartzlose, 1965). without reference to broad scale topographical More detailed examination reveals further features.Thus many such species inhabit island patterns among pelagic slope-dwelling fishes: locations and numerous rises and ridges with -1. Variation in relative density, steep slopes at bathyal depths (200-2000m) a Obligatory pseudoceanic species are often ioa num er leai dominants among pelagic slope Shimizu (1978) 'most of the slope water populations. Maurolicus muelleri Is a [ Diaphus ] species grow larger than the oceanic panoceenic example of a species frequently water species and sometimes reach 20cm or dominant In density of occurrence (Ojosaeter & more’. Indeed, D. watasei and D.coeruleus Kawaguchi, 1980)(Table II). Indeed, in upwelling attain 150-300mm and are among the largest areas obligatory pseudoceenic species may occur myctophids known (Ojosaeter & Kawaguchi, in exploitable quantities. Lampanyctodes 1980). Among the sternoptychids, the hectoris, for example, was the major component pseudoceanic Argyropsiicus gigas attains of the South African lanternfish catch of 42,560 greatest individual size (1204mm SL ); while tons during 1969- 73 ( Hulley, 1981 ). Yarella blackfordi (3004 mm SL ) end b Facultative pseudoceanic species are found in Polymetme corythaeola (2004mm SL) are increasing density in the up-slope direction. among the largest photichthyids known, as is Badcock (1981, Table 7) demonstrated an Triplophos /te/7?//7^/(350+mm SL) among the increase in density of almost two orders of gonostomatids. Conversely, none of the recognized magnitude in Benthosema glaciale among bathypelagic pseudoceanic species attain larger samples ( 0-500m depth) over the sounding range size than their oceanic congeners. 3010- 100m. c Certain oceanic species abutting the slope evidently occur in greater densities in slope RESEARCH APPROACHES regions. Notoscopelus elongatus kroeyeri, for instance, has a sub-polar temperate While endemism has been demonstrated among distribution according to Nafpaktitus et al. pelagic as well as demersal slope-dwellers, the ( 1977). It is abundant to the west of the British details of congruency of the various faunal Isles (Ojosaeter & Kawaguchi, 1980). Yet recent elements need further investigation. To facilitate preliminary investigations of the near-bottom this end, it is worthwhile considering the value ichthyofauna of the Rockall Trough in this same and limitations of the diversity of approach area of the eastern North Atlantic to the west of employed hitherto. Britain, using commercial sized midwater and demersal trawls by the Institut für Seefischerei, DIRECT APPROACHES Hamburg, showed mesopelagic densities of a Nets Ne.kroeyeri three orders of magnitude larger 1. A variety of midwater trawls have provided the over the slope than in the middle of the Trough basic information on the biogeography of (Merrettetal., 1986)( see Table II). pseudoceanic species (e.g. conical ring nets - The influence on the vertical distribution of Kawaguchi & Shimizu, 1978; Isaacs-Kidd oceanic species caused by the slope intercepting midwater trawls IKMT- Jahn & Backus, 1976; their preferred range is poorly known. Bailey Nafpaktitus et al., 1977; mouth opening/closing (1982) has indicated that blue whiting, rectangular midwater trawls (RMT 148) - Micromesistius poutassou, take up a Badcock, 1981 ; commercial-sized gear - Krefft, demersal hahit as the slope crosses their usual 1974;0jo9eeter, 1984; including information on depth of occurrence ( 300-500m). Among decapod the occurrence of benthopelagic fish far above the crustaceans, however, Hargreaves (1984) has sea-floor-Haedrich, 1974; Krefft, 1980; Stein, shown that some, but not ali, mesopelagic species 1985; I.O.S. unpubl. data). Obviously mouth may shift their vertical distribution under the opening/closing devices greatly enhance the value influence of the slope and may increase in of net collection data and their use is increasing. abundance close to the sea-floor. Bathypelagic 2. Demersal trawls have aiso contributed to the decapod crustaceans appear to be unaffected. knowledge of pseudoceanic species (e.g. Yarella -2. Maximum body size attained by mesopelagic spp., Polymetme spp. end Triplophos pseudoceenic species is often greeter than among hemingi - Grey, 1964; Scopelosaurus spp. their pelagic congeners. According to Kawaguchi & - Bertelsen etal. 1976; Diaphus coeruleus Table II Ranked abundance of the mora numerous fish species (>3X) in demersal (2006T) and pelagic (1600PT) trawl samples from Ute slope and middle of Ute Rockall Trough. SLOPE (east and west combined) HID TROUGH SOUNDING/ 200 BT 1B00 PT 1600 PT DEPTH RANGE SPECIES X SPECIES X SPECIES X (n) (■=443) tfsara!teas maattart 48.8 Baatkasams glaciala 28.4 loo Argyragatacas kamigymaas 7.7 Argyragalacas a!faasi 4.1 Batascagatas kraayari 3.8 (■=13.638) (■=102) Iffcremcsfst/as gaatassaa 42.7 Haaraticas maa Hart 30.0 * Gadicalas argaataas tkari 35.2 tlicramasistias gaatassaa 48.6 - 4 0 -2 190-220* /fataaagrammas aeglefiaas 10.1 » Haliea!»»** éacUyagtarms 8.2 (■=228) (■=8461) tlicramasistias gaatassaa 64.0 Matascagatas kraayari 50-4 * tagidarkamkas wkiffiagaaas 8.8 tlicramasistias gaatassaa 39.8 280-3IO* Malicalaaas dactylagtaras 6.1 ffaattasama yiae tata 6.5 * tia Iva malva 3.1 * flafacacayka/as laevis 3.1 (■=363) (■=9439) (■=416) Micrmmasisliws gaatassaa 49.6 Matascagatas kraayari 82.8 Baatkasams glaciala 23.3 • Cktmaara maastrasa 11.8 tlicramasistias gaatassaa 11.1 Lamgaayctas era cadi tes 20.4 * Glygtacagkalas cyaagtmssas 7.7 Baatkasams glaciala 4.6 Stamias kaa ferax 11.3 397-414*/ apidmràamtas arkfffiagaaas 4.6 takiaackia gemellari 9.1 * Malva malva 3.2 Okae Hades siaaat 3.6 • HaUcataaas Sectylagtaras 3.1 Xeeedermickikys aegei 3.6 Sagamtcktkys sckaakaakacki 3.1 (•=506) (■=1732) • Ckimaan mams trisa 48.3 Hatascapalas ina y tri 24.2 * L apiliaa a faas 22.1 Laatpaayctas cracalitas 15.6 • HaUcataaas 4aet y lap taras 4.7 * Hafargyraas jakasaai (java) 12.5 * Blyptacapkalas cyaagtassas 4.7 S tamias kai Taras 8.7 598-637* Ep Igai as tatascapas 4.3 ffyctaptam piae ta tam 6.9 ■ Malva éyptarygia 3.2 Baatkasama glaciala 5.7 Halaaastigma attaaticam 5.1 Xaaahrmicktkys capai 3.7 Lakiaackia pama Hart 3.3 (■=989) Haaraticas maallari 52.6 700 Scapalagahs kasaii 10.4 Lampaayetas machlani 7.3 Baatkasama glaciala 6.6 Lampaayetas enaulis 4.4 Hsrmicktkys spsnsas 3.2 205- 5 0 -2 (■>«40) (■=963) * Carypkamaaiéas rapastris 36.0 Halaaastigma attaaticam 32.8 m Lapt lisa a faas 11.3 Hatascapalas kraayari 18.1 •Marasi ta aafaatis 10.1 Baatkasama glaciala 9.4 794-841 * Calais ma/astamas 8.2 * Syaapkakraackas àaapi (Java) 7.8 * Apkaaapas casha 5.2 Lampaayetas cracaéitas 3.5 • Alapacapkatas kitrii! 5.0 * Carypkaaaatéas rapastris 3.2 * Blyptacapkalas cyaagtassas 3.6 (•=1401) (■=539) * Afapacapàafas tafrii! 51.7 Lampaayetas machlani 28.0 * Carypkaamailas rapastris 20.2 Scapalagahs kasaii 15.6 * Apkaaapas caràa 4.4 Lampaayetas enaulis 10.6 • Hafargyraas jakasaai 3.9 Baatkasama glaciala 6.7 •Lapflfaa a gaas 3.2 Harmfcktkys aparasas 5.9 * Trachycaris Hamyi 3.1 Stamias kai Taras 4.8 • Harastii aa fia lis 3.0 Chaiitalis s tasai 3.3 Batkylagas aaryaps (dark) 3.2 Lakiaackia gams t lari 3.0 -206- and D. watasei -Nafpaktitis, 1978). The the sea-bed are scarce, but valuable. Cohen & generally large size of these demersal specimens Paw son (1977) observed the pseudoceenic of both the latter species was remarked upon by zoarcld, Melanostigma atlanticum, at Nafpaktitis et ai.O 977). 1960m, while Nafpaktitis etal., ( 1977) remark 3. Near bottom sampling is Improving our on large Lampanyctus macdonaldi swimming knowledge of the congruency of the pelagic and very near the bottom. demersal slope ichthyofauna. For example, initial trials of a near-bottom echo-sounder integrated INDIRECT APPROACHES with the I.O.S. net monitor for use with the RMT a Feeding studies 1+8 have already given promising results. While Demersal slope fishes have provided considerable this gear samples micronekton, the recent data on the occurrence of pelagic oceanic species preliminary investigations of the slopes of the in stomach contents. Assuming that most, at least, Rockall Trough, mentioned above, sampled a much were alive when eaten, and the condition of many larger size spectrum with a midwater trawl of seen personally suggest it, this is a useful means mouth opening 30m x 20m high and a bottom of assessing near-bottom faunal interaction. For trowi of 22m x 6m headline height. (Merrett et instance, a less than exhaustive examination of the al., 1986). literature on Atlantic collections revealed 34 Over a five day period, eleven demersal hauls species representing 18 families (14 bentho- were taken from both sides of the Trough at pelagic and 4 benthic) of demersal fishes approximately 200m intervals from 200 containing identifiable remains of 24 species 1000m soundings, and nine midwater hauls from from 10 families of meso-and bathypelagic fishes, similar localities were fished with the footrope b Parasite'tags'. 0- 10m ( I tow), 3- 18m (7 tows) and 60m ( I Markle & Wenner (1979) demonstrated the tow) above the seabed. In addition four dependance on the sea-bed of Melanostigma mid-Trough samples were taken ( 100,400, 700 atlanticum from a knowledge of its reproduc and 1000m depth) over 2550-2620m soundings tive biology and temporal changes in its endo- The total collection yielded some 40,000 fish paresitic fauna. The value of such parasite 'tags', (23,000 mesopelagic and 17,000 demersal) both internal and external, was further discussed belonging to 108 species. Nineteen species were by Campbell et al., ( 1980). The implications that peculiar to the mid-Trough catches and only 27 the parasite Infection rate among demersal fish > were common to both pelagic and benthic gears. mesopelagic fishes > bathypelagic fish in the However, only 38 species comprised >3£ of the current context are obviously interesting, catch in any one sample. The only mesopelagic c Eggs and larvae species to be ranked among demersal catches was Studies of eggs and larvae offer another worthwile Micromesistius poutassou, which is perspective of research. Data are sparse, but consistent with its known tendency to impinge on work on Lampanyctodes hectoris from off the slope es this traverses its depth distribution southwest Africa and New Zealand has identified (Bailey, 1982). Only in pelagic tows over the eggs and larval stages and shown that both occur slope were demersal species (3) present in over the outer shelf and slope in I4-15*C water sufficient proportion to warrant inclusion, after spring spawning (Ahlstrom et al., 1976; despite the close proximity to the bottom of the Robertson, 1977). The distinctive eggs of pelagic trawl (Table II). This is the first Maurolicus muelleriaee well known. In the substantial observation, despite obvious sampling North Atlantic and off New Zealand they are limitations, that the bulk of the demersal and spring-summer spawners with eggs and larvae pelagic fish populations remain separate over the occupying l00-500m levels and temperatures of slope, with the former evidently swimming in 8-22‘C (Williams & Hart, 1974; Robertson, layers very close to the bottom, 1976). Off Japan Okiyama (1971) observed the b Submersibles. majority of eggs In the surface layers (0-50m), Reports of pelagic oceanic fishes observed close to with few larvae above 75m depth. In ali three -207- examples distribution was centred over slope -BADCOCK, J., 1981. The significance of meristic waters, though the North Atlantic observations variation in Benthosema glaciale (Pisces, Mycto- were from the thalossobathyal fauna. Hamann at phoidei) and of the species distribution off northwest a1.,( 1981) investigated hydrographic effects on Africa. Deep-Sea Ros., 28h : 1477-1491. larval distribution in the Mauretanian upwelling -BAILEY, R. S., 1982. The population biology of blue area and found highest concentrations over the whiting in the North Atlantic. Adv. mar. Bio!.. Iff. 257-355. slope with good correlation between Myctophum -BAIRD, R. C., 1971. The systematics, distribution, punctatum larvae and water masses (cf. above). and zoogeography of the marine hatchetfishes (Family Conversely, ontogenetic descent from the surface Sternoptychidae). Bull. Mus. comp. Zool. Harv., waters of the pelagic larvae of demersal species M2{ 1) : 1-128. Coryphaenoides spp. has been demonstrated -BERTELSEN, E.. G. KREFFT 8. N. B. MARSHALL, from RMT 1 ♦ 8 collections (Merrett, 1978). 1976. The fishes of the family Notosudidae. Dana Extension of the above studies to investigate Rep., 06 : 114 pp. reproductive patterns would aiso be beneficial, -CAMPELL, R. A.. R. L. HAEDRICH S. T. A. MUNROE. d Diet and morphological variation I960. Parasitism and ecological relationships among Clarke ( 1984) postulated the separation of two deep-sea benthic fishes. Mar. Biol., 57:301-313. sexually dimorphic species of snipefish previous -CLARKE, T. A., 19B4. Diet and morphological ly recognised es Macrorhamphosus scolopax variation in snipefishes, presently recognized as Macrorhamphosus scolopax, from southeast on these criteria. Australia: evidence for two sexually dimorphic Thus, while Improved sampling techniques and species. Copeia, 1904 (3) : 595-608. increased effort are necessary to elucidate many -COHEN, D. M., 1963. A new genus and species of of the complexities of biogeographica! congruence bathypelaglc ophidioid fish from the western North around the oceanic rim, a variety of ecological Atlantic. Breviora, 196 : 8pp. pointers are aiso available to complement this -COHEN, D. M. 1974. A review of the pelagic ophidioid endeavour substantially. fish genus Brotulataenia with descriptions of two new species. Zool. J. Linn. Soc., 55(2) : 119-149. -COHEN, D. M. & D. L. PAWSON, 1977. Observations ACKNOWLEDGEMENT from the DSRV Alvin on populations of benthic fishes and selected larger invertebrates in and near The manuscript benefitted greatly from helpful DWD-106. Baseline Rep. Environm. Conditions Deepwater Dumpsite 106. U.S. Dap. Comm., comments by Martin Angel, Julian Badcock NOA A, Dumpsite Evaluation Rep., 77 -1,2 (I.O.S.) and Ken Sulak (Huntsman Marine Bioi. Char act. : 423-450. Laboratory, Canada). I am grateful to them ali. -EBELIN6, A. W., 1962. Melamphaidae. 1. Systematics and zoogeography of the species in the balhypelagic fish genus Melamphaes Gunther. Dana-Rep. 50 : REFERENCES 164pp. -GJOSAETER, J., 1984. Mesopelaglc fish, a large potential resource in the Arabian Sea. Deep-Sea -AHLSTROMI, E. H., H. G. MOSER & M. J. O’TOOLE, 1976. Development and distribution of larvae and Res., 3/ : 1019-1035. -GJOSAETER. J. & K. KAWAGUCHI, 1980. A review early juveniles of the commercial lanternfish, of the world resources of mesopelaglc fish. 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On the Identity and pelagic : 561-575. occcurrence of larval and juvenile stages of rattail -HARGREAVES, P. M.. 1984. The distribution of fishes (Family Macrouridae) from 60*N, 20’W and Decapoda (Crustacea) in the open ocean and 53'N, 20*W. Deep-Sea Pes., 2S: 147-160. nearbottom over an adjacent slope in the northern -MERRETT. N. R.. S. EHRICH, J. BADCOCK 6. P. A. North-easi Atlantic Ocean during autumn 1979. J. HULLEY, 1986. Preliminary observations on the mar. bio/. Ass. U.K., 64: 829-857. near-bottom Ichthuofauna of the Rockall Trough: a -HUBBS, C. L. & T.l WAMOTO. 1977. A new genus contemporaneous investigation using commercial (Mesobius), and three new bathypelagivc species of sized mtdwater and demersal trawls to 1000m Macrouridae (Pisces, Gadiformes) from the Pacific deepth. Proc. R. Soc. Edinb., 88b : 312-314. Ocean. Prea. Ce/if. Acad. Sei., 4i (7) : -MUKHACHEVA, V. A.. 1981. Geographical distrib 233-251. ution and variability of Maurolicus meullert (Gmelini -HULLEY, P. A.. 1981. Results of the research (Stenoptychidae, Osteichthyes). In: Fishes of the Open cruises of FRV 'Wallher Herwig'to South America. Ocean. Inst. OceanoL, Acad. Sei., USSR : LVIII. Family Myctophidae (Osteichthyes, Myctophi 41-46. (In Russian). formes). Arch. Fisch. Wiss., J/: 11-300. -NAFPAKTITIS, B. C., 1978. Systematics and -ISAACS, J. 0. L R. A. SCHWARTLOSE, 1965, distribution of lanternfishes of the genera Lobianchia Migrant sound scalterers: interaction with the sea and Diaphus (Myctophidae) In the Indian Ocean. Nat. floor. Science, i50: 1810-1813. Hist. Mus. Los Angeles County, Sei. Bull., -JAHN, A. E. & R. H. BACKUS. 1976. On the 30 : 92pp. mesops!agic fish faunas of Slope Water, Gulf Stream, -NAFPAKTITIS. B. G.. R. H. BACKUS. J. E. CRADDOCK, and northern Sargasso Soa. Deep-Sea Res., 23 : R. L. HAEDRICH, B. H. ROBISON & C. KARALLA, 1977. 223-234. Family Myctophidae. In: R. H. 6ibbs Jr. (ed.) Fishes of -KAWAGUCHI. K. 8, H. SHIMIZU. 1978. Taxonomy and the western North Atlantic. Mem. Sears Fdn mar. distribution of the lanternfishes, genus Diaphus Ros., IO): 13-265. (Pisces, Myctophidae), in the western Pacific, -NIELSEN, J. G.. 1969. Systematics and biology of the eastern Indian Ocean and the southeast Asian sea. Aphyonidae (Pisces, Ophidioidea). Galathea Rep., Bull. Ocean Res. Inst. Univ. Tokyo, IO'. 145pp. IO: 1-89. -KREFFT, 6., 1974. Investigations on midwater fish in -NYBELIN, 0., 1948. Fishes collected by the the Atlantic Ocean. Bar. dt. wiss. Komma 'Skagerak' Expedition In the eastern Atlantic 1946. lieeresForsch., 23: 226-254. Gdteborgs K. Vetensk. vitterh. - Samh. -KREFFT, G., 1980. Results of the research cruises of Handi., (B), 5(16) : 1-95. the FRV ‘Wallher Herwigi Io South America. LUI. -OKIYAMA, M., 1971. Early life history of the Sharks from the pelagic trawl cathes obtained during gonostomatld fish, Maurolicus moutieri (Gmelini, in Altantic transacts, Including some specimens from the Japan Sea. Bull. Japan Soa reg. Fish. Res. other cruise. Arch. Fisrh.Wiss., 30{ 1) : 1-16. Lab., 23: 21-53. -KREFFT, G. 1985. Alepocephalidae (Osteichthyes. -PARIN, N. V., 1984. Oceanic ichthyologeography: an Argentlnoldea) drefer Relsen der Ftecherelforschungs- attempt to review the distribution and origin of schiffe ‘Anton Dohrn* und *Walther Herwigi in den pelagic and bottom fishes outside continental shelves Nordatlantlk. Arch. Fisch. Wiss.. 36 : 213-233. and neritfc zones . In: A. Post (ed.) Advances In -MARKLE, 0. F. 8. C. A. WENNER, 1979. Evidence of Ichthyology. Contributions Io the Fourth Congress of demersal In the mesopelaglc zoarcld fish European Ichtyologists held In Hamburg, September Melanostigma atlanticum with comments on demersal 1982. Arch Fisch. Wiss., 35: 5-41. spawning In the alepocephali fish Xenodermichthys -PARIN, N. V., 1986. Distribution of mesobentho- copei. Copeia, (2) : 363-366. pelagic fishes in slope waters end around submarine -MARSHALL. N. B.. 1973. Family Macrouridae. In: D. rises. This volume. M. Cohen, (ed.) Fishes of the western North Atlantic. -PARIN, N. V. 8. 6. A. 60L0VAN, 1976. Pelagic Mem. Sears Fdn mar. Ros., t (6) : 496-665. deep-sea fishes of the families characteristic of the -MARSHALL, N. B. 8, N. R. MERRETT, 1977. The open ocean collected over the continental slope off existence of a benthopelaglc fauna In the deep-sea. In: West Africa. Trans. P. P. Shirshov Inst. M. V. Angel (ed.) A Voyage of Discovery. George Oceano/., 104: 250-276. Deacon 70th Anniversary Volume. Suppl. -RINGREE, R. D. 6. G. T. MARDELL, 1981. Slope -209- turbulence, internal waves and phytoplankton growth at the Celtic shelf-break. Phil. Trans. R. Soc. Lomi.. K302-. 663-682. -ROBERTSON, D. A.. 1976. Planktonic stages or Maurolicus moutieri (Teleostei: Stenolychidea) in New Zealand waters. N.Z. J. mar. Treshw. Res., !0{2): 311-328. -ROBERTSON, 0. A.. 1977 Planktonic eggs of the lanternfish, Lampanyctodes hectoris (family Myctophidae). Deep-Sea Res., 24\ 849-852. -STEIN, D. L., 1985. Towing large nets by single warp at abyssal depths: methods and biological results. Deep-Sea Res., 32: 183-200. -WILLIAMS. R. 8, P. J. B. HART, 1974. Vertical and seasonal variability of fish eggs and larvae at Ocean Waters Station ‘India’, pp. 2333-243. In: J. H. S. Blaxter (ed.) The Early Life History of Fish. Springer-Verlag, Berlin : 233-243. -WISHNER, K. F., 1980.The biomass of the deep-sea benthopelagic plankton. Deep-Sea Ros., 27A : 203-216. -WIStÆR. R. L.. 1977. New data on the rara alepocephali fish Photostylus pycraterus. Bull, south. Calif. Acad. Sei., 75: 153-158. -210- MONSOON REGIME IN THE INDIAN OCEAN AND ZOOPLANKTON VARIABILITY VIJAYALAKSHMI R. NAIR National Institute of Oceanography, Versova, Bombay, India INTRODUCTION the group is concerned. Higher abundance of the group/species is observed along the north eastern The effect of the monsoon in the Indien Ocean ie part of the Indian Ocean (Bay of Bengal) during limited to north of 10'S, the area being defined as tile SW monsoon, when the circulation Is from the region of seasonally changing monsoon gyre west to east. During the NE monsoon period, the (Wyrtki, 1973). The southwest monsoon (SW) is flow is reversed and the relatively higher prevalent from May to September when the population existing in the eastern side begins to cyclonic circulation in the surface waters of the spread along the west coast of the Indian Arabian See and Bey of Bengal results in water peninsula. Thia is well marked in the movement from west to east. The wind direction Is zoogeography of Sagitta bedoti, S. bipunctata, reversed during the northeast monsoon (NE) S. en flata, Spacifica, S. regularis and S. period extending from November to March and the robusta {Nair, 1972; 1977)(Table I). gyre becomes anttcyclonic leading to a circulation On the western side of the Arabian See, as a from east to west. The monsoonal effects on result of its reversal, the Somali current zooplankton lead to characteristic zoogeographic transports zooplankton meridionally across the patterns in the open ocean and coastal waters. equator both in southern and in northern Studies of zooplankton variability were taken up directions according to the time of year. The since the International Indian Ocean Expedition samples collected during theLusiad Expedition in (1960-65) and later surveys made by the July/September 1962, along the equatorial National Institute of Oceanography (Rao, 1979; region of the Indian Ocean with north-south Rao et al. ,1981). The various aspecta presented transects covering the equatorial Current System tiere are based mainly on the author's show this (Nair, 1976). Common groups and Investigations covering a period of about fifteen different species of Chaetognatha reach maximum years. The evaluation is presented In three population density west of 57*E, suggesting a sections to show how the monsoon exerts its meridional distribution on the western side and a Influence on zooplankton from different types of zonal distribution along the remaining part of the environment. equatorial zone (Fig. 1). Upwelling enriches the Somali waters during the SW monsoon period and the current carries part of the dense population OPEN OCEAN seen off Somalia towards the eastern part. The reversal of the monsoon circulation is one of the most important factors affecting the abundance OQASTAL WATERS and diversity of zooplankton In the open ocean and is reflected in the relativa abundance of total The coastal waters of the tropics are highly zooplankton biomass (IOBC, 1968) and common productive and sustain a rich and abundant groups like Copepoda (IOBC, 1970), Chaetognatha plankton life. This area Is aiso Influenced by the (Nair, 1972), pelagic tunicates (Nair & Iyer, seasonal variations in rainfall on account of the 1974), decapod larvae (IOBC, 1970), pelagic monsoon. Here the monsoonal effect is more molluscs (IOBC, 1971) and others. This is true during the SW monsoon (June to November) when whether the entire group or a species belonging to freshwater influx from rivers end estuaries Table I Average number or different species In the Arabian Sea with average numerical values of the selected 5’ squares. Species AREA 1 AREA 2 AREA 3 AREA 4 O0-15TI & 50-55’E) (20-2S-N & 65-70'E) (15-20‘N & 70-75*E) (5-10'N 6 75-80*E) NE SW TOTAL NE SW TOTAL NE SW TOTAL NE SW TOTAL K.pacifica 27.86 11.15 39.01 13.45 14.50 27.95 31.24' 43.20' 74.44 22.53 32.70 55.23 K.subtilis 2.61 21.99' 24.60 1.62 -.— 1.62 1.00 — 1.00 12.53' 5.28 17.81 Petraea 116.26 78.90 195.17 3.54 6.50 10.04 58.61 30.70 89.31 130.88* 180.07 310.95 S.hadaii 381.90' 215.94 597.84 116.51 31.30 147.81 75.06 21.05 96.11 232.78 505.37 738.15 S.bigradata 76.09 B4.28' 160.37 75.71 9.80 85.51 168.23* 22.70 190.93 80.90 19.85 100.75 S. sanata 1865.47' 1423.34 3288.81 682.77 211.40 894.17 905.43 416.75 1322.18 1315.37 2520.28' 3835.65 S.fara* 2.69 26.07 28.96 0.14 8.20 8.341 5.66 23.80 29.46 8.92' 4.43 13.35 -HZ- S. kaxaptara 17.26' 17.92 35.18 0.24 0.10 0.34 4.20 1.00 5.20 12.69 19.85' 32.54 S.atialata 4.44* 12.92- 17.36 0.10 -.— 0.10 — — — 1.08 -.— 1.08 S.aagiacta 8.94 65.29 74.23 94.74' 11.40 106.14 10.66 15.10 25.76 32.53 75.97" 108.50 S.pacifica 164.78 274.23 439.01 62.50 19.10 81.90 190.00' 18.95 208.95 184.41 425.54' 609.95 S.pulchra 21.65' 22.45 44.10 11.97 0.30 12.27 2.53 3.30 5.83 9.38 27.85* 37.23 Scapularis 67.60 71.82 139.42 1.96 18.10 20.06 146.45' 25.00 171.45 47.22 150.23* 197.45 S.rshasta 98.68' 84.82 183.50 7.71 4.50 12.21 17.38 1.85 19.23 8.69 86.11' 94.80 TOTAL 2856.54 2411.12 5267.66 1072.96 343.70 1416.66 1617.91 623.40 2241.31 2108.11 4053.53* 6161.64 ' Maximum observed value during the SW monsoon period ’ Maximum observed value during the NE monsoon period -212- durlng the SW monsoon period (June - September) makes the region an excellent pasturage for the plankton feeders and in general, the peak fishing season along the coastal waters coincides with this period (Nair, 1982). Along the east coast there is an increase In the biomass of zooplankton from north to south whereas a reverse pattern has been observed during October to November along the west coest (Nair, 1977). The incidence of high densities of chaetognaths along the two coasts aiso follows a similar pattern. Along the west coast, off Bombay the population maximum of chaetognaths was seen In November-December (Nair et al., 1981), south of Bombay, off Calicut in October - November and further south at Trivandrum the peek observed was much earlier (July - September). On the east coast, the peek periods for the chaetognath species were found off Madras during May - August, and towards the South in the Oulf of Manner it was in November and December (Rao et al., 1981). The prevailing difference in salinity, periods of upwelling and surface currents may contribute to this pattern of abundance. Upwelling along the west coast starts in March and continues during the SW monsoon with its maximum effect in August - September. It sets in earlier in the south and gradually extends to the north ( Rao, 1979) and concomitant with this, the movement of peek zooplankton abundance is aiso from south to north. ESTUARIES Fig. 1 Distribution of (A) total zooplankton, The monsoon exerts stress on estuarine fauna by chaetognath volume, phosphate phosphorus and ( B bringing about a drastic changa in salinity, which to I) different species of Chaetognaths along the was more marked towards the upper reaches. equatorial east-west transect of the Lusiad During the high salinity period zooplankton Expedition in the Indian Ocean (a, total maintained a high level of production of about 3 to zooplankton: b, chaetognath volume and c, 7.5 times that of the relatively low standing stock phosphate phosphorus). of zooplankton observed during the low salinity period (Nair, 1982). lower tile salinity along the coast to 30-34.5°/oo. The low saline fauna replacing the high saline In general, throughout the Indian coastal waters species are not at ali diverse or rich in the annual zooplankton distribution Is bimodal comparison (Rao et al., 1981). Neritlc species with two peaks - one Just before the monsoon and Uka Sagitta bedoti penetrate to the upper the other Just after the rain. (Rao, 1979, Rao at reaches of the estuarine system during the al., 1983). The plankton production triggered premonsoon period when a uniform salinity ( 25.3 -213- - 33.5°/oo) prevailed throughout the system Puhi. UNESCO/NIO : 168-195. (Nair, 1974). In the postmonsoon period the •NAIR, V. R.. 1977. (issued in 1982). Contribution of chaetognath population synchronically followed zooplankton to the fishery potential of some the steep gradient in salinity (0.2 to 28.6°/oo) environments. J. Indian Fish. Ass., 7 (1-2 ) : along the estuary end became restricted to its 1-7. -NAIR, V. R.. S. N. GAJBHIYE & B. N. DESAI. 1981. seaward end. Distribution of chaetognaths in the polluted and unpolluted waters around Bombay. Indian J. mar. Sei.. IO (1): 66-69. CONCLUDING REMARKS -NAIR. V. R„ S. N. GAJBHIYE S. F. H. SAYEO, 1983. Variations in the organic carbon content of In the open ocean the semi annually reversing zooplankton in the nearshore waters of Bombay, system of currents exert profound influence on Maharashtra. Indian J. mar. Sei., 12: 183-185. the shifting of zooplankton populations. The -NAIR, V. R. &. H. K. IYER, 1974. Quantitative assumption Is bæed on samples mostly collected distribution of copeletes, salps and doliolids (pelagic from the upper 200m of the Indian Ocean and the tunicates) in the Indian Ocean. Indian J. mar. Sei., limit of such influence is yet to be ascertained In J(2) : 150-154. the aestal waters the time lag Involved In the -RAO, T. S. S . 1979. Zoogeography of the Indian north to south or reverse pattern of movement of Ocean. In: S. van der Spoel & A. C. Plerrot-Bults (eds) Zoogeography and diversity of plankton. species along with associated factors responsible Bunge sciani. Publ.. Utrecht: 254 -292. for such variability calls for detailed -RAO. T. S. S.. V. R. NAIR & M. MADHUPRATAP. investigation Estuaries with the characteristic 1981. Ecological considerations on tropical fluctuations in salinity on account of monsoon and zooplankton. Proc. Symp. Eco/. Anim. Popt/I. the theory of repopulation are aspects to be enoi. Surv. India., /: 15-39. studied in detail -WYRTKI, K.. 1973. Physical Oceanography of the Indian Ocean. In: B. Zeltschel (ed ). The biology of tha Indian Ocean. Vol. 3. Springer verlag, Berlin REFERENCES - Heidelberg - New York: 10-36. ~IOBC i960, flaps on Iola! zooplankton biomass in the Indian Ocean. NOE Plinioi) Al/ts. /(2) . NIP. CSIR. New Delhi : 18pp. -I06C. 1970. Distribution of copepods and decapod larvae In the Indian Ocean. / tOE Phnkton Atlas 2 (1): NIO.CSIR, COA : 22pp. -I06C. 1971. Distribution of planktonic Molluscs of the Indian Ocean. NOE Plankton Allas. J (2): NIO, CSIR. Goi : 40pp. -NAIR. V. R., 1972. Variability in distribution of chaetognaths In the Arabian Sea. Indian J. mar. Sei., / : 85-80. -NAIR, V.R., 1974. Distribution of chaetognaths along the salinity gradient in the Cochin backwater, an estuary connected to the Arabian Sea. J. mar. bid. Asa. India, 16 (3): 721-730. -NAIR, V.R., 197ft. Species diversity of chaetognaths along the equatorial region of the Indian Ocean with comments on the community structure. Indian J. mar. Sei. 5(1): 107 -122 -NAIR, V. R., 1977. Chaetognaths of the Indian Ocean Proc. Symp. Warm Watar loop linki Spet -214- models AND PROSPECTS OF HISTORICAL BIOGEOGRAPHY GARETH NELSON American Museum of Natural History, New York, U.S.A. The distribution of organisms may be considered biogeography is an attempt, for better or worse, from various points of view, which reduce to two: to marry the two ( Nelson & Rosen, 1981 ; Nelson ecology and systematics. Each has b history of & Platnick, 1981). These attempts mery aiso about 200 years, the former beginning with prove vain, but at the moment not yet (Patterson, Humboldt, the latter with Candolle (Nelson, 1 983). 1978; Browne, 1963). Ecology sees causal An element common to these attempts Is to explanation in measurable factors of the visualize systematic relationships not in terms of environment - elevation, temperature, latitude, fossil ancestors and living descendants but as depth, salinity, etc. Systematics sees it in descendants only. This view is not problematic, historical circumstance - in evolution in some for ali ancestors are aiso descendants. Viewed as sense - because the ecologie factors, even in their such they differ only in degree of relationship. totality, ara always insufficient. A species rarely, Thus taxu 3 and 4 (Fig. 1 ) may be viewed as if ever, lives everywhere that is ecologically related to each other more closely than to taxa 1 suitable. and 2. Such Is true even If 3 Is the ancestor of 4, I focus on the systematic aspect. How do we or vice verse; or if 1 is the ancestor of 2, or 2 of discover historical circumstance and acquire the 3, or whatever. Geographically the idea is that the knowledge needed for satisfactory explanation? relationships of taxa might indicate the historical Traditionally it was hoped that this knowledge relationships of the geographic areas. If so, areas would emerge from study of the fossil record This C and D ara related to each other more closely than has proved a vain hope, not merely because the to areas A and B, according to the evidence of the fossil record is incomplete, but because data of the interrelationships of taxa 1-4, where taxon 1 record do not contain the knowledge. To overcome occurs In ares A, taxon 2 in area B, etc. However this deficiency fossils were often viewed as simple to understood, this model is not a ancestors of recent taxa. This presumed description of biological distribution as we find it. relationship, reed into the data of the rscord, was The model merely illustrates a particular notion sometimes, and sometimes stilt is, believed of erœ relationship. This notion is important, for crucial evidence of historical circumstance. But this belief, in crucis evidence, has aiso proved Species Areas vain. Ancestors and their géographie analogs - centers of origin - arii not empirical entities that 1A 2B 3C 4D A B C D await discovery (Nelson, 1983a). Rather, they are constructs - one might even term them artifacts - arising from a particular view of systematics (Nelson A Platnick, 1984a). These vanities have become clear to many persons Tor marry reasons. Cladlstic systematics is one attempt to remedy the problem (Eldredge & Cracraft, 1980; Funk & Brooks, 1981; Wiley, 1981; Fig. 1 A: Oladogrem of four taxa (species 1 -4) in Platnick & Funk, 1983). Panbiogeography is four arae (A-D). B: Corresponding area another (Croizat, 1958, 1964). Ylcariance ciadogram (after Nelson, 1982, Fig. 1 ). -215- It is the basis for the analytical procedures of two levels may be largely decoupled, if so, the Cladistii and vicariance. history of pelagic distribution mery forever be A different notion is based on similarity of elusive to a vlcarlant interpretation. biota. As an example I mention an analysis of the If we turn to geotectonics we find conflicting distribution of cowries, genus Cypraea , views. In contrast to the classic drift theory, occurring in four areas: Japan, Philippines, New earth expansion holds that the modern Pacific Caledonia, Queensland (Nelson, 1984a). If we Basin began, 8s did the Atlantic and Indian Basins, count the species common to pairs of areas, the by continental rifting in Mesozoic time (Carey, Philippines and Quyeensland have the highest Î976, 1983). A kind of hybrid theory, of number. We might believe that these areas are "Pacifica", holds, es does the classic view, tirai the related on this evidence - the high number of taxa Pacific Is the oldest ocean, but that It contained a common to them. If so, we would have a different continental mass that rifted into fragments, which notion of area relationship, which is independent eventually dispersed around the modern basin of any Cladistii information. (Nur & Ben-Avrahem, 1978). in support of these Yet another notion is that formalized by Hennig views is the known age structure of the world sea ( i 966): the progression rule. Geographic floor - about the same in ali three ocean basins distributions are treated 8s characters, and (Pitman et al., 1974). distributions are assigned to hypothetical These are themes relevant to Croizat's synthesis ancestors, so es to minimize dispersais (Nelson, of terrestrial distribution, in which there Is 1969;Nelsoni Platnick, 1984b). Interestingly, symmetry of transoceanic relationship across ali most of the clues, or rules, historically used to three basins. In addition there are boreal 8nd determine a center of origin, reduce to this Antarctic patterns, making a total of five major formalization, which is constrained by cladistic types of distribution. information (Platnick, 1981). Unfortunately, the These are themes relevant to pelagic progression rule is biased so as always to resolve biogeography, for the question here is the relative a center of origin, even when no center of origin age of origin of the deep ocean basins and the need have existed (Nelson, 1975). open-water habitat. If the distribution of pelagic Ylcariance biogeography attempts to focus on the organisms reflects anything of history, why not cledistic information, in the hope that this the history of the basins? So, what are the information, when cast geographically, will have patterns? and to what history do they testify? validity across taxa, and across the gulf that My approach is not through the study of pelagic separates biological evolutaion from geological distribution, but through a particular family of evolution. In this regard vicariance takes fishes, Engraulidae (anchovies). Of some 150 inspiration from Croizat, who tirelessly stressed species, there is perhaps one that has a pelagic, that earth and life evolve together; that life is but rather than Inshore or freshwater, habit. It is the superficial layer of the rocks; that taxonomic widely distributed throughout the Indian and differentiation is life's response to a dynamic West-Central Pacific Oceans, and it has the most geology. widespread distribution of any anchovy. Perhaps These slogans are imbued with the wishful it evidences the decoupling of the pelagic from the thought, which Croizat stressed es empirical fact, shelf, yet the species, Encrasicholina that life is tightly bound to, and ordered by, the punctifer- Stolephorus buccaneeri, is not earth's tectonic history. Croizat did not deal with ubiquitous in tropical oceans. Its eastern limit is pelagic distribution, which is complicated by a the East Pacific Barrier ; and its western, the Capo second level of tectonics - the structured of Good Hope; in these respects it is not unusual. water-messes, the boundaries of which frequently Anchovies are interesting because they show limit the geography of taxa. The processes at the much the same, apparently trans-Pacific, geotectonic level ultimately determine events at relationship as many marine groups, including the hydrotectonic level, and perhaps the relation the Spanish mackerels (Collette & Russo, 1985), is firmly deterministic. On the other hand, the end Ura epipelagic sergestid crustacean Acetes -21Ö- (Omori, 1975), which is differentiated in the laterally. I do not claim that anchovies prove the New World along both coasts of the Americas and Pacifica model, or eerth expansion, but they seem in South American freshwater es well. Anchovies an example of a group differentiated in response to do much the same but on a grander scale. Some 70 a growing rather than shrinking Pacific Basin. species ere involved in the New World And they illustrate a vicariant approach to differentiation, with more than 20 of them biological distribution that if not truly pelagic, at confined to South American freshwater, which is least borders on being so. unique in this respect. There are few, if any, Anchovies are interesting because their freshwater anchovies elsewhere. The details of terminal differentiation 13 bound with the relationship seem to confirm, and possibly Pliocene closure of the Panamanian Isthmus, extend, the notion of interoceen connection (Van suggesting a progressively older history for the der Spoel, 1983; Yan der Spoel & He/man, South American freshwater, the bipolar 1983). (antitropical), and the trans-Pacific patterns The trens-Pacific character of this distribution (Nelson, 1984b). But how old? was not clear, for the traditional taxonomy of the A review of the fossil anchovies (Grande & group broke into Old World end New World Nelson, 1985) was not much help, but showed sections. Cladistic analysis of the group associated that the oldest, from the Upper Miocene of some Old World forms ( from the West and Central Cyprus, is very similar to the Mediterranean Pacific) with those of the New, end the anchovy of todey. The group most closely related to trans-Pacific draracter became evident. anchovies, the herring family Clupeidae, is known Interestingly, the West-Central Pacific section is from abundant fossil remains from the beginning a small one, with only five species (one endemic of the Tertiary. If this relationship is correct, in Hawaii), in contrast with the New World then anchovies are older still, even though their section, with a relatively massive radiation in the fossil record is very meager. tropics, involving a dozen or more species Even with few fossils, and from them no sympatric, and typically collected together, in information not already supplied by recent areas like the Gulf of Panema (Hildebrand, 1943; species, modern taxa and the distributions of Nelson, 1983b). anchovies and many other groups ere ample, on a Seemingly anomalous, and embedded in this world-wide basis, snd promise to be richly trans-Pacific distribution, is the genus informative. The key to the systematic Engraulis, a world-wide genus with temperate information - knowledge of the interrelationships representatives in arees of classic concern of tira species-leve! taxa (andof the supraspecific (Nelson, 1985), occurring there with sardines groups) - Is the promise of cladistlcs. Suffice It and other epipelagic organisms (Hedgpeth, to say that enough progress has been achieved, 1957). with anchovies and other groups of plants and Bipolarity, or antitropicality, is interesting. animals, to justify an optimistic outlook for the There are two reviews of nota (Ekman, 1935;Du future. Rietz, 1940). Here the Pacific Basin is relevant, There Is a historical factor inherent In for the distributions of individual taxa, when geographic distribution, in the pelagic as considered together, outline the Pacific Basin elsewhere. At present it is largely confounded fairly exactly, be the taxa terrestrial plants or with variation properly termed ecologie, and our marine animals. So we are led to œk if bipolare notions of ecology are, es a result, overextended is a reflection of the development of the Pacific and on occasion whimsical. Surely it would be Basin. Anchovies testify that such is the case. better if this historical factor could be identified As revealed by a «-floor spreading data, the and isolated. It is time that this task be taken Pacific is unique in its extensive north-south seriously, not only by systematics (who do the spreading, as reflected particularly In the work) but aiso by ecologists (who profit from it). Pacifica model. The basin expands radially, in contrast io the other basins, which expand -217- REFERENCES Comments on the history or biogeography. J. Hist. Biot., it-. 269-305. -BROSME, J., 1983. The secular ark: Studies in -NELSON, G.. 1982. Cladistii et blogeographle. C.R. the history of biogeography. Yale University Soc. Biogeogr., 56■ 75-94. Press, New Haven : 273pp. -NELSON. 6., 1983a. Vicariance and cladlstlcs: -CAREY. S. W.. 1976. The expanding earth. Historical perspectives with implications for the Elsevier Press, Amsterdam : 468pp. future. In: R. W. Sims, J. H. Price 8i P. E. S. Whailey -CAREY. S. W. (ed.). 1983. The expanding earth: (eds). Evolution, time and space: The A symposium. Univ. Tasmania, Hobart : 423pp. emergence of the biosphere. Academic Press. -COLLETTE, B. B. 6 J. L. RUSSO. 1985. Inter London: 469-492. relationships of the Spanish mackerels (Pisces: -NELSON. 6.. 1983b. Anchoa argentivittata, with Scombridae: Scomberomorus) and their copepod notes on other Eastern Pacific anchovies and the parasites. C/adistics, /: 141-158. Indo-Padfic genus Encrasicholina. Copeia, 1903 : -CROIZAT. L., 1958a. Panbiogeography. Published 48-54. by the author, Caracas, vol. 1: 1-1018. -NELSON. G., 1984a. Cladlstics and biogeography. In: -CROIZAT, L„ 1958b. Panbiogeography. Published T. Duncan & T. F. Stuessy (eds), C Jadis tics: by the author, Caracas, vol. 2 : 1-1731. Perspectives on the reconstruction of -CROIZAT, L„ 1964. Space, time, form: The evolutionary history. Columbia Univ. Press, New biological synthesis. Published by the author. York: 273-293. Caracas : 881pp. -NELSON, 6., 1984b. Identity of the anchovy -OU RIETZ, G. E., 1940. Problems of bipolar plant Hildebrandichthys setiger with notes on relationships distribution. Acis Phytogeogr. Suecica. /J: and biogeography of tho genera Engraulis and 215-282. Cetengraulis. Copeia, 1984: 422-427. -EKMAN, S., 1935. Tiergeography des Meeres. -NELSON. G.. 1985. A decade of challenge: The future Akad. Verlagsgesell., Leipzig : 542pp. of biogeography. In: Plate tectonics and -CLDREGDE, N. & J. CRACRAFT, 1980. biogeography. Am. Ass. Adv. Sei., Earth Sei. Phylogenetic petterns and the evolutionary History 4 (2) : 187-196. process: Method and theory in comparative -NELSON. G. 8. N. PLATNICK. 1981. Systematics biology. Columbia University Press, New York : and biogeography: C/adistics and vicariance. 349pp. Columbia Univ. Press, New York : 567pp. -fUNK, V. A. 8. D. R. BROOKS (eds), 1981. Advances -NELSON. G. 8, N. PLATNICK. 1904a. Systematics and in dapsiles: Proc. first meeting Willi Hennig evolution. In: M.-W. Ho 8< P. T. Saunders (eds), Society. New York Botanical Garden, Bronx : 250pp. Beyond Neo-Darwinism: An introduction to -GRANDE, L. 8, G. NELSON. 1985 . Interrelationships the new evolutionary paradigm. Academic oT fossii and recent anchovies (Teleostei: Press. London: 143-158. Engrauloidea) and description of a new species from -NELSON. G. 8, N. PLATNICK. 1984b. Biogeography. the Miocene of Cyprus. Am. Mus. Novitetes Carolina Biology Readers, t/9. Carolina 2826: 1-19. Biological Supply Co., Burlington: 1-16. -HEDGPETH, J.. 1957. Marine zoogeography. In: -NELSON. G. 8. D. E. ROSEN, (eds). 1981. Vicariance J.W.HED6PETH (ed.). Treatise on marine ecology biogeography: A critique. Columbia University end peleoecology, vol. I. Geol. Soc. Amor ice, Mam. Press. New York : 593pp. 67(1) : 359-382. -NUR, A. 8, Z. BEN-AVRAHAM. 1978. Speculation on -HENNiG, W., 1966. Phylogenetic systematics. mountain building and the lost Pacifica continent. J. University of Illinois Press, Urbana : 263pp. Physics Earth, Suppt., 26 : 21-37. -HILDEBRAND. S. F , 1943. A review of the American -0M0RI. M„ 1975. The systematics, biogeography anchovies (Family Engraulidae). Bull. Bingham and fishery of epipelaglc shrimps of the genus Acetes Oceenogr. Coli, B{2): 1-165. (Crustacea, Decapoda, Sergestidae). Bull. Ocean -NELSON, G.. 1969. The problem or historical Res. Inst. Univ. Tokyo, 7\ 1-91. biogeography. Syst.Zoot. IB: 243-246. -PATTERSON. C., 1983. Aims and methods' In -NELSON. 6.. 1975. Historical biogeography: An biogeography. In: R. W. Sims, J. H. Price 8> P. E W. alternative formalization. Syei. Zooi, 23 : Whailey (eds), Evolution, time and space: The 555-558. emergence of the biosphere. Academic Press, -NELSON, G„ 1978. From Candolle Io Croizat: London: 1-28. -210- -PITMAN, W. C. III. R. L. LARSON 8. E. M. HERRON. 1974. The ege oT the ocean basins: Two charts and a summary statemant. Geo!. Soc. America, Boulder : 4pp. -PLATNICK, N. I.. 1981. The progression rule or progress beyond rules in biogeography. In: G. Nelson 8i D. E. Rosen (eds), Vicariance biogeography: A critique. Columbia University Press, New York: 144-150. -PLATNICK. N. I. 8* V. A. FUNK (eds). 1903. Advances in dadistics, 2: Proc. second meeting Willi Hennig Soc. Columbia Press, New York : 218pp. -VAN DER SPOEL, S.. 1983. Patterns in plankton distribution and relation Io spéciation: The dawn or pelagic biogeography. In: R. W. Sims. J. H. Price & P. E. S. Whailey (eds), Evolution, lime and space: The emergence of the biosphere. Academic Press, London: 291-334. -VAN DER SPOEL, S. & R. P. WYMAN. 1983. A comparative atlas of zooplankton, Springer- Verlag, Berlin : 168pp. -WILEY, E. 0., 1981. Phylogenetics: The theory and proclive oT phylogenetic systematics, John Wiley 8i Sons. New York : 439pp. -219- TRANSITION ZONES AND FAUNAL BOUNDARIES IN RELATIONSHIP TO PHYSICAL PROPERTIES OF THE OCEAN DONALD B. OLSON Rosenstiel School of Marine and Atmospheric Science. University of Miami, U.S.A. INTRODUCTION western Africa which is a pattern found in many faunal forms around the globe. The range of Transition zones are defined in the physical G.ruber (fig. lb) overlaps the transition zone oceanographic literature to be the areas with to the center of the compositional maximum of mixed water mass properties typically associated G inflata. Subpolar species such as G.pachy- with boundary current extensions and the derma (nut shown) 8re similarly found in this boundary between the subtropical gyres and the zone but with a compositional shift to the south. high latitude circulation systems. In both the The cosmopolitan G.glutinata (Fig. lc) is spread physical and biological usage these are finite areas from the subarctic to the subantarctic but shows a usually differentiated by some hydrographic maximum in its contribution to the total foram- definition. For example, the North American Slope inifer a abundance along the Brazil coast and at the Water represents a transition zone bound by the northern edge of the transition zone as it extends 15*C isotherm contour at the 200m surface and across the southern ocean. the edge of the continental shelf. Biologically, The influence of the physical environment upon transition zones can be delimited by the range of the distribution of life in the world ocean can be so-called "transition zone” species and an add- explored by either carefully mapping the mixture of organisms from both the biogeographic distribution of organisms and physical properties regions bounding the zone. Therefore, translation throughout the ocean, or by outlining the extent of zones are regions .Lntified hy an admixture of the regions providing the correct physical and properties in both a biological and physical sense. biological conditions for the existence of a species. They aiso contain unique elements In terms of The first route of drawing an empirical picture of endemic species and in the intense fronts and eddy the link between the physical environnment and fields associated with them. the geographical distribution of phytoplankton, An example of a transition zone in the South zooplankton, and nekton is limited by a sampling Atlantic and southern Indian Oceans œ seen in the problem, l.e., the distributions of species within distribution of planktonic foraminifera is given in the sea in relation to the physical features of the figure I. The distributions of a transition zone ocean circulation are not well enough known to get species, Globorotalia inflata (fig. la) ; a a very complete picture. The alternate approach of subtropical species, Globigerinoides ruber determining the physical constraints on the (Fig ib); and a cosmopolitan species, Globi biology based on a catalog of physical aspects of gerinita glutinata, (Fig. 1c) taken from the the situation and our knowledge of the influence work of Bé and Tolderlund ( 1971 ) are shown. they have on organisms is aiso severely limited by Distributions ara presented in terms of the geps in our understanding of the marine ecosystem abundance relative to the total foraminifera and the physiology of most marine organisms. In population. The transition zone across the south the distributions in figure 1 and most works ern edge of the subtropical gyres in these oceans dividing the ocean into biogeographic provinces, a Is centered around the extensions of the Brazil and combined approach is used; faunal zones ara Agulhas currents. The transitional species extend delineated along sections but physical properties equatorward into the upwelling regime off south -221- of the environment ere used to extrapolate over large areas. DISfRIBUTION OF PROPERTIES ACROSS TRANSITION ZONES Transition zones represent regions with strong latitudinal changes in water mass properties. Typically this involves a poleward decrease in the temperature (approx. 10*0 in 1000km) and salinity (0.5 to 2.0 parts per thousand in Fig. 2 The concentration of nitrate at a depth of 1000km) with an inverse trend towards higher 100m from the Atlantic GEOSECS data set. Dots nutrient levels in higher latitudes as shown in denote the concentrations on the section down the figure 2 for the Atlantic. The frontal boundaries western basin while the crosses indicate values aiso lead to large contrasts in the depths of the for the legs in the eastern side of the Atlantic. mixed layer and its seasonal cycle. This in combination with enhanced vertical exchange of nutrients in frontal zones and the large-scale level of dispersal in any species depend both on gradients in the nutrient distributions produces the level of change the organisms can tolerate and high variability in the abundance and species the strength of the eddy exchange processes composition of phytoplankton in these areas. associated with transition zones and the fronts The spatial gradients in the phytoplankton found in them. This leads us to study the sugjest very sharp boundaries across currents char,acteristics of the circulation in transition such 83 the Gulf Stream and the fronts associated zones and the unique horizontal and vertical with strong eddy features. For an example of this mixing typical of these regions. contrast the reader may look at the CZCS (Coastal Zone Color Scanner) images of near surface chlorophyll in Brown et al. ( 1985). ADVECTION/DIFFUSION ANO TRANSITION ZONES The contrasts in horizontal structure of phyto plankton communities along with variations in In addition to direct responses of organisms to temperature and salinity across frontal zones lead environmental factors such as temperature, to large variations in higher trophic levels. The salinity, oxygen and nutrient distributions, the sharpness of faunal boundaries in the zooplankton inherent motion of water in the world ocean leads and nekton depend upon the ability of organisms to to a unique environment. The ocean circulation is withstand changes in physical and biological a dominant factor in the determination of pelagic parameters of their environment. In general, distributions. Advection of planktonic organisms organisms with higher tolerances to variations in by the large-scale ocean circulation coupled with their environment will be dispersed more widely diffusion by turbulent eddy fields plays a role in across frontal zones than those less able to the establishment of both the reproductive and withstand these stresses. A similar pattern is seen total range of most species. To consider the within many species in relation to age, with the influence of advection/diffusion on biogeography adults having a larger distribution in space than compare the mean circulation and eddy field in the viable reproductive range of the species. The figure 3 with the distribution of Foraminifera in Fig. I The distribution of three species of foraminifera in the South Atlantic and southern Indian Oceen taken from Be & Tolderlund (1971). Contours are of percent abundance relative to the total forams in the upper 30m of the water column, a) Globorotalia inflata/ b) Globigerinoides rubor, c) Globigerinita glutinata. 222- Fig. 3 Dynamic height (a) and eddy available potential energy (APE) (b) for the South Atlantic and Southern Indian Oceans calculated from the U.S. Navy MOODS historical data set with a two-layer diagnostic model. For a detailed description of the computations see Olson et al. ( 1985) figurai. Although the connection between the two basins is The mean dynamic height field for the surface not well represented in figure 3( a) due to the grid relative to 2000dbar (Fig. 3a) shows the flow in spacing and the limitations of the calculation, a the subtropical gyres of the South Atlantic and portion of the eastward flow in the South Atlantic southern Indian Oceans. Comparison with the continues to add to the flow across the southern distribution of the transition species, (Elabo edge of the subtropical gyre in the Indian Ocean. rata!ia inflata, in figure 1(a) shows the area Therefore, the zonal pattern in Û. inflatus where this for am composes over 20* of the distribution is centered on a consistent flow to the population; the distribution follows the eastward east throughout these basins. This brings forth a flows across the poleward edge of both gyres. question: How does this species maintain itself in a -223- unidirectional zonal flow? There must be some are one case of this type of feature. These eddies mechanism to recruit individuals to the upstream have their own inherent capability to drift to the area off South America in order to maintain the west. In the situation where the flow around the population against advection. ring or eddy is larger than its translation they can It Is apparent from the dynamic height field that carry fluid with them 8s they move. In some parts this recruitment is not taking place to any major of transition zones then, the eddy field may play degree in the mean circulation around the gyre. an important role in recruiting individuals The extension of high relative abundance in the upstream against the mean flow. This can occur in Benguela Current off the east coast of southern the case of Oulf Stream rings, for example (Ring Africa follows the mean flow but suggests this Group, 1981); although, the evolution of the ring extension of the pattern is a net loss to the mean Itself in time may limit the effectiveness of this population, since the species disappears as one process. Typically, the ring become effective proceeds northward along the dynamic height transport mechanisms only for those few species contours. In contrast, the cosmopolitan and which have the ability to exploit the ring subtropical species shown in figurel(b.c) environment (Wiebe& Flierl, 1983). mirror the circulation in the gyre in terms of the Western boundary current systems aiso have 8reas where they make their maximum closed recirculations of quasi-stationary nature contribution. The highest percentage composition associated with them. The best described of these of both of these species are found in the restricted is the Gulf Stream recirculation in the western closed portions of the South Atlantic gyre along the North Atlantic. Thi3 feature io nearly a quarter South American coast. the size of the entire subtropical gyre and A second correlation between the characteristics therefore hss a fairly long recirculation time, of the large-scale circulation and the approximately six months to a year. This system biogeographic distribution of transition species is correlates with a relative abundance maximum in seen by comparison of figure 1(a) and figure 0. glut mata similar to the one observed off 3(b). The zone of highest relative abundance in Brazil in figure 1(c). A pair of recirculation cells 0. inflata corresponds closely to a band of high are reported off the coast of Brazil by Tsychiya eddy energy across the poleward edge of the ( 1985). The highest percentage of abundance for subtropical gyres. The eddy available potential 0.glutinata overlay the southern of these two energy Is a measure of the intensity of the recirculations. mesoscale (50 to 200km scale) eddy field.These The western extreme for the transition species, components of the eddy field lead to temporal O/oboroia/ia inflata, occurs in proximity to variations on a time scale of two weeks to several the region where the Brazil/Falklands (Malvinas) months. The zones of high eddy energy such as that confluence loops offshore. The trajectories of across the basins in figure 3(b) are areas with satellite tracked ARGOS drifters deployed in the high horizontal diffusion as well es vertical confluence and upstream in the Brazil Current exchange. These eddy-induced effects in from October/November 1984 to June 1985 are combination with lateral variations in other shown in figure 4. These pseudo-Lagrangian environmental parameters such 8s nutrients (Fig. instruments provide a crude measure of the drift 2), and some rather special processes occurring patterns expected in the plankton community. in nonlinear features of the eddy field discussed Over the nine months deployment period ali but below, mako the transition zone a unique two of the drifters were swept through the environment. confluence region and out into the eastward flow across the southern edge of the gyre. Many of the trajectories, however, show a region of prolonged COHERENT EDDIES, RECIRCULATION, AND FRONTS residence time thus indicating a partially trapped region in the flow centered at approximately 39*S As part of the eddy field there exist features which and 49*W. Drifters are retained in the can persist for substantial periods of lime. Rings 78,000km2 area approximated by the circle in -224- generally enhanced primary productivity in fronts for the reasons outlined above. Zooplankton and micronekton which maintain themselves in prescribed portions of the water column in the vertical, but restrict themselves to random motions in the horizontal, will be concentrated by the horizontal convergence tied to the existence of near surface fronts (Olson & Backus, 1985). Free swimming nekton may move themselves into fronts Io make use of the higher concentrations of food. These positive aspects of the interaction between biological processes and the flow environment in fronts must be balanced against the problem of recruitment to the front In the face of net downstream advection, as discussed previously, and the stress induced by large change in physical and biological conditions tied to the Fig. 4 Trajectories of nine ARGOS surface drifters environmental contrast across the front and the deployed off South America from October/ vigorous mixing in the frontal zone. November 1984 to June 1985. Circle denotes a region over which the residence time calculation discussed in the text was done. Dots indicate the launch points for the drifters. DISCUSSION AND CONCLUSIONS figure 4 for an average of 3.8 months with two Transition zones are areas where the nature of the units remaining in the region over six months. large-scale ocean circulation and mesoscale This sort of maintenance in the region upstream of features in the oceans' physical structure interact the broad flow extending across the gyre has with biological factors to produce a unique sufficient residence time scales to provide environment. The contrasts in the environment contineous recruitment of individuals to the broad between regions bounding transition zones and the abundance maximum seen in species such æ vigorous eddy fields found In these regions lead to 0. inflata. The effectiveness of recirculation an admixture of fauna whose major distribution is regions such as the one off Argentina in either cosmopolitan, subpolar, or subtropical. maintaining a population against a steady loss due Transition zones aiso have associated endemic to mean advection depends on the reproduction forms which must overcome the net advective loss rate of the organisms compared to their residence due to the unidirectional mean circulation in these time in a region. As the generation time of the zones in order to exist. This mery be accomplished organism increases, a longer residence time In the by a combination of reliance on the mesoscale eddy recirculation is needed to sustain the population field or an ability in adults to withstand long against the net advective loss. periods in transit around the gyres. Tight A final physical phenomenon which is associated recirculations close to the western boundaries with transition zones is frontal activity. The focus may play an important role in recruitment of of much of the discussion ebove has been the organisms into the upstream portions of the mean so-called subtropical front across the South eastward flows. Fronts and an intensified meso Atlantic and southern Indian Oceans. This front is scale eddy field associated with transition zones the core of the eastward transport and is are important in determining the distribution of responsible for the high eddy energy in this animals and phytoplankton. The nature of fronts 8s region. Fronts have important effects on oceen life boundaries between water masses and the from phytoplankton to large nekton. There is enhancement of mixing along them leads to -225- enhanced productivity and iiigher species diversity in their proximity. ACKNOWLEDGEMENTS The author would like to thank R. H. Backus Tor convincing him to attend the meeting. S. B. Hooker, 0. B. Brown, G. Podesta and R. H. Evans contributed to the effort through discussions and a review of the text. This work is supported by ONR (N0014-80-C0042) and(N0014-85-C0020), NSF (OCE 8016991, and NASA ( NAGW-273). REFERENCES -Bf, A. W. H. & 0. S. TOLDERLUND. 1971. Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian Oceans. In: B. M. Funnel) & W. R. Riedel (Eds), Ute micro- paleontology of oceans. Cambridge Press : 105-149. -BRWN. 0. B.. R. H. EVANS, J. W. BROWN. H. R. GORDON. R. C. SMITH & K. S. BAKER, 1985. Blooming off the U. S. East Coast: A Satellite description. Science. 229: 263-167. -OLSON. D. B. & R. H. BACKUS. 1985. The concen trating of organisms at fronts: A cold-water fish and a warm-core Gulf Stream ring. J. mar. Res., 43\ 113-137. -aSON. D. B.. R. W. SCHMITT. M. KENELLY & T. M. JOYCE, 1985. A two-layer diagnostic model of the long-term physical evolution of warm-core ring 82B. J. Geophys. Ros.. 90: 8813-8822. -RING GROUP, 1981. Gulf Stream cold-core rings: Their physics, chemistry, and biology. Science, 212: 1092-1100. -TSUCHIYA, M.. 1985. Evidence of a double-cell subtropical gyre in the South Atlantic Ocean. J. mar. Res., -43: 57-65. -WIEBE. P. H. & G. R. FLIERL, 1983. Euphausia invasion/dispersal in Gulf Stream cold-core rings. Aust. J. mar. freshw. Res., 34\ 625-652. -226- DISTRIBUTION OF MESOBENTHOPELAGIC FISHES IN SLOPE WATERS AND AROUND SUBMARINE RISES NIKOLAY V. PARIN P.P.Shirshov Institute of Oceanology, Moscow, U.S.S.R. INTRODUCTION result in the great diversity of their overall distributions in the ocean. Not unlike the vest majority of biogeographers This approach allows us to recognize species who have tried to explain peculiarities in spatial groups with similar bases of ranges (which can be distribution of the open-ocean pelagic organisms, called “geogrephic elements of the fauna and I consider the present-day distributional ranges flora"; ecologically, they are "recurrent groups") of the individual species as conditioned mainly by and use them for the biogeographic division of the contemporary rather than historic causes. ocean. The majority of ranges of relatively Recognition that correlations between the distrib abundant mesopelagic planktonic fishes (as well utions of plankton ( i.e. ali organisms passively es invertebrates), may be reduced to drifting horizontally together with their con comparatively few main distribution types tinuously moving medium) and water masses exist (Beklemishev et al., 1977; Parin, 1984). At the has teen of utmost Importance in open ocean same time it should be mentioned that the ranges biogeogrephy. This approach applied for the first of some species do not fit such schemes (Parin & time by Heffner (1952) and elaborated by Bekker, 1981 ) and it is possible that the bases of Brinton ( 1962), Ebeling ( 1962) and many other their ranges are localized within the vertical authors, has served as a base of the well-known circulation, es has been suggested by Bruun theory (the so-called "water mass hypothesis") (1958). concerning the association of the distributional The foregoing discussion relates only to limits of planktonic organisms with water mass open-oceen pelagic plankton species (including boundaries. mecroplanktonic fishes), distributed in the midwater environment and without any connection with the bottom and continental shores. It is DISCUSSION known, however, that some species of what are essentially mesopelagic fish genera (aiso Among my compatriots, the late Prof. C. W. belonging to the macroplankton, or micronekton), Beklemishev (1928-1983) mode the most live in slope waters and around submarine rises valuable contribution to this particular field: he and by their habit, may be defined as elaborated in detail the concept of functional bentho-pelagic forms in a broad sense (Parin & structure of distributional ranges for planktonic Oolovan, 1976). These Include permanent organisms in a moving environment, recognizing a near-bottom dwellers, as well as species that "reproductive base(3) of the range" of the migrate vertically to far above the bottom at species, located within a more or less closed night. The following examples may be tentatively horizontal circulation(s), and both non-sterile given: Triplophos hem ingi ( Gonostomatidae), and sterile expatriation areas resulting from Polymetme spp., Yarrella black ford. expatriating currents (Beklemishev, 1969). The (Photichthyidae), Thorophos spp., Mauro extent of those expatriation 8re8s is determined licus muelleri, Argyripnus spp., by differing limiting factors including temper Polyipnus spp., (Sternoptychidae), Odonto ature, dissolved oxygen, biological productivity, stomias spp. (Melanostomiatidae), Idio etc. The variable tolerance to these factors among lychnus urolampus, Diaphus adenomus, species having the same base(s) of range mar/ D. watasei, D. suborbital is, Lampanyctodes -227- hectoris (Myctophidae), Melamphaes acan and descends nearly to the slope over dawn (Fig. thomus, M. suborbitalis (Melamphaeidae), 1 ). Despite passing through strong (to 2.5 knots) Paroneirodes glomerulosus ( Diceratiidae), and contrarily-directed currents during vertical etc. (see aiso Merrett, 1986). A similor mode of migration, these fishes apparently always remain existence is typical aiso for some neklonlc fishes aggregated over the seamount, none having being which are not considered in this report. caught at a distance of 2-3 miles from it. Ali the aforementioned benthopelagic macro- 1 consider this as unequivocal evidence of the planktonic fish species are members of the existence of navigator orientation behaviour, the "open-ocean" families widely distributed in the mechanism of which remains to be understood; it mesopelagic habitat: related species dominating in is evident, however, that the visual reception of these families are characteristic for the open the bottom is excluded. Therefore it is speculated ocean. It seems impossible to explain the that schools of D. suborbitalis are able to distribution of bentho-pelagic fishes from the determine rather exactly their position in point of view of the water mass hypothesis. In midwater relative to the site of their daytime fact, the suggestion of a connection between the residence and can actively counteract reproductive bases of their ranges and the transportation out of the normal species habitat. stationary and quasi-stationary neer-shore and Other bentho-pelagic macroplanktonic species island circulations does not fit with the almost that undergo diel vertical migrations seem to stay complete absence of any considerable expatriation over the slope and near submarine rises in a of such species into the adjacent open ocean (as should be observed according to the above- mentioned concepts). Like their oceanic relatives ali these fishes have pelagic eggs and larvae. Nevertheless, even the dispersion of early developmental stages appears to be very limited since they have been recorded in the open ocean extremely rarely. The eggs of Maurolicus muelleri, which are widely distributed in some areas of the Northern Atlantic (Serebryakov et al., 1983), are thought to be the most important exception. On the other hand, the early stages of slope dwelling myctophids and stomiatoids are very rare in the open sea. Therefore a more appropriate theory should be looked for to explain the existing distribution of bentho- pelagic fishes. In my research I have drawn my attention to - . DAY isolated maintaining populations of bentho-pelagic fishes dwelling on separate seamounts. The rather large population of a myctophld, Diaphus sub orbitalis, inhabiting the Equator Seamount in the western tropical Indian Ocean (0‘26'N, 56*01'E) can be regarded as one of the most Depth(m) striking examples of this kind (Parin & Prutko, 1985). As with the majority of other Myctophidae this species shows diel vertical migration (Qo, 1980). Fig. 1 A scheme shewing diel vertical migrations During these migrations, as confirmed by of the myctophi fish, Diaphus suborbitalis echograms, the Equator population rises to a over the Equator Seemount in the western Indien 50-100m distance above the seamount at night Ocean. -220- similor way. Study of the imitation model macroplankton (strictly, only to micronekton), elaborated by Rudyakov & Tseitlin ( 1985) of an and not to mesoplankton. independent fish population dwelling above a Finally, I wish to draw attention to the great aeemount has shown that such a population is able similarity between the geographic ranges of to be maintained and reproduce even when early bentho-pelagic macroplanktonic fishes dwelling developmental stages are dispersed by turbulent above the slopes and rises and those of nek tonic diffusion. In this case large numbers of larvae fishes inhabiting the same habitats. On the whole, should be found downstream of the mount. This is the general types of distribution patterns typical not the case for the Equator larval population of for such fishes as mentioned above have nothing to D.suborbitalis. Development of these meso- do with the types of patterns typical for open- planktonic ontogenetic stages appears to proceed ocean species. However, the pattern for both directly over the slope and rises but how they are groups of benthopelaglc fishes fit quite well the contained within the nearshore environment division of the world ocean patterned according to remains unclear. However, local gyres (hori the distribution of the shelf and neritic fauna. zontal and/or vertical) of any spatial scale may exist - ones not stationary, but ones possessing a temporary stability commensurate with the ACKNOWLEDGEMENTS duration of development time from egg stage to the actively orientated juvenile stage. I am grateful to Ken Sulak end Julian Badcock for the helpful comments on the manuscript. CONCLUSION REFERENCES Therefore, one can conclude that two princlpial differences exist between closely-related, -BEKLEMISHEV, C. W„ 1969. Ecology and biogeo ecologically and behaviourly similar pseudoceanic graphy oT the open ocean. Moscow, Nauka : bentho-pelagic end oceanic pelagic macro- 191pp. (in Russian). planktonic fishes. The first difference consists of -BEKLEMISHEV. C. W.. N. V. PARIN & 6. I. SEMINA, an absence of considerable dispersion of meso- 1977. Biogeography of Ule ocean. I. Pelagic zone. In: planktonic developmental stages for pseud- M. E. Vinogradov (ad.). Oceanology. Biology of the ocean. Moscow. Nauka : 219 - 261 (in Russian). oceenic forms: the previously suggested hypo -BRINTON, E., 1962. Th« distribution of Pacific thesis which tries to explain this difference by euphausilds. Bull. Scripps Inst. Oceanogr., 8 rapid development of early stages in local gyres is (2): 51-270. not based on reliable facts but some parallels coi -BRUUN, A. F., 1950. On the restricted distribution of be drawn with the situation in upwelling systems two deep-sea fishes, Borophryne apogon and Stomias (Peterson et al., 1979). As far 8S the second colubrinus../ mar. Res., f7{28): 103-112. difference Is concerned (the absence of ex -EBELING, A. W„ 1962. Melamphaidae. 1. Systematica patriation of adults of bentho-pelagic species into and zoogeography of the species In the bathypelagic the open sea), my explanation of this phenomenon fish genus Melamphaes Gunther. Dana Rep., 58 : by the active selfholding in the habitat appears to 164 pp. be more well-founded. -GO, V. B., 1980. Horizontal distribution and diel Moreover, this explanation allows the migration of a mesopelagic microneklonlc fish, Diaphus suborbitalis, in Suruga Bay, Japan. J. conjecture that some oceanic pelagic species 83 Oceanogr. Soc. Korea, 15(2) : 79-00. well, are not always object to simple passive drift -HAFFNER, R. E., 1952. Zoogeography of the In water circulations, but rather can actively bathypelagic fish, Chauliodus. Syst. Zoo!., / (3): maintain their position within a certain pert of 113-133. the habitat. I realize that this conclusion contra -MERRETT, N. R„ 1986. Biogeography and the oceanic dicting my earlier views Is paradoxical, but it Is rim: a poorly known zone of ichthyofaunal interaction. nonetheless quite applicable, if only to In this volume. -229- -PARIN, N. V., 1984. Oceanic ichthyogeogrephy: an attempt Io review the distribution and origin of pelagic and bottom fishes outside continental shelves and nerii!c zones. Arch. Fisch. Wiss., J5: 5-41. -PARIN, N. V. 8, V. E. BEKKER, 1981. Some peculiar ities of geographical distribution of the Pacific Ocean mesopelagic fishes (as exemplified by the Mycto phidae). In: N.6. Vinogradova (ed.), Biology of the Pacific depths. Vladivostok: Far East Science Center, USSR Acad. Sei. : 63-71 (In Russian). -PARIN, N. V.8. G. A. GOLOVAN, 1976. Pelagic deep- sea fishes of the families characteristic of the open ocean collected over the continental slope off West Africa. Trans. P.P. Shirshov fnst. OceanoT, W4\ 250-276 (in Russian). -PARIN. N. V. 3. V. G. PRUTKO, 1985. Thalassa! mesobenthopelagic ichthyocoene above the Equator Seamount in the western tropical Indian Ocean. Okeanologiya, 25{6): 1056-1059 (in Russian). -PETERSON. W. J., C. B. MILLER 6, A. HUTCHINSON. 1979. Zorslion and maintenance of copepod populations in the Oregon upwelling zone. Deep-Sea Pes.. 26A : 467-494. -RUDYAKOV, Y. A. 8. V. B. TSEITLIN, 1985. A simulation study model of an independent fish population from a submarine elevation. Voprosy /kht.. 25: 1031-1034 (in Russian). -SEREBRYAKOV. V. P.. S. S GRIGORIEV 6, V. A. SEDLETSKAYA, 1983. Maurolicus mesleri eggs in the North Atlantic. Northwest Ali. fish. Or g aniz SCR Doc.83! 1X/85, ser .N.751 : 13 pp. -230- TROPHIC FACTORS AFFECTING THE DISTRIBUTION OF SIPHONOPHORES IN THE NORTH ATLANTIC OCEAN P.R.PUGH Institute of Oceanographic Sciences, U.K. INTRODUCTION Judkins ( 1979), was that the faunal change was not always abrupt, even in the region of major In spite of the general lock of consideration given physical boundaries (see Domanski, this volume), to siphonophores and the significant role that they and that there is not necessarily an absolute play in marine ecosystems, there is a reesonable response by an individual species to a change in amount of information on their geographical water mass. Other more subtle reasons may be distribution in the World's oceans, particularly affecting the distribution of pelagic organisms. for the North Atlantic. Much of the earlier date This possibility is examined in relation to the has been summarized by Margulis (e.g. 1972), distribution of siphonophores in the N.E. Atlantic, who drew up distributional maps of 'total ranges', using data from ten stations located between the end broadly divided the species into boreal, equator and 60°N. tropical and equatorial forms. The patterns of distribution were considered to be consistent with those established for other planktonic/nektonic DISTRIBUTION PATTERNS organisms and were related to the basic division of the oceans into various water masses. However, Certain underlying trends appear from these data, these ‘total range' maps give no information on for example.- regional differences in the relative abundance of 1. Species diversity is highest in the warmer, an individual species, nor do they take into more southerly waters around 18°N (Fig. 1 ) and account vertical distribution patterns (see Pugh, declines both towards the equator, and more 1977). The latter situation partially was markedly towards the north. This is a general rectified by Margulis (1984), but again the feature for many groups of pelagic organisms. conclusion were based on first and last capture 2. Neither the numerical abundance nor the principles. biomass (displacement volume) of siphonophores Fasham & Angel (1975), using dete on follows the same trend. The data for the 21 most ostrecods, demonstrated that it was necessary to abundant calycophoran species (nectophores consider ali aspects of the regional, vertical and only), show two peaks of numerical abundance, numerical distribution of the various species in one between I1*N and 18*N, and the other order to establish faunal zones. They found that between 40*and50*N(Fig.l). However, biomass such zones, several of which could be present in tends to increase with Increasing latitude and, any W8ter column, were typified by the presence overall, gelatinous organisms are very important of certain species that hod characteristic relative contributors to the total biomass of pelagic numerical abundances, and that it was rare for an organisms at higher latitudes. individual species to be wholly confined to one 3. The great reduction in the number of species zone. Many of these zones could be associated with towards the north is largely accounted for by the hydrographical features, but for others the disappearance of near-surface living forms. These correspondence was not so apparent. A similar species, which can occur in large numbers in conclusion was reached by Pugh (1977) for warm surface waters, mainly belong to the siphonophores, and Fasham & Pox ton ( 1979) for calycophoran families Diphyidae and Abylidae, and decapods. The general conclusion from ali such Diphyes bojani is taken as an example (Fig studies, as succinctly summarized by Haedrich & 2A). In contrast, the Increase in slphonophore -231- feeding on crustaceans especially copepods, and undoubtedly they play an important role in the pelagic ecosystem. Recent studies by Purcell (e.g. 1980; 1981 ) have shown that siphonophores are selective feeders and the preferred diet of an individual species can, in general, be related to certain morphological and behavioural character istics. Morphologically, there appears to be a direct relation between the 3ize of the feeding polyps (gastrozooids) and the size of the prey captured. Behaviourally, although probably as a consequence of the morphology, those species with smaller gastrozooids tend to be more active and rapid swimmers*. There are aiso differences in feeding strategy ( Biggs, 1977). Active swimmers frequently alternated between periods of swimming and 'fishing', and set, often complex, Latitude N tentacular nets to ensnare their prey. Weaker swimmers tend to spend longer periods 'fishing', Fig. 1 The geographical distribution in the N.E. with their tentacles simply hanging down from the Atlantic Ocean (see Fig. 3 Tor exact positions) of stem. These behavioural differences may be the total number of Siphonophora species ( D—Ü) related to the fact that the swimming speed and and the number of specimens m“2 ( 21 commonest activity of crustacean zooplankton generally calycophoran species) (0--0) present in the net increases with size (Mauchline, 1972). Thus, the samples collected in the top 1000m of the water larger siphonophores simply have adopted a 'sit In column. waif strategy since the chances of encountering a suitable, large prey item are increased by the numbers between 40* and 50*N is caused by large latter's greater activity. Similarly, the lesser numbers of a few deep-living species (eg abundance of such prey can be offset against the Rosacea spp. )( Fig 2 B,C) that mainly belong to energy savings resulting from the siphonophore's the calycophoran families Prayidae, Hippopodiidae lack of swimming activity. and Clausophyidae. These deep-living species, The question thus arises ss to whether these although commoner at higher latitudes, generally differences in dietary preference and behaviour, have widespread distributions. for the two sharply distinct Siphonophora The change-over between the geographical assemblages in the warmer and colder waters of distribution and numerical abundance of the the N.E. Atlantic, can be correlated with major calycophoran families of siphonophores can geographical and vertical differences in the be related directly to the regional differences in distribution of their preferred prey? Although, biomass. The near-surface living abylids and unfortunately, a fully comparable data set for diphylds are mainly small, active predators; the potential prey items e g. copepods and ostracods, deeper living families are generally larger and is not yet available, there appears to be some slow moving. Although these major differences in general evidence to support this supposition. the fauna1 assemblage of siphonophores in warmer Within a singio water column there is a general and colder waters can be associated v/ith various trend for the mean body size both of sn individual water masses (Pugh, 1977) , there maybe other species (Bergmanni rule-see Mauchline, 1972) factors that play more important roles. One such factor could be the dietary preferences of the "the discussion here is limited Io the calycophoran individual Siphonophora species. species, as these are the only ones sampled Siphonophores are carnivorous animals, mainly quantitatively by nets - see Pugh (1964). -232- 7406 4ON 20V 7656 30N 23V 7069 IBN 20V 7000 UN 20V 6553 EQUATOR 500 250 250 500 500 250 250 500 500 250 250 500 500 250 250 500 0 - 1--- 1--- ■--- 1--- 1 0- l--- 1---^-!--- 1 0_ J--- I------1 E É S5Q0- 7709 SON 20V 7711 53N 20V 9^91 PS6 6507 44N 13V 9601 42N 17V 1000500 5001000 1000500 5Û01000 0 -, ’--- L ' ‘ B È 1 £500£ I 7406 4ON 20V 7856 3CN 23V 7CQ9 18N 2CV 7000 11N 2CV 8553 EQUATOR 1000500 5001000 1000500 5001000 1000500 500100C 1000500 5001000 1000500 5001000 0 _ I--- 1--- j--- 1--- I Li ■ _ 1 t 0-, 1--- 1--- 1--- 1--- » 0 -, *--- L- ■ ‘ 1 7 £500- & Fig. 2 A The vertica) distribution of Diphyes bojani, by day and night (left and right of ordinate, respectively). Number of anterior nectophores/l04m3, at various localities (see headers) in the warmer waters of the N.E. Atlantic Ocean. No specimens of D. bojani were found north of 40'N. B - C The vertical distribution of Rosacea spp. at various localities In the N.E. Atlantic Ocean. Number of nectophores/l04m3. PSB= Porcupine Seabight ca. 49*30'N, 14*W ; Equator= 0*N, 22*W. The numbers in the headers for each histogram refer to RRS 'Discovery' Station numbers, except for Sta.7000 which is an amalgam of 'Discovery' Sts 6662 and 7824. and of a taxonomic group, particularly crusta volume occurred within the 500-600m depth ceans, to vary inversely with temperature, at range, while ca. 30* of the total numbers were least within the top 700-1000m of that water present at the shallowest depths (40 and 50m) column. Thus, Roe (1972) found, for copepods in sampled. The vertical distribution patterns of the top 1000m of the water column around the siphonophores(Pugh, 1974), and their projected Canary Islands, thai 5758 of the total displacement dietary preferences, fit in well with this general -233- scheme of increasing prey size with depth. The 1979) were markedly different, with large preponderance of small items, e.g. Copepoda and numbers of small species being present at the ostracods (see Angel, 1979) in near-surface former position, whereas overall numbers were warm waters can be linked with the presence very low at the latter. Below 300m depth, the there of small actively swimming siphonophores, population numbers at both stations were very many of which undergo diel vertical migrations similar. These facts can be related to the (Pugh, 1977). At deeper depths the larger mean distribution of hippopodiid siphonophores, for body size, but lesser abundance, of the prey would Purcell (1981) found that the near-surface suit the presence of larger, less active living species, Hippopodius hippopus, fed Siphonophora species, and these do predominate almost exclusively on Ostracoda. Thus, it was not there. surprising to find thai H hippopus was common In order to explain the disappearance of small, at 30*N, but was totally absent at the 44*N site. If shallow-living Siphonophora species at more one can extrapolate these dietary requirements to northerly latitudes on the same bssis it would be the closely related species, of the genus Vogtia, necessary to find a concomitant decrease in small then the deeper depth distribution of these means prey items. Certainly, es with depth, there is a that they could exploite the larger-sized ostracod trend for an increase in the mean body size of a population present at ali latitudes. population in the colder, northerly waters (e.g. However, with regard to the potentially more Grice & Hulsemann, 1965), but in the superficial important prey, copepods, Roe (1984) found layers of sueli waters the situation is complicated that, at 44*N 13‘W, small Ciausocaianus spp. by the moderately large seasonal changes in predominated at four depths, between 100 end temperature. Thus Deevey ( 1960) found that, for 600m, whereas in the Canary Island region these certain copepod species, not only W8S there an species were concentrated at the shallowest depths inverse relation between body size and water and were less abundant (Roe, 1972). Never temperature, but aiso a direct correlation theless, the total number of copepods was far between mean size and the quantity of phyto greater at 44*N than further south, the plankton material available. This might be related enhancement in numbers being particularly to the large seasonal fluctuations in primary marked at the deeper depths sampled, and this productivity, but it Is probable that 8 more could be associated with the increased number of important factor is the seasonal change in the size deeper-living siphonophores found at more distribution snd specific composition of the northerly latitudes. phytoplankton population itself (Holligan & Harbour, 1977). The body size of the herbivore thus being directly related to the mean size of the CONCLUSION available phytoplankton cells. If this relation aiso holds between the siphonophores and their Thus, despite the necessarily superficial nature of potential prey, then one might expect seasonal the comparisons, it is concluded that the size fluctuations in the specific Siphonophora distribution and abundance of the potential prey population, and its numerical abundance, but population at any one locality and depth plays an unfortunately insufficient data are available in important role in determining the structure of the this context. However, the northward spreading of specific Siphonophora assemblage associated with certain shallow-living slphonophorc species it. As Headrich & Judkins ( 1979) concluded, it is during the summer months (unpubl. data) would relatively easy to establish correlations between be consistent with this. variations in the hydrological conditions and the Other data aiso Indicate a marked geographical distributions, both vertically and horizontally, of change in the size distribution end abundance of certain species, but other underlying factors, potential prey. For instance, the ostracod such as trophic relations, may be playing a moro population in the top 300m of the water column at immediate part in controlling these distributions. 30*N 23*W and at 44*N 13*W (Angel 1977; -234- REFERENCES -PUGH. P. R., 1974. The vertical distribution of the siphonophores collected during the SONG Cruise, -ANGEL. M. V., 1977. Studies on Atlantic halocyprid 1965. *J. mar. biof. Ass. U.K., 54: 25-90. ostracods: vertical distributions of the species in the -PUGH, P. R., 1977. Some observations on the top 1000m in the vicinity of 44*N, 13'W. J. mar. vertical migration and geographical distribution of biol. Ass. U.K., 57: 239-252. siphonophores in the warm waters of the North -ANGEL, h. V.. 1979. Studies on Atlantic halocyprid Atlantic Ocean. In : Proc. Symp. on warm water ostracods: their vertical distributions and community zooplankton. Spec. Puhi. NIO (UNESCO) : 362-378. structure in the central gyre region along latitude -PU6H, P. R„ 1984. The diel migrations and 30'N from off Africa Io Bermuda. Prog. distributions within a mesopelagic community in the Oceanogr., S’. 3-124. North East Atlantic. 7. Siphonophores. Prog. -BIGGS. D. C.. 1977. Field studies of Pishing, feeding Oceanogr., /J: 461-489. and digestion in siphonophores. Mar. Behav. -PURCELL. J. E.. 1980. Influence of slphonophore Physio!., 4: 261-274. behavior upon their natural diets: evidence for -DEEVEY, G. B., 1960. Relative effects of temper aggressive mimicry. Science, 209: 1045-1047. ature and food on seasonal variation in length of -PURCELL. J. E.. 1981. Dietary composition and diel marine copepods in some Eastern American and feeding patterns of eplpelagic siphonophores. Mar. Western European Waters. Bull. Bingham Biol., 65: 83-90. Oceanogr. Coi!., 17: 54-86. -ROE. H. S. J.. 1972. The vertical distributions and -GRICE. G. D. & K. HULSEMANN. 1965. Abundance, diurnal migrations of calanoid copepods collected on vertical distribution and taxonomy of calanoid the 50ND Cruise, 1965. 1. The total population and copepods at selected stations In the northeast general discussion. J. mar. biof. Ass. U.K., 52: Atlantic. J. loo!., 146: 213-262. 277-314. -fASHAM. h. J. R. & M. V. ANGEL. 1975. The -ROE, H. S. J., 1984. The diel migrations and relationship of the zoogeographic distributions of the distributions within a mesopelagic community in the planktonic ostracods in the North-east Atlantic to North Atlantic. 4. The copepods. Prog. Oceanogr., water masses. J. mar. bio!. Ass. U.K., 55 : /J: 353-388. 739-75. -fASHAM. M. J. R. & P. FOXTON. 1979. Zonal distrib ution of pelagic Decapoda (Crustacea) in the eastern North Atlantic and its relation to the physical oceanography. J. exp. mar. Biol. Seoi., 57 : 225-253. -HAEORICH. R. L. & D. C. JUDKINS. 1979. Macro zooplankton and Us environment. In : S. van der Spoel 8» A. C. Pierrot-Bults (eds), Zoogeography and diversity in p lenti on. Bunge sei. Publ. Utrecht : 4-20. -N0LU6AN. P. M. 8, D. S. HARBOUR. 1977 .The vertical distribution and succession of phytoplankton in the western English Channel in 1975 and 1976. J. mar. bibi. Ass. U.K., 57: 1075-1093. -MAR6UUS, R. Y., 1972. Factors determining the large-scale distribution of siphonophores of the suborders Physophorae and Calycophorae in the Atlantic Ocean. Oceanol., 12: 420-425. -MAR6ULIS, R. Y , 1984. The dependence of vertical distribution of the Siphonophora of the World Ocean on the boundaries of water layers. Zh. obsch. Bio!., 45 : 472-479. (In Russian). -MAUCHIINE, J., 1972. The biology of balhypelagic organisms, especially Crustacea. Deep-Sea Res., t9. 753-700. -235- ZOOGEOGRAPHY OF THE INDIAN OCEAN ZOOPLANKTON : CONCEPTS AND CONSTRAINTS T.S.5.RA0 & M MADHUPRATAP National Institute of Oceanography, Boo, India INTRODUCTION distributional limits between 28*S and 42*S. There appears to be a decrease in abundance south The Indian Ocean is cut off in the north by the of 10*S for species that occur on either side of the Asiatic land mess. This coupled with the monsoonal supposed boundary, presumably related to the reversal of surface gyres (see Nalr, this volume) demarcation by the front of nutrient-enrichened results in the distribution of physical and waters of the monsoonal gyre from nutrient - chemical properties typifying the northern Indian depleted waters of the subtropical gyre Ocean. Known zooplankton distribution patterns (Vinagradov & Voronina, 1961 ; Timonia 1971 ; and possible zoogeogrephic zonation were Lawson, 1977). reviewed by Reo ( 1979) and in the atlas of Yan der Spoel & Heymen (1983). In the present contribution knowledge of pattern in the distribution of Indian Ocean zooplankton is briefly BETWEEN OCEAN PATTERNS reviewed on a within and between oceen basis. Differences In species composition between oceans (tropical and subtropical) may depend in part on WITHIN OCEAN PATTERNS depth of occurrence. Thus for calanoid copepods there appears to be much higher overlap between There exists little evidence of biogeographic the Atlantic and Indian Oceans for deep-living difference between the Bay of Bengal and the species (9258 overlap between North Atlantic and Arabian sea. This is despite the fact of known Arabian Sea, Qrice & Hulsemann, 1967) than for differences in physical and chemical parameters surface-living oceanic forms ( 60* overlap (Sengupta&Naqvi, !984;Wyrtki, 1973) end in between Atlantic and Indian, 9155 overlap between the strength of the SW monsoon, which is stronger Indian and Pacific). Similar patterns are seen in in the Arabian Sea, (see Nair, this volume). epiplanktonicchaetognathi (Nair & Madhupratap, Despite delimitation of the eastern/western 1984). The differences may be related to the distributional limits of the copepods Labidocera greater effectiveness of the barrier (Africa) pectina and L. rot Unda (Fleminger et al., between the Atlantic and Indian than that of the 1982) in the Andaman See and the apparent barrier (Australasian seaway) between the Indian absence of the cephalopod Onychia carribea in and Pacific Ojeans. tile Arabian Sea (Yan den Spoel & Hey man, Although biomass equitability among calanoid 1983) , present knowledge indicates that theepi- copepod species is higher in the open ocean than in pelagic region of the entire northern Indian Ocean estuarine or neritic situations (Madhupratap, is a single biogeographic unit. 1983), studies on epipelagic calanoid copepods Despite evidence that the hydrochemical front at (Madhupratap & Harida3, in the press) show the 10*S (Wyrtki, 1973) acts 8s a barrier in the dominance of relatively few species in the open case of certain pteropod (Sakthlvel, 1973) and ocean. Dominance is sometimes considered an euphausiid species (Brfnton & Gopalakhrishnan, index of ability to disperse effectively (Briggs, 1973), this is not the case for oceanic 1974). Of the 22 dominant (those consistently chaetognath or ostracod species (Nair & >155 of the total copepod fraction) epipelagic Madhupratap, 1984), which show southern copepod species occurring in the northern Indian -236- Ocean, 13 havecircumglobal distributions and ali range of epiplanklonic Chaetognatha and Ostracoda in the rest are Indo-Pacific. the western tropical Indian Ocean. HydrobioL, 112 : 209-216. -RAO. T. S. S., 1979. Zoogeography of the Indian CONCLUSIONS Ocean. In : S. van der Spoel & A. C. Pierrot-Bulls (eds) Zoogeography and diversity of plankton. Hoisted Press, New York : 254-292. It is obvious from these studies that knowledge of -SAKTHIVEL, M. 1973. Biogeographlcal change in the distribution patterns is limited to species within latitudinal boundary of a bisub tropical pleropod a quite restricted sort of groups, among them Styliola subula (Quoy & Gaimard) In the Indian Ocean. Copepoda, Chaetognatha, Pteropoda and In : B. Zeitschel (ed.). The biology of the Indian Euphausiacea. Even within these groups knowledge Ocean. Springer Verlag, Berlin : 401-404. for most species is typically sketchy, with few -SENGUPTA, R. & S. W. A. NAQVI, 1984. Chemical studies approaching the completeness of that on Oceanography of the Indian Ocean, north of Ute Pontellina^ Fleminger & Hulsemann ( 1974). equator. Deep-Sea Pes. 3t\ 671-706. Much more basic, synoptic systematic work is -TIMONIA A. 6. 1971. The structure of plankton prerequisite to discussion of current and past communities of the Indian Ocean. Mar. Bibi., 9 : 281-289. distribution patterns of 2ooplenkton of the Indian -VAN DER SPOEL, S. & R. P. HEYMAN, 1983. A Ocean. comparative alias of zooplankton. Springer Verlag, Berlin : 186pp. -VINOGRADOV. M. E. k N. M. VORONINA, 1961. REFERENCES Distribution of some widespread species of copepods in the Indian Ocean. Dokl. Akad. Pauk S.S.S.R., -BRIGGS, J. C., 1974. Narine zoogeography. 140 : 219-222. f1c6raw-Hill, New York: 475pp. -WYRTKI, K. 1973. Physical oceanography of the -BRINTON, E. A K. GOPALAKRISHNAN, 1973. The Indian Ocean. In : B.Zeitschel (ed.). The biology of distribution of Indian Ocean euphausiids. In : B. the Indian Ocean. Springer Verlag, Berlin : 18-36. Zeitschel (ed.). The biology of the Indian Ocean. Springer Verlag, Berlin : 357-382. -fLEMINGER. A. &. K. HULSEMANN, 1974. Systematics and distribution of four sibling species comprising the genus Pontellina Dana (Copepoda, Calanoida). Fish. Bull., 72: 63-120. -FLEMINGER, A.. B. H. R. OTHMAN & J. 6. GREENWOOD, 1982. The Labidocera pectinata group : and Indo-West Pacific lineage of copepods with description of two new species. J. Pianii. Pes., 4 : 245-270. -GRICE. 6. 0. 6. K. HULSEMANN, 1967. Bathypelagic calanoid copepods of the western Indian Ocean. Proc. U.S. netn. Mus., : 122-167. -LAWSON, T. J., 1977 : Community Interactions and zoogeography of the Indian Ocean Candaciidae. Mar. Bio/., 43: 71-92. -MADHUPRATAP, M. 1983. Zooplankton standing stock and diversity along an ocean track in the western Indian Ocean. Mahasagar-Bull. natn. Inst. Oceanogr., 16 : 463-467. -MADHUPRATAP. M. i P. HARIDAS, in the press. Epipelagic calanoid copepods of the northern Indian Ocean. Oceanol. Acia 9 : -NAIR, V. R. & M. MADHUPRATAP. 1984. Latitudinal -237- VICARIANCE ICHTHYOGEOGRAPHY OF THE ATLANTIC OCEAN PELAGIAL THEODOR S. RASS P. P. Shirsov Institute of Oceanology, Moscow, U.S.S.R. INTRODUCTION equatorial regions on both sides of the oceens are somewhat different (Rass, 1980). The history of the formation of the Atlantic Ocean The pélagial of the Atlantic Ocean encompasses a makes it possible to reconstruct the origin of greater diversity of climatic zones as compared to different vicarious forms of pelagic ichthyofauna. other oceans (Schott, 1942), 8nd it was formed There have been several stages in the formation of later than that of the Pacific end Indian Oceens. the Atlantic Ocean which determined composition, Especially the epipelagic ichthyofauna, which taxonomic interrelations and geographical strongly reflects the pattern of climate belts, is distribution of the ichthyofauna of this water different from that of other basins ( Fig. 1 ). body. The separation of the American and African continents initiated this formation process. An equally important phenomenon we3 the presence YICARIANCE for a long period, including the Cretaceous, of the Tethys Sea. Settlement In the Atlantic Ocean of The Ichthyofauna of the Atlantic Ocean contains tropical and warm-temperate groups of epipelagic both purely coldwater cryopelagic genera and fish of Indo-West Pacific origin was possible via species in the Arctic and Antarctic, and purely the Tethys, though extinction of these elements equatorial-tropical genera and species Isolated by followed in the Tertiary (Berg, 1955; Briggs, the ichthyofauna of temperate waters. However, 1974). The development of the ichthyofauna was the genera and species which occupy similar strongly influenced by the emergence of the ecological niches in the different regions of the Central American Isthmus separating the Atlantic Ocean can be considered to replace one another, from the Pacific waters and establishing the representing vicarious groups differing texon- present North end Equatorial Atlantic circulations omically. (Herman, 1979). A more recent event was the Vicariance, when used in connection with the glacial age with alternating cooler and warmer geological past, e.g. In relation with the Panama periods, terminating in a recent warming up of Isthmus, is the phylogenetic concept (sensu North Atlantic Arctic waters. Two other vicarient Nelson & Platnick, 1981, but here it is used In events are of significance: the original meaning (sensu Mayr, 1963) and 1. the emergence of the Peninsula of Florida taken to meen an ecological and topological (Miocene) separating the previously continuous replacement. Zoogeographic studies would be more "Carolinian" fauna, deer If terms and concepts be used In their 2. th8 drying-up (3-4 million years ogo) and original meanings. The boundaries of (ecolog subsequent refilling of the Mediterranean leading ically) vicarious, not necessarily taxonomtcally to a relatively recent, impoverished and partly related, forms from adjacent climatic regions endemic Mediterranean fauna. generally overlap and competitive relations ara The epipeltgic fish fauna of the Atlantic Oceon observed with alternating predominance of one or proper is likely to have been formed during the another vicarious species depending on climatic later half of the Tertiary, mainly In Oligocène and gradients and other factors such 8s, for Instance, Miocene times. Unlike the West Pacific ichthyo selective fishing. fauna it contains no Paleocene or Upper Creta The recognition of (ecologically) vicarious ceous relicts. The ichthyofaunas of the tropical- species in the pelagia! is, therefore, of consider- lOOW 80 160 E 130 10-15 10—20 2B- -23B NNW- mJ ■ F 50 -239- able interest from e theoretical es well es e form a series of ecological vicarians from north commercial point of view (Rass & Carré, 1980). to south. Continuing in a southward direction, the Topologically distinguishable are the epipelagic flying fishes (Exocoetus spp., Cypselurus and the mesopelagic, the nerito-pelagic snd the spp.) and the Antarctic sidestripe (Pleuro oceanic-pelagic ichthyofaunas each containing gramma antarcticum) make the series both planktophagous and ichthyophagous species complete. The last species is ecologically similar (Perin, 1968). The basis of ecological vicariance to the polar cod, but its distribution range has not is the similarity of ecological niches mainly yet been studied exhaustively. determined by food habits. The delimitation of the The ranges of some of these planktophagous ranges of vicarious species is due to differences in species are closely related to the ranges of temperatures at which reproduction is still particular pelagic ichthyophagous species. possible. Temperature limits the reproductive Examples are provided by the distribution range range more than the overall range, since fish are of the saithe ( Pollachius virens ) correspond usually more stenobiontic during reproduction ing to that of the herring, by the distribution than during other periods of their life. areas of mass species of tunas ( Thunnus spp.) Distribution related to environmental temper and dolphinfishes ( Coryphaena ) corresponding atures usually parallel latitudinal climatic to those of flying fishes (Exocoetidae) in the regions. Typical spawning temperatures vary tropical. between -2 and +5-6*C for coldwater Arctic and Antarctic species, mainly between + 3 and 9-11 *C for cold-temperate northern boreal and southern YICARIANCE IN NERITIC TAXA notai (cold-temperate waters of the southern hemisphere,SN in Fig 1) species, between 8-IO The borders of vicarious oceanic pelagic species and 15-20*C for tropical and between 21 and are sometimes similar to patterns of neritic 29*C for equatorial species (Rsss, 1977). pelagic planktophagous species in the temperate waters of the western and eastern coasts of the Atlantic boreal and notai zones and to patterns of VICARIANCE IN OCEANIC TAXA the amphi-Atlantic vicarious genera such as bitemperate(antitroplcal) anchovies ( Engraulis Meridional vicariance, always of the ecological spp.) and horse mackerels ( Trachurus spp.) type, can be observed in both oceanic pelagic and Bitemperate genera are represented in waters neritic pelagic species, while amphi-Atlantic of the southern part of the boreal zone by the vicariance, which may aiso be of a phylogenetic North American and European anchovies (/. nature, is traceable only in neritic pelagic species eurystole, and £. encras/colus) and horse separated by open ocean waters. Epipelagic mackerels ( T. lathami, T trachurus) which planktophagous fishes are particularly oceanic are replaced in the corresponding waters of the and frequently show meridional vicariance. For notai zone by South American and South African example, the polar cod ( Boreogadus sarda), the species ( f. anchoita, E. capensis and T. Arctoboreal capoi In (Mallotus villosus), the lathami australis, T. capensis). These species northern boreal Atlantic herring ( Clupea ara meridional ecological vicariants and Harengus harengum, together with the meso amphi-Atlantic ecological es well 8s phylogenetic pelagic planktophagous redfish ( Sebastes vicariants. An excellent example of the marinus), the saury ( Scomberesox seurus), amphi-Atlantic phylogenetic vicariance is and together with the predominantly mesopelagic provided by anadromous shads (Alosa spp.) blue whiting ( Micromesistius poutassou) occurring in the southern part of the boreal Fig. I Climatic-biogeographical regions in the World Ocean and range of their mean monthly temperatures. A - Arctic, NB - northern Boreal, SB - southern Boreal, T - tropical waters, E - equatorial region, NN - northern Notai, SN - southern Notai, ANT - Antarctic. -240- waters off western Europe from the Baltic Sea to sauries, anchovies and horse mackerels must have northern Africa and in the basin of the Medi formed during the Oligocène cooling, diverging terranean Sea (five species) as well æ off North northward and southward of the equstor during the America from the Guii of St.Lawrence to Florida subsequent warming-up of the Equatorial waters (six species.). (Berg, 1933; Hubbs, 1952). For this In the western coastal waters of the Atlantic phenomenon it is therefore not evident which kind Ocean the species Brevoortia tyrannus, of vicarians is concerned. The West Atlantic B. patronus, B. smithi, B. au rea and B. menhaden species and East Atlantic species of pectinataof menhaden are meridional ecological pilchard and sprat are aiso likely to hove become vicarients. In the eastern coastal waters of the separated in Oligocène and early Miocene time. The Atlantic Oceen meridional ecologically vicarious anadromous shads must have moved from esst to distributions are distinctly shown by several west somewhat later, probably in early clupeoids: sprat ( Sprattus Sprattus ) in the Pleistocene time. Not long before the uplift of the European boreal waters proper, pilchard Central American Isthmus, probably in Pliocene ( Sardina pilchardus ) in the southern boreal time, the tropical amphi-American group of zone, sardinella ( Sardinella aurita ) in the Opisthonema, Harengula and Cetengraulis tropical-equatorial waters and South African came into being and supplemented the group of pilchard ( Sardinops ocellata ) in the northern epipelagic species of Decapterus and, possibly, notai waters. Chloroscombrus, which had come with Tethys Of special interest are phylogenetic vicarious waters. And, finally, the most recent ættlers in interrelations between the pelagic ichthyofauna of the Atlantic Oceen waters, probab.y as recent as the Atlantic Ocean and the Paciae Ocean Holocene, are a group of several genera of ichthyofauna (Ekman, 1953; Rosenblatt, 1967) Indo-West Pacific genesis - Exocoetidae, In origin these species result from geographic Sardinella and Sardinops. isolation, bu’ as we are dealing here with a geological phenomenon affecting a whole fauna and different taxonomic groups, it should be ACKNOWLEDGEMENT considered a vicariance event. Examples of am phi-Amer icon vicarious relations are found in I thank Dr. K. J. Sulak for his valuable comments clupeoids ( Opisthonema oglinum, and und correction of the English version of the 0. libertate, Harengula spp. and H manuscript. thrissina), anchovetas ( Cetengraulis eden tulus and C. mysticetus ) and carangids ( Chloroscombrus chrysurus and C. REFERENCES or quote, Decapterus macarellus and D. scombrinus ) -BERG, L. S., 1933. Die bipolare Verbrellung der Organismen und die Elszelt. Zoogeogr., / (N 4); 444-484. CONCLUSIONS -BER6, L. S., 19SS. Classification or fishes both recent end fossil (2-nd ed). Tray. Inst. Zool. The arctoboreal capelin is represented in the Acad. Sei., U.R.S.S., 20\ 1-286 (In Russi™). -BRIGGS, J. C.. 1974. Marine Zoogeography. Atlantic and Pacific Oceans by different McGraw. HUI, New York : 475 pp. subspecies, probably separated by glaciation in -EKMAN, S., 1953. Zoogeography at the Sea. Pleistocene time. The northern boreal Atlantic Sedgewick & Jackson, London: 418 pp. herring was represented in the Eocene by related -HUBBS, C. L., 1952. Antftropical distribution of species in Europe and must have generated the fishes and other organisms. Seventh Pacif. Sei. related White Sea - Pacific herring ( epa!Iasi ) Congr., J : 324-329. in the Miocene. -MAYR, R., 1963. Animal species ana The bitemperate subspecies and species of evolution. Bellknap Press Harvard Univ. Press, -241- Cambridgn, Mass: 797 pp. -NELSON, 6. 8, N. PLATNICK, 1981. Systematica and biogeography: ciadistics and vicariance. Columbia Univ. Press, New York: 567pp. -PARIN. N V.. 1968. ichthyofauna or the oceanic pelagia!. Moscow, Nauka: 186 pp. (in Russian). -RASS, T. S.. 1977. Geographical regularities in re production and development of fishes in different climatic zones. Proc. Shirshov Inst. Ocaanoi., i09\l-A\ (inRussian). -RASS, T. S., 1980. Symmetry and asymmetry of ichthyofauna of the Ocean. Oceanology a (U.S.S.R.), 20 (N 5) : 783-791 (in Russian). -RASS, T. S. &> F. CARRE. I960. Les Pêches maritimes: complexes biogéographiques de production et provinces halieutiques. Rev. Trav. inst. Pêches marii., dd (2) : 89-117. -ROSENBLATT, R. H., 1967. The zoogeographies! relationships of the marine shore fishes of tropical America. Stud. Trop. Oceanogr., 5 : 579-592. -SCHOTT, G.. 1942. Géographie des Aiian- iischen Oceans. C. Boy sen, Hamburg: 438pp. -242- EPIPELAGIC MEROPLANKTON OF TROPICAL SEAS: ITS ROLE FOR THE BI06E0GRAPHY OF SUBLITTORAL INVERTEBRATE SPECIES RUDOLF S. SCHELTEMA Woods Hole Oceanographic Institution, U.S.A. INTRODUCTION light, sometimes completely uncalcifled, shells (Pechenlk et al., 1984; Richter, 1984). Epipelagic meroplankter3 are the larvae of Cymatiidae have particularly long velar lobes benthic invertebrates that have been carried used for swimming as well as feeding (Fig. 1), end offshore from the continental shelf or the coast of there Is some Indirect evidence In older veliger oceanic islands either by eddy diffusion or larvae for metabolic changes related to their long advective processes. Among the latter may be planktonic existence. Other invertebrate groups included such phenomena as "rings", as with teleplanic larvae aiso show some morph encountered in the Gulf Stream system of the ological modifications seemingly related to a long western North Atlantic (Fileri & Wroblewskl, larval life. 1985) and quaslgeostrophlc mesoscale eddies seen In this account I propose to summarize the off the Hawaiian Islands (Lobel & Robinson, present knowledge about the occurrence of 1983; In the press) that affect dispersa) both meroplankton throughout the tropical waters of toward and away from coastlines. The existence of the world and to discuss briefly the possible invertebrate larvae of benthic species Far out in overall significance of long-distance dispersal. the open oceen has been known sina, the P lepton Only the larvae of prosobrench gastropod molluscs Expedition, the results of which wsre reported iii will bo considered here as an example, since they a series of volumes published near the end of the constitute one of the most frequently occurring last century (polycestus and sipunculana: taxa with teleplanic larvae (Scheltema, in the Hacker, 1898; gastropod and bivalve molluscs: press, Tahia I). Slmroth, 1895; echinoderma: Mortensen, 1898). The possible significance of these early observations apparently was not considered by METHODS biologists at that time, and it was not until the last two decades that systematic investigation of the Data on the occurrence of teleplanic epipelagic meroplankton was undertaken gastropod-veliger lervae were collected in the (Milelkovsky, 1966; Robertson, 1964; tropical Atlantic Ocean over the past twenty years Scheltema, 1964; 1966; 1968; 1971a; b). mostly on ships of the Woods Hoia Oceanographic These studies were largely restricted to the North Institution, incuding R/V ATLANTIS II, R/V and South Atlantic Oceans, from which a variety of CHAIN, R/V KNORR and R/V CRAWFORD and Invertebrate larval types have been described. include 412 lucations. The Pacific Ocean samples Most larvae studied from epipelagic waters retain were obtained by expeditions of the Scrlpps their competence to settle (Scheltema, in the Institution of Oceanography over the pest 26 press), and It Is inferred from such observations years and wera augmented by a cruise of the R/V that teleplanic larvae can delay settlement over ATLANTIS II in 1979 between Wellington, New long periods of time until they encounter an Zealand and Honololu, Hawaii. A total of 337 adequate cue for settlement. locations are represented. Semples from the Teleplanic larvae often show special adaptations tropica] Indian Ocean are from the Lusfad for a long planktonic life. Among gastropods many Expedition I and II taken during 1962 by the R/V species have long periostracal spines and very ARGO of the Scripps Institution of Oceanography -243- Fig. I Teleplanic veliger larva of acymatiid, referred to Cymatium labiosum ( Wood 1928) from the Oulf Stream in the western North Atlantic Oceen. The larval shell may exceed 5mm in length and is dark amber. There is an elaborate pattern of short, soft, periostracal spines giving a hirsute appeerance (see, Scheltema 1971b, Fig. 32 : 21). Cymatium labiosum is known in the western Atlantic from North Carolina to Brazil, the Caribbean, Bermuda and throughout the Indo-Pacific including Hawaii. and included 48 stations. The samples were taken I. This order of abundance is largely the same es by oblique tows from the surface to depths of ca that in the Atlantic and Indian Oceens, though 150 to 200m 8nd were made with nets of either samples from particular expeditions sometimes 3/4 or one meter diameter with a mesh of 240 to showed reversals of the most abundantly 360pm ( usually the former ). encountered families. At least VOX of ali open ocean samples taken in tropical waters contain teleplanic gastropod larvae with the exception of RESULTS the tropical region between 120* and 160*W in the East Pacific. The distribution of veliger larvae of gastropods are figured on maps of the tropical Atlantic, Pacific and Indian Oceens (Figs 2, 3 and 4). DISCUSSION Specifically designated are those locations where larvae belonging to the gastropod families The question arises es to the significance of ali Architectonicidae and Cymatiidae were found. In these larvae so widely distributed in the the initial sorting 18 families of gastropods were epipelagic waters over such large regions of the readily recognized and the rank order of their world's tropical oceans. What role do these larvae occurrence in the Pacific is summarized in Table play in the geographic range of the species? This -244- Fig. 2 Distribution of teleplanic gastropod veliger larvae in the epipelagic of the tropical Atlantic Oceen. Data are from 412 plankton tows. Large circles and triangles indicate localities where veligers were found. The small circles are positions where plankton tows were taken but no gastropod larvae appeared in the sample. Large, filled circles= Architectonicidae; large, open circles* Cymatiidae; divided circle (half-filled and half-open)* stations where both architectonicid and cymatiid veligers were found. Triangles show points where veligers of other coastal benthic gastropod species were found. Arrows indicate major surface circulation. (Distributional data modified from Scheltema, 1978; 1979 with some additional data added.) 140' WO' M0' Tuamotu V -245- eo ôo too r n Fig. 4 Distribution of teleplanic gastropod veliger larvae in the epipelagic of the tropical Indian Ocean. Data from 48 plankton tows. Ali stations included gastropod veliger larvae. Surface current for the month of August shown by arrows were determined during the period when plankton was collected. (Currents generalized from Taft & Knauss, 1967: Fig. 5). Symbols 8S in figure 2. question does not have a simple answer; it is southeastern coast of the United States (Beaufort, necessary to understand not only how species are North Carolina) shows that species with dispersed but aiso what constraints there are for non-planktonic development are with few dispersal, namely the ecological and biogeographic exceptions constrained largely to a limited length barriers that determine where species may of the continental coastline and are ali restricted survive and reproduce. in geographic range to the western Atlantic. No matter where a teleplanic larva is carried by Excepted are three species presumed to have been ocean currents, there are ecologie conditions, viz. introduced to the eastern Atlantic on oysters. In physical and biological attributes of the contrast, those species from the same region environment, that will limit spatial distribution known to have teleplanic veliger larvae ere ali of a species both within and aiso at the limits of shown to have wide latitudinal ranges in the lis geographic range. Bhaud ( 1984) claims that western Atlantic (some over 60*) and 815? are the results of larval dispersal cannot be amphi-Atlantic in their geographic distribution. distinguished from such ecologie constraints. These dete are set forth in more detail elsewhere. Notwithstanding this view, an analysis of the Any consideration of the contemporary warm-tamperata prosobrench fauna of the distribution of species must aiso account for the Fig. 3 Distribution of teleplanic gastropod veliger larvae in the epipelagic of the tropical Pacific Ocean. Data from 337 plankton tows. Arrows show surface circulation generalized from pilot charts. Distributional data for the central Pacific in part from Scheltema (in the press, 1986) with the addition of 127 previously unrepor ted locations. Symbols as In figure 2. -246- Table I Larvae of sublittoral Gastropoda the Tertiary. The Tethys Sea and the passage common in the epipelagic waters of the between North and South America provided a tropical Pacific Ocean (Based on 337 continous circumtropical route by which larvae stations) could have been transported westward between the tropical lodo-Pacific and Atlantic Ocean (Fig. 5). TAXON No. Percent Likewise, the corridor between North end South Stations Occurrence America allowed a connection between the tropical marine faunas of the western Atlantic and eastern Ali Bastropoda 240 71.2 Pacific. The Tethys See closed at its eastern end at Architectonicidae 124 36.8 the beginning of the Ollgbcene (ca. 36 million Naticidae 83 24.6 years ago) thereby separating the tropical Cymatiidae 82 24.3 Indo-Pacific and Atlantic faunas, but there still Neritidae 52 15.4 remains a large number of families and genera of Cypraeidae 37 11.0 molluscs in common between the two regions, Thaididae 29 8.6 reminiscent of a former seaway connection. The Triphoridae 27 8.0 corridor between North and South America closed Coralliophilidae 22 6.5 in the Early Pliocene (ca. 3 million years ago) Bursidae 20 5.9 preventing the possibility of any larval exchange Tonnidae 18 5.3 between these two regions, but the period is short Strombidae 16 4.7 enough so there sini exist some species of •Other 176 52.2 molluscs held in common between the western Atlantic and eastern Pecific. M Includes Cassidae. Columbellidae. Cerithiidae. The mode of development of Tertiary fossil Turridae, Ovulidae, Conidae and Muricidae each prosobranch gastropods can be inferred from the at less than 3X of stations Data from the central Pacific (Scheltema, in the press. Table 2) to which has been added 127 additional samples from the eastern and far western Pacific. dimension of time. Events that affect species distribution mo/ be in the order of decodes, centuries, thousands of years, or over geologic periods of time. Examples are: a) climatic change which affects the latitudinal range of species (e.g., Bousfield & Thomas, 1975 describe changes In the Virginia fauna since the Early Hypsithermal, ca. nine thousand years ego); ./____ b) transgression and regression of sea level ( Vail et al., 1977) which alter the amount of available habitat along coastlines and the number of Fig. 6 The disposition of continents and the "stepping stones" available for dispersal; inferred surface circulation of the World Oceens c) the opening and closing of seaways or corridors during the Cretaceous/Paleocene (65my ago). which can restrict or facilitate the possibility for Arrows show surface circulation. Na= North dispersal (cf. Hallam, 1973); America, Ea= Eurasia, Sa= South America, Af= d) seafloor spreading which over geologic time Africa, ln= India, At= Antarctica, As= Australia. affects the size of ocean basins that act es barriers (After: T. H. Van Andoi, Fig. 12, 1976: 18; data to the dispersal of coastal species. from: Dietz & Holden, 1973, continental The closing of seaways and corridors markedly position; Berggren & Hollister, 1974; Luyend/k affected the possibility of larval dispersal during et al., 1972, circulation pattern). -247- protoconch or larval shell at the apex of and 160*W and suggest that the East Pacific may well-preserved and identifiable juvenile or adult aiso serve ss an efficient filter for dispersal of specimens (Jablonski & Lute, 1983; Scheltema, many gastropod species. 1979; 1981 ; Shuto, 1974). From what is known The Mollusca of central Pacific islands about congeneric or confamlllal forms, It Is aiso represent an attenuated Indo-Pacific fauna and the possible to distinguish which species have endemism, even of the more remote Hawaiian teleplanic larvae. Such knowledge makes infer Islands, is relatively low (ca. 2058 Key, 1979) ences possible about larval dispersal in the compared to terrestrial insects among which some geologic psst. taxa may have 9858 endemism (Carlquist, 1974). Seafloor spreading In the Atlantic during the Owing to the geologic origin of tropical central Tertiary has resulted in the ever-increasing Pacific islands by volcanic activity from the ocean distance between the African continent and Central floor, colonization by sublittoral gastropod and South America to the west. It is estimated that species necessarily must have resulted from long if allowance is made for the higher current distance dispersal (Scheltema & Williams, velocity (Luyendyk et al., 1972) and aiso the 1983). Taxa without larval development smaller size of the Atlantic Basin during the Early generally are absent from Polynesian Islands (e.g. Tertiary (Fallow, 1979; Fallow & Dromgoole, Volutidae, Cancellariidae, etc.). The widespread 1980), the time required to cross from Africa to persistence of Indo-Pacific species on central the Caribbean by a passively drifting larva would Pacific Islands suggests that there Is at least have been between ca. two to four weeks, well intermittent gene flow among island populations within the lenth of the development for most and aiso between them and other regions of the contemporary species with planktotrophic larvae Indo-Pacific. To test such an hypothesis, (Scheltema. 1979). Today the time required is examination of genetic variation of specific substantially greater, between two and six months gastropod species is now required (see: Slatkin, (depending on the current system considered) snd 1985) along with data on the larval dispersal of the Atlantic, because of its now greater width, acts such species. The latter depends on the description as o filter allowing only the passage of some and subsequent identification of the larvae. teleplanic larvae. Ekman ( 1953) proposed that the eastern Pacific acted ss a barrier to larval disperal. ACKNOWLEDGEMENTS Thorson (1961) believed that "under average conditions even long-distance larvae have a much Over the years I was helped at sea in obtaining too short pelagic life to survive the critical samples by my various assistants who have distances across the eastern Pacific..." included John R. Hall, Janet Moller, and Isabelle Zinsmeister & Emerson (1979) discuss the P. Williams. The Pacific and Indian Oceans possibility of larval dispersal across the eastern samples were made available to me by Dr. A. Pacific Barrier and conclude that the relative Fleminger and Mr. George Snyder, and I am' paucity of Indo-West Pacific species of molluscs Indebted to Professor John McGowan for the use of In the eastern Pacific is owing to the "vast laboratory facilities while visiting Scripps expanse of open water" and "lack of suitable Institution of Oceanography. My research habitats with available ecological niches...." Leis associate, Isabelle P. Williams helped in sorting (1984) examined the possibility of larval the Pacific end Indian Oceans samples. This dispersal to explain the high Indo-Pacific element research was supported in part by Grant No. of coral reef fish thai occurs in the east tropical OCE-8410262 from the National Science Pacific (up to 2455), but was unable to arrive at Foundation. a definite conclusion owing largely to insufficient plankton data. The distributional data of archi- tectonicid and cymatfid veliger larvae (Fig. 3) show a decrease in their occurrence between 100* -248- REFERENCES Pacific Barrier. Oceanogr. trop. (ORSTOM), 19: 181-192. -60USFIELD, E. L. & M. L. H. THOMAS. 1975. Post -L08EL, P. S. & A. R. ROBINSON, 1983. Reef fishes at glacial changes in distribution of littoral marina sea: ocean currents and the advection of larvae. In: invertebrates in the Canadian Atlantic Region. Proc. M. L. Reakea (ed.) The ecology of deep ano Nova Scotia Inst. Sei, 77 (Suppl. 3): 47-60. shallow water cora/ reefs. Synoptic Ser. -8ERG6REN. W. A. & C. 0. HOLLISTER. 1974. Undersea Res., NOAA Undersea Res. Program: 29-38. Paleogeography, paleobiogeography, and the history -LOBEL. P. S. & A. R. ROBINSON (In the press). of circulation in the Atlantic Ocean. In: W. W. Hay Transport and entrapment of fish larvae by ocean (ed.) Studies in pa/eo-oceanogr apt)y Soc. Econ. mesoscale eddies and currents in Hawaiian waters. Paleontol. Mineralog., Spec. Pub., 20 : 126-166. Deep-Sea Ros. (1986). -BHAUD. M., 1984. Les larvés meroplanctoniques et -LUYENDYK, B. P.. D. FORSYTH & J. D. PHILLIPS, leur implication el biogéographie paleobiogéographie. 1972. Experimental approach to the paleo-circulalion C. fi. Acad. Sei. Paris 299, Ser. III : 361-364. of the oceanic surface waters. Geo/. Soc. Amor. -CARLQUIST. S.. 1974. Island Biology. Columbia Bull., 83 : 2649-2664. Univ. Press: 660pp. -MILEIKOVSKY, S.A., 1966. The range or dispersal or -0IETZ, R. S. & J. C. HOLDEN. 1973. The breakup of the pelagic larvae of bottom invertebrates by ocean Pangaea. In: Readings from Scientific currents and its distributional role on the example of American. W. H. Freeman. San Francisco : 102-113. Gastropoda and Lamellibranchia. Okeano/ogiya, 6 : -EKMAN, S., 1953. Zoogeography of the Soa. 482-491. (translation: Acad. Sei. USSR Oceanol. Sidgwick and Jackson. London: 417pp. Scripta Technics: 396-404.) -FALLOW, W. C., 1979. Trans-North Atlantic -MORTENSEN, T„ 1898. Die Echlnodermenlarven der similarity among Mesozoic and Cenozoic invertebrates Plankton-Expedition. Frgebn. Plankton-Exped. correlated with widening of the ocean basin. Humboldt St if flung. Il J: 120pp. 6oology, 7 : 398-400. -PECHENIK. J. A.. R. S. SCHELTEMA 8, L. S. EYSTER, -f ALLOW. W. C. & E. L. DROMGOOLE, 1980. Faunal 1984. Growth stasis and limited shell calcification in similarities across the South Atlantic among Mesozoic larvae of Cymatium parthenopeum during and Cenozoic invertebrates correlated with widening trans-Atlantic transport. Science, 244:1097-1099. of ocean basins. J. Seoi., 88 : 723-727. -RICHTER, G„ 1984. Die Gehauseentwicklung bei den -FLIERL, G. R. ê. J. S. WR06LEWSKI. 1985. The Larven der Cymatiiden (Prosobranchia: Tonnacea). possible influence of warm-core Gulf Stream rings Arch. Moll., 115: 125-141. upon shelf water larval fish distribution. U.S. Fish. -ROBERTSON, R„ 1964. Dispersal and wastage of Bull., 83 : 313-330. larva Philippia krebsii (Gastropoda: Architectoni -HACKER, V., 1698. Die pelagischen Polychseten und cidae) in the North Atlantic. Proc. Acad. Sei. Achaelenlarven der Plankton-Expedition. Frgebn. Philadelphia, 115: 1-27. Plankton-Exped. Humboldt-Stiff lung, II, H, d. -SCHELTEMA, R. S„ 1964. Origin and dispersal of 50pp. invertebrate larvae in the north Atlantic. Am. Zoo!., -HALLAM, A., 1973. Distributional patterns in 4: 299-300. contemporary terrestrial and marine animals. In: -SCHELTEMA. R. S„ 1966. Evidence for trans Organisms and continents through time. Spec. Atlantic transport of gastropod larvae belonging to Pap. Paleontol., 12 Syst. Ass. Puhi. 9: 93-/05. the genus Cymatium. Deep-Sea Pes., 13: 83-95. -JABLONSKI, D. J. 8, R. A. LUTZ, 1983. Larval -SCHELTEMA, R. S., 1968. Dispersal or larvae by ecology of marine benthic invertebrates: equatorial ocean currents and its importance to the Paleontological implications. Biol. Rev., 58 : zoogeography of shoal-water tropical species. 21-89. Nature, 217: 1159-1162. -KAY, E. A., 1979. Hawaiian marine shells; -SCHELTEMA. R. S.. 1971a. The dispersal of the reef and shore fauna of Hawaii. 4. Mollusca larvae of shoal-water benthic invertebrate species Bernice P. Bishop Mus. Spec. Puhi. 64(4) Bishop Mus. over long distances by ocean currents. In: D. J. Crisp Press, Honololu, Hawaii: 653pp. (ed.). Fourth European Mar. Biol. Symp. -LAURSEN, D., 1981. Taxonomy and distribution of Cambr. Univ. Press: 7-28. teleplanic prosobranch larvae in the North Atlantic. -SCHELTEMA. R. S., 1971b. Larval dispersal as a Oena Rep., 89: 43pp. means of genetic exchange between geographically -LEIS, J. M.. 1964. Larval fish dispersal and the East separated populations of shallow-water benthic -249- marlne gastropods. Biol. Bull., Woods Hole, tectonics, paleography and paleoceanography. In: J. MO : 284-322. Gray 8» A. J. Boucot (eds). Historical -SCHELTEMA. R. S„ 1978. On the relationship biogeography,' plate tectonics, and the between dispersal of pelagic larvae and the evolution changing environment. Oregon State Univ. Press. oT marine prosobranch gastropods. In: B. Battaglia 8» Corvallis, Oregon: 9-25. J. A. Beardmore (eds). Marine organisme - -ZINSMEISTER, W. J. 8, W. K. EMERSON. 1979. The genetics, ecology and evolution. Plenum Press. role of passive dispersal in the distribution of New York, London: 303-322. hemipelagic invertebrates, with examples from the -SCHELTEMA. R. S.. 1979. Dispersa! or pelagic larvae tropical Pacific Ocean. Veliger, 77:32-40. and the zoogeography of Tertiary marine benthic gastropods. In: J. Gray k A. J. Boucot (eds), Historical biogeography, plate tectonics, and the changing environment. Oregon Slate Univ. Press, Corvallis. Oregon: 391-397. -SCHELTEMA, R. S., 1981. The significance of larval dispersa! to the evolution of benthic marine species. In: V. L. Kosyanov 8. A.I. Pudovkin (eds), Genetics and reproduction of marine organisme. Acad. Sei. U.S.S.R. Vladivostok: 130-145 (Russian with English abstr.). -SCHELTEMA. R. S. 8. I. P. WILLIAMS. 1983. Long-distance dispersal of planktonic larvae and the biogeography and evolution of some Polynesian and western Pacific mollusks. Bull. mar. Sei., JJ : 545-565. -SCHELTEMA, R. S„ (in the press). Long distance dispersal by planktonic larvae of shoal-water benthic invertebrates among central Pacific islands. Bull. mar. Sei. -SHUTO, T., 1974. Larval ecology of prosobranch gastropods and its bearing on biogeography and paleontology. Le thai a, 7\ 239-256. -SIMROTH. H., 1895. Die Gastropoden der Plankton-Expedition. Ergebn. Plankton-Exped. Humboldt Stifftung. /, F.d. 206pp. -SLATKIN, M„ 1965. Gene flow in natural populations. Ann. Rev Eco/. Syst., 16: 393-430. -TAFT. B. A. 8. J. A. KNAUSS. 1967. The equatorial undercurrent of the Indian Ocean as observed by the Lusiad Expedition. Bull. Scripps Inst. Oceanogr. 9: 193pp. -1H0RS0N, G„ 1961. Length of pelagic larval life in marine bottom invertebrates as related to larval transport by ocean currents. In: M. Sears (ed.), Oceanography. Amor. Ass. Adv. Sei., Wash. Puhi. 67: 455-474. -VAIL, P. R.. R. M. MITCHUM, JR. 8, S. THOMPSON III. 1977. Seismic stratigraphy and global changes of sea level, Part 4: Global cycles of relative changes of sea level. In: C.E. Payton (ed.), Seismic stratigraphy - applications to hydrocarbon exploration. Amer. Ass. Petroleum Geo). Mem., 26. : 83-97. -VANANDEL, T. H., 1976. Eclectic overview of plate -250- BIOGEOGRAPHY OF OCEANIC ZOOPLANKTON CHANG-TAI SHIH National Museum of Natural Sciences, Ottawa, Canada INTRODUCTION cosmopolitan or widely distributed species. These morphological forms are designated at some Distribution of marine zooplankton has been taxonomic leve] from geographical forms to discussed in recent years by a number of authors, distinctive species, usually at the discretion of the e.g. Yan der Spoel & Pierrot-Bults ( 1979). The authors. It is interesting to note that the absence of effective geographical barriers and the distribution of these variations exhibits typical paucity of ecological niches in the ocean, as geographical patterns. Yan Soest ( 1975) reported already pointed out by McGowan (1971), end the latitudinal morphological variations in some salp 3low process of allopatric spéciation are account species. Yan der Spoel ( 1967 ; 1976) showed that able for the low number of species in oceanic different formae are usually found in different zooplankton. This paper, by examining the water masses. Shih ( 1986) regarded those distribution of some pairs of morphologically morphological variations which are distributed in similar species, proposes a hypothesis that a similar latitudes in the same or different oceens unique type of spéciation of planktonic anima)3 in as analogous species, referring to their similar the see may sporadically take place in an area morphology and parallel distribution, and gave where stability of oceanic condition is altered by several examples of oceanic copepods. Most the adm ixture of waters from different origins. analogous species are epipelagic and found in equatorial to central waters (Shih, 1979). There ara two types of analogous species: DISTRIBUTION PATTERNS AND ANALOGOUS interoceanic and intraoceenlc. Interoceanic an SPECIES alogous species have each species of the pair living in a different ocean. Usually they are II has long been noted that general distributional distantly separated from each other by a continent patterns of oceanic zooplankton coincide with but sometimes they are olosa. Several pairs of large-scale closed and semiclosed oceanic interoceanic analogous species have one member structures. Beklemishev (1971) and McGowan found in the South Atlantic and another in the (1974), for instance, proposed distributional Indo-Pacific. For instance, the amphipod regions for the world oceen and the Pecifc crustaceans Phronima colletti (Atlantic) and respectively. Their proposals apperently show a P.bucephale (Indo-Pacific), the Chaetognatha high degree of parallelism (Table I). Most oceanic Sagitta serratodentata (Atlantic) and plankton live in more than one region and/or S.pacifica (Indo-Pacific), and the copepod more than one ocean. In o survey of 952 species, crustaceans Pontellina plumata s.l. with Yan Soest ( 1979) found that 502 species ara Atlantic and Indo-Pacific forms. The western widely distributed between 50*N and 50*5. boundary of these Indo-Pacific taxa usually lies Beklemishev (1981) noted that 90 out of the 100 south of Port Elizabeth. The eastern boundary of species in his survey ere found in the same type of their Atlantic counterpart Is generally located regions in different oceens. south of Cape of Good Hope but occasionally extends Identification of oceanic zooplankton is general to the coastal water off southeastern Africa, ly based on morphological characters. When sometimes to Durban. The combination of the samples of o species from different parts of the African continent and the Agulhas Current system world oceen ara compared, trivial hut consistent seems to be an effective geographical barrier to morphological differences are sometimes noted In members of these pairs gf analogous species different geographical populations of so-called (Shih, 1986). -251- Table I Zoogeographies! regions of marine zooplankton according to Beklemishev (1971) and McGowan (1974). REGIONS ALL OCEANS PACIFIC CHARACTERISTICS (BEKLEMISHEV,1971) (MCGOWAN, 1974) Primary oceanic cyclic Subarctic & Subantarctic, Large-scale oceanic gyres, communities North & South Central, & recirculation present Equatorial provinces Secondary oceenic North & South Transitional Transitional zones between terminal communities provinces large-scale gyres;strong eest west currents present Secondary distant- Eastern Tropical Pacific Area between large-scale neritic terminal province oceanic gyres and continental communities coasts; medium-scale & stable eddies present Several pairs of intraoceanic analogous species outside their normal range of distribution because 8re found in McGowan's Eastern Tropical Pacific they are frequently carried awa/ by oceanic province. Each pair contains one species widely currents or other moving water bodies. Wiebe & distributed In the tropical and subtropical Boyd ( 1978) and Boyd et al. ( 1978) reported the Indo-Pacific and another limited to the eastern deterioration of populations of the western North Pacific, with an overlap in the latter region, e.g. Atlantic Slope Water euphausiid, Nematosceiis the Chaetognatha Sagitta pacifica (Indo- megalops, entrapped In Gulf Stream cold core Pacific) and S.bieri (E.Pacific), the copepod rings when the cold core waters of the aging rings crustaceans Pori teil ina plumata (Indo- gradually sssumed the biological and physical Pacific) and P.sobrina (E.Pecific), arid the characteristics of the surrounding Sargasso Sea. amphipod crustaceans Phronima stebbingi Tumantsava (1981) recorded the change of with Indo-Pacific and East Pacific forms. The planktonic community structure in the aging oceanography of the eastern tropical Pacific is upwelling water of the eastern Pacific. These complicated by a strong upwelllng system and the reports clearly demonstrate how a population of a convergence and divergence of several oceanic species end a community in an ecosystem may currents es well ss by the O2 minima (Wyrtki, react to a changing environment. Matsuda ( 1982) 1967). The coexistence of both members of examined changing environmental factors acting analogous species in this unstable oceanic upon known physiological processes In some environment does not conform with the general littoral and terrestrial animals, creating new belief that spéciation requires geographical regulatory genetic changes, and leading to species separation or other isolating mechanisms. evolution. In a "stable" environment, spéciation cannot take place if there is no isolating mechanism to PLANKTOPATRIC SPECIATION - A HYPOTHESIS prevent gene flow between different populations. In a changing environment such as an eddy, a cold Cceenic planktonic animals are sometimes found or warm core ring, a meander of a current, an -252- upwelling, or an area of convergence and The hypothesis of planktopatric spéciation may divergence, the biological and physical character explain the coexistence of both members of istics will change es the water travels from one several analogous species pairs in the eastern area to another. These changes consequently tropical Pacific where mixing of waters from modify the community structure and aiso alter the different origins Is most thorough and an isolating number and kinds of entrapped niches. If a mechanism is apparently lacking. population cannot adapt to the changing environ ment and find a niche, it will face elimination. If some individuals of a population can adept to the ACKNOWLEDGEMENT new environment and find a new niche, they will survive end probably proliferate. Some The author is grateful to Mrs. D. R. Laubitz for individuals or segments of a population possessing her constructive criticism. unusual alleles that were repressed in the original environment may develop in the new environment in a separate niche. As a consequence REFERENCES reproductively Isolated populations may become established. This type of species formation -BACKUS, R. H.. 6. R. FLIERL, D. R. KESTER, D. B. probably does not fit any particular mode of a SON 8. P. L. RICHARDSON, 1901. Gulf Stream spéciation described in the literature and is here cold-core rings: their physics, chemistry, and termed planktopatric spéciation which seems oily biology. Science, 2i2 : 1091-1099. . -BEKLEMISHEV, C. W.. 1971. Distribution of plankton to apply to oceanic plankton. es related to micropalaeontology. In: B. M. Funoell & W. R. Riedel (eds.). The Micropalaeontology of Oceans. Cambridge Univ. Press: 75-67. OONCLUD1NG REMARKS -BEKLEMISHEV. C. W.. 1981.Biological structure of Our knowledge of biogeography of oceanic the Pacific Ocean as compared with two other oceans. J. Plankton Pes., J : 531-549. zooplankton is mainly limited to the epipelagic -BOYD. C. M., P.H. WIEBE 4, J. L. COX. 1978. Limits species. The general patterns of distribution of of Nematoscelis megalops in Ute northwestern these animals ara highly correlated with those of Atlantic In relation to the Gulf Stream cold core rings. the major water masses end current systems II. Physiological and biochemical effects of ex (Beklemishev, 1971; McGowan, 1971). While patriation. J. mar. Ros., 36\ 143-159. water messes are the major biogeographic units -JOYCE. T. M., S. L. PATTERSON 8. R. C. MILLARD in the ocean, the mixing of water between JR., 1981. Anatomy of a cyclonic ring In the Drake different water masses is a recurrent event. In Passage. Daap-Sea Rea.. 28\ 1265-1287. areas where the mixing is pronounced, e.g. rings -MATSUDA, R., 1982. The evolutionary process In and eddies formed in tl» western boundary telitrid amphlpods and salamanders in changing currents (Backus et al., 1981 ) and the centre of environments, with a discussion of 'genetic assimilation' and some other evolutionary concepts. convergence and divergence In the eastern tropical Can. J. Zoo!., 60: 733-749. Pacific (Wyrtki, 1967), individuals of a popul -MCCARTNEY, M. S., L. V. WORTHINGTON 8. W. J. ation or a community are frequently entrapped in SCHMITZ JR.. 1978. Large cyclonic rings from the the migrating water and subjected to the change of northeast Sargasso Seas. J. Geoph. Rea., 83 : their immediate environment. These moving 901-914. hydrographic structures are therefore evolution -MCGOWAN, J. A., 1971. Oceanic biogeogr*>hy of tha ary laboratories of nature. With the high Pacific. In: B. M. Funnell & W. R. Riedel (ads). Tha frequency of mixing in some parts of the oceens Micropalaeontology oT Oceans. Cambridge Univ. and with the possibility (probably very Press : 3-74. insignificant) of the expression of new gene -MC60WAN, J. A., 1974. The nature of oceanic complexes of a population in a different environ ecosystems. In: C. B. Miller (ed.). Tha Biology ot ment, planktopatric spéciation may take place. tha Oceanic Pacific. Oregon State Univ. Press, -253- Corvallls : 9-28. -SHIH, C.-T., 1979. East-west diversity. In: S. van WHAT IS UNIQUE ABOUT OPEN-OCEAN BIOGEOGRAPHY; ZOOPLANKTON ? SIEBRECHT VAN DER SPOEL Institute for Taxonomic Zoology, University of Amsterdam, The Netherlands INTRODUCTION is found in the limnic environment, in soil and in the tropical rainforest. In the open ocean the Specietion and distribution are frequently three-dimensionality is only more marked then considered to differ in the pelagic environment elsewhere. when compered to the terrestrial one. These Zooplankton lives in seawater, a constantly differences are explained by the absence of mixed and extremely large substrate without barriers, the three dimensionality of the oceens, abrupt changes in conditions like found in the effect of currents making dispersal a long terrestrial environments. A normally vertically term phenomenon and the floating behaviour of migrating zooplankton species will in the area organisms. In this paper special attention is given that it comes from, meet no greeter changes in to the last phenomenon. most conditions than if it were to migrate In 1887 Victor Hensen defined (zoo)plankton as horizontally across ali oceens. If this special (animals) passively drifted about by water move character of the environment induce the unique ments (Hensen, 1887). Does this passive drifting ness of open-ocean zooplankton distribution, then determine dispersal and distribution. Is the it has the same consequences for nekton, for unique character of zooplankton related to its phytoplankton, and probably to a lesser degree, behaviour in space and time? If we have to answer aiso for benthos. But does not the present this question negatively the biogeography of conference combine plankton end nekton precisely plankton is no longer unique, but probably the because they both show the same typical definition of plankton is incorrect. phenomena? Many examples are known of different species showing, in one current system, different patterns; sometimes, for example, two allopatrlc TWO POSTULATES (geographically, horizontal os well as vertical, separated) species are sympatric with a third With regard to the large area available we should species although all three are dependent on the realise that distribution is not only the result of same current system (Yan der Spoel & Heyman, the environment, of the seawater and its basins, 1983). This seems to contradict the hypothesis but aiso of the expression of life; thus that passive floating directly determines distrib distribution develops by interaction between the ution. Some species are known to be transported influences of the environment and the behavioural by one and not by another current, therefore and physiological expression of life as it is fixed passive drifting does not, on its own, determine in genetic structures. Within the range of a taxon dispersal. "Passively drifted about" certainly there is harmony between animal and environ contributes to dispersal of specimens but seems ment; outside it there is conflict. "Arguments" not to contribute to dispersal of populations and maintaining this conflict mey be raised by the distribution, consequently not to a unique environment, by the organism or, as is usually biogeography. the case, by both at the same time. The three-dimensionality of the environment of As a first hypothesis it is here postulated that marine plankton is typical but essentially not "in plankton it is not the influences of the unique as it is aiso the environment of nekton and environment but the characters of the organism -255- that chiefly determine the range of a species expressing themselves as fronts or barriers, This makes the biogeogrephy of plankton and which by fluctuating keep ranges smaller than nekton unique. Translated into biological terms it possible ara not expected to be limiting either. means that population dynamics restrict the One strongly fluctuating condition is the available dispersal and distribution of species to a nutrient concentration at higher latitudes, in relatively small erea, smaller than the niche seasonally mixed waters and in near-shore 8reas. which is available if a.o. drifting were to controle However, this fluctuating condition directly distribution (cf. Angel, this volume; Katona, this influences the populations and not the geographic volume). Mayr (1967: 201, 468) summarized size of the ranges. the adaptations of taxa which enables them to A breakdown of the gene pool when the range utilize more of the available niches, and as a becomes very large, when the entire available consequence accepts the incomplete occupation of a space is occupied, can in general be rejected as an niche when population dynamics ara not fully explanation of restricted ronges as there are many adapted. species, oceanic 8S well 8S terrestrial, with very The biogeography should be studied with the large distributions which one still recognize as clear understanding that its is different from good species. ecological biogeography (Mayr, 1982). The A solution adopted here is to accept a second population density, the number of specimens per hypothesis: "Evolution in the pelagic environment unit of space, is not considered at this place, ( in large populations) is too slow to reach optimal rather, the geographic space occupied by the total adaptation to the conditions of the large area of populations of a taxon. Superimposed on the available, resulting in smaller ranges than fluctuation of the geographic size of populations possible". Or environmental changes ere still too are, of course, the usually sinusoid density and quick which is the same as evolution is too slow. population structure fluctuations (Voronina, Though the ranges ere smaller than the 1978). The above hypothesis can only be accepted available space, the individual populations may be if it is coupled with an explanation of why the extremely large. In these large populations, process of evolution did not succeed in developing changes of the gene pool are difficult to achieve. It species that can occupy the total area available to must be clear that a relatively small number of them. large populations in a range aiso depresses rates The total available area is considered to be the of evolution. Slow evolution implies not only low entire ocean, or that section of it without relative spéciation rate, inperfection of adaptation to sharp discontinuities in environmental factors. In specific conditions and great potential flexibility cases where population dynamics restricts the of the gene pool, but aiso little tendency for new occupied area it is e.g. reproduction, mortality, genetic adaptations resulting in new ranges. With maximum distance permitted between specimens the great flexibility of the gene pool, the within and individual movement behaviour which population flexibility is meant. It is visible in restrict distribution and which, therefore, did not many species es temporary ecological adaptations, adapt "optimally" during the process of evolution. polymorphism or polytypism. Or should we say adapt ' maximally"? Could it be profitable to be unable to occupy ali of the available area? A MODEL Adaptations are usually not maxima) when they ere optimal because "optimal" still entails In figure 1 a dynamic model of the major factors response to fluctuating environmental conditions determining population- and range-size Is given (Mayr, 1967). For plankton, is the size of the for three species 1, 11 and 111 considered to be in an available range aiso a fluctuating condition? This equilibrium state (RANGE IN EQ. STATE). The hardly seems to be the case, since the conditions effects of population dynamics, evolution and in the oceen and oceen size do not change strongly, environment are demonstrated here successively. not even in terms of geological time. Conditions, In figure I as well as 4 the ranges are pictured es -250- the range (D), and maximum density of organisms for effective mating (E). More reproduction ( + ), less mortality(-), and larger maximum distances allowed for effective mating ( + ) will result in population increase. However, in plankton the result is aiso range enlargement ( + ): the specimens move at random so that abundance (-concentration) drops in favour of range enlargement (-dilution). In plankton, drifting is usually very strong ( + ); specimens find each other as a rule by accident, so that nevertheless small distances are required (-) between Individuals. This has the effect that populations and ranges of populations tend to stay relatively small (-). Species interaction In plankton, indicated in figure 1, is never reported es an important phenomenon (cf. McGowan & Fig. 1 Dynamic model of plankton ranges of three Walker, 1985), perhaps not only by the fact that species: i, with the influences of population it is difficult to document. fluctuations; II, with niche size fluctations; and Evolution changes the species so that it may live III, showing the influences of population elsewhere in space or time; this can aiso be dynamics, evolution and environment. The expressed 83 'evolution alters the niche for a populations are grouped to show the influence of given line of descent. population dynamics as horizontal, and those of The effects of evolution on plankton are evolution and the environment as vertical shifts indicated with species II. When the range stays in the space available between barriers. A= local smaller than the area available, evolution is stop adaptations, B= new radiating adaptations, C= ped or slowed down, so spéciation (S) is at a low climate influences, D= expatriation, E= max. level (-), adaptation to specific local conditions effective density, EN» environmental influences, (A) is small (-), genetic flexibility stays high so EQ= equilibrium, 0» geomorphological effects, that the available niche (arrow on top of species M= mortality, R= reproduction, S= spéciation, X= II) stays or becomes larger (4). New genetic population dynamics, Y* evolution effects, Z» adaptations, e.g. in peripheral populations or environmental effects, += Increase, stimulation, founder populations are not developed ( - ) so that -= decrease, limiting, ------► = vector of no new ranges, indicated by the lower arrow ( - ) influence, or dispersal. are populated. Effects of selective pressure in plankton are slowly realized as the population size is very transformable quadrangles which may shift up and large in general ( "A" stays small). In populations downwards in the available environment that with high abundance genetic drift tends to create a becomes smaller at the underside and wider at the large percentage of homozygotes, thus tending to upper side of the model depicting in that way the reduce radiation and diversity. However, even in effects of environmental factors. The vertical these large plankton populations this reducing shift Is depicted as determined by effects of effect is not realised, and probably only the evolution and the size changes due to population formae of species ( Yan der Spoel,1971) can be dynamics are depicted as broadening and narrow explained by this effect, though the genetic drift ing of the quadrangles. must be largB (as "D“ Is large). For species I in figure 1 the major factors of In plankton, moreover, the environment population dynamics are pictured as reproduction (depicted at the right Sida in Fig. 1) is (R), mortality (M), drifting of specimens out of characterised by large, not sharply delimited -257- climartic belts (C)( + ) and gradual transitions in CONCLUSION environmental conditions (ENKO which render larger ( + ) available arcas. Geomorphology (G) As a conclusion one can state that zooplankton does not present open ocean plankton with many distribution (Fig. 3) is influenced not mainly by barriers (-) so that the niches are in general the environment, but by population dynamics vary large ( ♦ ). which keeps ranges small. A lack of evolutionary In my view everything combines to make the specialisation towards narrow and specific available area larger and the population smaller, environmental conditions makes the available so that the second floats 'uncontrolled' in the first. rangs larga. Therefore, it is almost logical to Comparing this with the dynamic model for e g. accept that: population dynamics and evolution terrestrial animals (Fig. 4), drawn along the same lines es that for plankton, great differences are obvious, even when only the factors are considered which were applied for plankton. Reproduction and mortality in terrestrial animals determine to a greater extent the range size than transport of specimens does, while species inter action by competition ( + ) frequently restricts the population (-). Ali other factors are, however, in favour of population enlargement ( + ). Evolution has gone much faster than In the see and spéciation (S) and adaptation (A) are both relatively frequent ( + ) which restricts niche size but not niche numbers while new adaptations (B) may enlarge the area into which a taxon splits off new populations. The geomorphology of the Fig.3 A plankton population partly restricted by terrestrial environment, in particular induces environmental vectors and largely by population small niche size, while climate and other dynamics and evolution (for explanation see environmental factors do not particularly enlarge Fig. 1 ). it. keep the size of the actual range in a sort of equilibrium. In terrestrial animals (Fig. 4) just the reverse is found. The environment keeps the populations In a given space and spéciation and adaptation, thus evolution, restrict the arae available, population dynamics alone may work Io enlarge the range. Newly evolved adaptations may stimulate thi3 too. Here environment and evolution keep the range in a kind of equilibrium while population dynamics fluctuates to get maximal profit out of this equilibrium. Of course Intermediate situations between the Fig.2 A plankton population range, net restricted two ara possible. In plnnkton the environment by environmental vectors, but by population may have an influence (Fig. 5), but then, dynamics and evolution (for explanation see population dynamics aiso restrict the range. In Fig. I ). terrestrial animals boundaries are known which -258- Fig.5. A non-plankton range influenced by evolution and population dynamics but limited by environmental conditions (for explanation see Fig. 4 Dynamic model of non-plankton ranges of Fig. 1 ). three species; I, with the influences of population fluctuations; II, with niche size fluctations; and races or subspecies can develop when there is a III, showing the influences of population lack of separated populations. Aiso distribution dynamics, evolution and environment, in the same limits ara usually markedly different for species manner as In figure 1. occurring in the s^e area or province (Fig. 7). From figures 1 and 2 it is therefore clear that are not induced by the environment or by the uniqueness of zooplankton biogeography is species interaction (Fig. 6) but here primarily induced by: evolutionary effects, as distance barriers, 1. the effect on population dynamics, by drifting restrict the range and the population dynamics do about of specimens, thus not directly by the not do so directly. displacement of specimens or ranges, • Accepting the extreme hypotheses given above, "population dynamics restrict ranges", "evolution Is slower then on land" and "there is an equilibrium between population dynamics and evolution", spéciation above species level will hardly be possible and distribution borders of taxa will usually not be congruent as they are determined by the individual species and not by a general external factor. This is exactly what is found in nature, evolution In the sea is slow , only 40% of ali. taxa live in the soa that covers 70% of the eerth, so the rate in producing numbers of taxa is 4 times as slow as on land, and of the small number of taxa hardly any shows geographic spéciation above the subspecies level. Usually adaptations ara ecophenotypic, giving rise to varieties. It is logical that with decreasing Fig.6. A non-plankton range influenced and partly number and increasing size of populations the limited by evolution processes but not by evolution rate drops, no polytypy, no geographic population dynamics (for explanation see Fig. 1). -259- 80 70 N . 1, \ ■v / ■ S/ ’ B fC ■ : > 1. F1g.7. Ranges of North Atlantic Cold water taxa to show the non-congruency of ranges. A- Nitzschia cylindrica ; B- Clio pyramidata forma pyramidata ; C- Salpa fusiformis coldwater form;D= Calanus helgolandicus ;E= Sagitta tasmanica ; F= Limacina retroversa. 2. slow evolution and low spéciation rate ( in vary adaptations (eoophenotypes), are frequent, large populations which still do not fill the 3. the character of the sea. a large substrate available area) in spite of local and temporary without abrupt differences or changes. -260- As a final conclusion and working thesis, a new definition for zooplankton is proposed : "Zooplankton comprises species whose speci mens are passively drifted about by water movements within the stable range (defined by population dynamics) occupied by the (large, temporary or permanent) populations" This definition makes it possible to apply normal biogeographical principles to planktonic taxa es the populations are stable units again ( M euchila, this volume). However, when a taxon by its own genetic characters can restrict its distribution in space, it can for the sama reeson restrict its distribution in time This means that extinction is determined by the taxon itself, by its genetics, and explanations of extinction through catastrophes become unnecessary. ACKNOWLEDGEMENTS The anonymous reviewers are cordially acknow ledged for the fine work they did. REFERENCES -HENSEN, V., 1887. (Jeta1 die Bestimmung des Planktons. Komma wiss. Un ters. dt. Meara Kiai, XII-XVI : 1-107. -MAYR, E.. 1967. Artbegriff urd evolution. Varl.P. Paray, Hamburg, Barlin: 1-617. -MAYR, E., 1982 The growth of biological thought. Belknap Prtss Harvard Untv. Cambridge, Lood. : 1-974. -MCGOWAN, J. A. L P. W. WALKER, 198S. Dominance and diversity maintenance in an oceanic ecosystem. Eco/. Monogr., 55(1): 103-118. -VAN DER SPOEL, S.. 1971. Some problems in infraspecific classification of holoplanktonic animals. Z. zoo!. Syst. Evo/.forsch., 9(2): 107-138. -VAN DER SPOEL, S. & R. P. HEYMAN, 1963. A comparative altas of zooplankton. Biological patterns in the oceans. Bunge scient. Puhi., Utrecht: 1-186. -VORONINA. N. M„ 1978. Variability of ecosystems. In: H. Charno* & 6. E. R. Deacon (eds) Advances in Oceanography. Plenum Press New York &. London: 221-243 -261- PATCHINESS AND THE PARADOX OF THE PLANKTON E.L.VENRICK Scripps Institution of Oceanography, U.S.A. INTRODUCTION theories of niche diversification and dis equilibrium/disturbance. Although the predation Biogeography Is the study of species ranges, hyphotheses are appealing, they have not yet been concordance of species ranges and the factors formulated in a way that can be tested in the field which influence these ranges. One approach is to and can not be considered further here. consider the species whose ranges overlap in some Niche diversification theories predict that environment and investigate the mechanisms species abundance centers should be separated which facilitate their coexistence and which according to some predictable spatial or temporal regulate their relative abundances. The major structure in the environment. We have detected pelagic habitats support far more species than neither horizontal gradients nor seasonal cycles expected from the general ecological principle within the Central Pacific (Hayward et al., that competing species in an equilibrium system 1983). The primary environmental structure can not coexist indefinitely. Three types of available is provided by the vertical gradients of hypotheses have been developed to explain the light, primary productivity, nutrients, apparent coexistence of apparent competitors in temperature, etc. McGowan investigated the apparently equilibrium ecosystems. Niche spatial distributions of 123 species of copepods diversification hypotheses (Schoener, 1974) collected in 62 bongo net sample» from six to predict that similar species can co-occur because eight depth ranges during a ten dery period in they have specialized to make use of diffent parts August-September, 1968 (McGowan & Walker, of the spatial or temporal habitat, thus reducing 1979). Only seven patterns of vertical competitive interactions. Disequilibrium or distribution were detected. The vertical patterns disturbance theories predict that competitors were stable horizontally, and wero present in co-occur because the ecosystem is not at every survey between 1964 and 1969, equilibrium, but instead environmental regardless of season (Fig. 1). fluctuations occur on such a scale es to prevent The vertical distributions of more than 200 the ultimate exclusion of competing species phytoplankton species were determined from (Hutchinson, 1961; Rlcherson, et al., 1970; seventy two samples collected by water bottles Paine & Levin, 1981). Predation theories from eighteen depths at each of four stations (Darwin, 1859; Caswell, 1978) predict that during June, 1977 and August, 1978 (Venrick, predation pressure either maintains the 1982). Only two associations of species could be abundances of the prey species below the level of defined, one above 100- 120m, the other below resource limitation, or occurs in a heterogeneous 75-90m. These appear to correspond to the manner, thereby keeping the ecosystem in estate nutrient-limited and light-limited regimes of disequilibrium. defined by t'ppley et al. ( 1973). The chlorophyll maximum layer corresponds most closely to the region of transition between the two associations. DISCUSSION These two associations are consistently present and were essentially unaltered by a major We now have nearly twenty years of biological and enrichment evani that was observed in August, environmental data from the diverse arid stable 1980 (Fig. 2). With neither zooplankton nor ecosystem in the North Pacific Central gyre. We phytoplankton is there evidence that niche have used these data to test the predictions of the diversification hss occurred among the species to depths, Fig. were memters eo- the of diversification observed. over vary true, environment to fluctuations species plankton Levin, reefs postulated predict hypotheses long "behaviour". 175 1961; DEPTH (m) Tins test 600 occa extent 1 behavioral lasting copepod a from combined Mean J and 16 1981). the these Richerson on that, ranee should I of disequilibrium/disturbance which year (24spp) small four Intertidal for neccessary percent disturbances One is which in species at failure portioning. hypotheses of ( the McGowan better among these period some cruises. McGowan seals, have become the might diversification el pelagic of are collected al., scale the communities environmental zooplankton large including Illustrated of a short to vertical II has To of Groups using & very (I3spp) number ecosystem 1970) postulate explain abundant. niche in tropica! the Walker, used numbers term coherence space during extent abundance limited three mhjrators, wore several to of by disequilibrium diversification takes the rather (eg. or forests, copepod the (Hutchinson, 1979; ID nine that fluctuations The the that expedition* defined of time, persistent (llspp) the rao/j massive, (Average analyses Paine theories species o cruises • o o phyto data this — — scales coral Fig. niche form only species rare than * o o o on of is of & 17). % CLIMAX URSA CLIMAX ZETES -262- night the of EZ per MAJOR Climax basis (8 a I collected collected were disequilibrium observation abundances data association, more, tendency were congener (Venrick, assumption against likely /disturbance which (Fig. more Pacific. 1978 spp) recurrent The Phytoplankton Jon Sept Aug Sept I of were group 3). they were tested predictions to among than the traversed 1969 1968 1966 1964 V On was be during during the (5spp) used. members eo- distributed group no 1982). 1968 competitors, restricted to 100 that is there by in in the occurred scale be theories. NIGHT predictions For consistent the two present data the date. congeneric rare major comparing present) congeneric of positively 1977 of There other opposite W83 separate the enriched to space have independently. For species 5ZI less congeneric the portions (coherence) disturbance and groups (5spp) a was groups with or data aiso often direction. correlated. pairs of tendency the species studies. time no period become 1978 from ali been predictions disequilibrium of phytoplankton V SU than evidence in species did times and the et Indeed, hypothesis (4 with the Under are any of Further 1 examined abundant for spp) expected different 977 Neither VII, Central upper I960 of of pairs NIGHT most that that 8nd the the day the the the of -263- Jvî.E 1977 AUGUST 1980 types of organisms, collected by different ABjNCASCE lee' »/lOOmi) techniques and on different scales, and analyzed independently produce the same results. For neither group of organisms do we find convincing evidence that processes of niche diversification or of disequilibrium/disturbance are responsible for the maintenance of species diversity in the North Pacific Ocean. CONCLUSION Taken as a whole, our results underscore the gap between the concepts of classical ecology and the reality of the pelagic ecosystem. The problem is two-fold. The first is historical. Modern ecology has its roots in the natural history observations of the past. Of necessity, these were observations of accessible and visible ecosystems. The tenents of modern ecology havo been formulated for ecosystems with physical structure: structure in the sense of trees and rocks and rabbit holes; structure that can be hidden in and nested upon and eaten. Few theoreticians have focussed their attention ori the relatively unstructured, pelagic communities. At the same time, the traditional tools available to test the theoretical predictions are not Fig. 2 Yertical distributions of species In the first available to pelagic biologists. We can not observe two recurrent groups of phytoplankton species the system directly; we can not observe species defined froirulata collected in !977ond 1978. A. ambits and interactions, but must infer them. We Mean abundances in 1977 (n=3). B. Mean can not manipulate the system, translocate abundances in 1980 (n=2). individuals, remove individuals, or exclude individuals from a portion of the system. Thus, (Yenrick, in prep.). A total of 301,339 cell3/m2 pelagic biology does not produce the sorts of were enumerated In 1980. This compares with ecological observations that have traditionally 214,520 cells/m2 in 1977 and 195,981 tested and directed theoretical formulations. cells/m2 in 1978, a mean increase of 4758. There If we are to procédé toward understanding the was no detectable change in the rank order of regulation of community structure in the pelagic species abundances. Nor was there any evidence ecosystem, this gap between theoretical 8nd that tile rarer species increased more frequently pelagic ecology must be closed. We need to know than the abundant ones. Except for the increase in the specific predictions of community regulation biomass, the phytoplankton associations were models for the pelagic ecosystem. We need to virtually unchanged. Among neither zooplankton know, for instance, on which scales of space and nor phytoplankton is there evidence that rsre time disturbances are likely to be effective in species ever become abundant as predicted by preventing competitive exclusion, how large the disequilibrium/disturbance theories. resultant abundance fluctuations will be, and how The strength of our results lies in their many species can indefinitely co-occur under the consistency. Observations on two very different disequilibrium/disturbance models. We need to ; 800 U 600 3 400 uj 200 >0 80 100 I 160 H30 RANK OF SPECIES Fig. 3 Abundonces of copepod species. Dota points are the means of seven cruises : Jan. 1966, Sept. 1964; Sept. 1968; Aug. 1969; Oct. 1971 ; June, 1972; Fib. 1973. Grey bars indicate the range of abundances (McGowan*Walker, 1985; F1g.3.). know the specific characteristics of predators REFERENCES which lead to predation enhanced prey diversity. For our pert, we must attract the attention of -OARWIN, C. R.. 1964 (1859). On the origin of theoretical ecologists by providing data from species. Reprint edition. Harvard Univ. Press. pelagic ecosystems which are suitable for testing Cambridge, Massachusetts: 502pp. the predictions of their models, thus presenting -EPPLEY, Ft. W.. E. H. REN6ER, E. L. VENRICK & il. M. clear documentation of the apparent fellings of MULLIN, 1973. A study of plankton dynamics and their theories in pelagic systems. nutrient cycling In the Central Gyre of the North Pacific Ocean, iimnoi. Oceanogr., f8 : 534-551. -HAYWAPD, T. L. E. L VENRICK * J. A. MCGOWAN. ACKNOWLEDGEMENTS 1983. Environmental heterogeneity anJ pleurion community structure In the Central North Pacific. J. This work WB3 supported by the Office of Naval mar. Ros.. 4i: 711-729. Research and by the Marine Life Research Group -HUTCHINSON, 6. E., 1961. The paradox of the of Scrlpps Institution of Oceanography. I am plankton. Am. Mai., 95 : 137-144. -MCGOWAN, J. A. & P. W. WALKER, 1979. Structure indebted to John McGowan, without whom none of in the copepod community of the North Pacific Central this work would have been eccomplished, and to 6yre. Leoi. tlonogr., 49: 195-226. two perceptive reviewers who recognized thai the -MC60WAN, J. A. & P. W. WALKER, 1985. Dominance primary purpose of this paper is to provoke and diversity maintenance in an oceanic ecosystem. thought, discussion and argument. I apologize for £coi. tlonogr., 55: 103-118. Ignoring the intriguing 1981 model of D.Tilman -PAINI;, R. T. & S. A. LEVIN. 1901. Intertidal (Am.Nat. 116: 362-393); this was due more to landscapes: disturbance and the dynamics of pattern. lack of space thaii lack of Interest. EcoUionogr., 5/ : 145-178. -263- -RICHERSON, P.. R. ARMSTRONG & C. R. 60LDMAN. 1970. Contemporaneous disequilibrium, a new hypothesis Io explain the ’paradox of the plankton'. Proceed. Nairi. Acad. Sei., 67'. 1710-1714. -SCHOENER, T. V/., 1974. Resource partitioning in ecologist communities. Science, 105: 27-39. -VENRICK. E. I... 1982. Phytoplankton in an oligo tropha ocean: observation and questions. Eco/, tlonogr., 52: 129-154. -266- TRANSITION ZONES AND SALP SPECIATION JAAP DE VISSER Foundation for the Advancement of Oceanographic Research, the Netherlands INTRODUCTION in one or more points in the cline there is a sudden drop in the number of muscle fibef's (the Salpidae (Tunicata, Thaliacea) are widespread step). When we are dealing with a stepped cline over ali the ocean. Some species are almost investigation of the transition zones or boundaries cosmopolitan, for instance Salpa fusiformis, might give indications for phenetlc end/or genetic S. maxima, Iasis zonaria and Thalia differences between the demes living on both sides democratica. Some species which are less of the step in the cline. eurythermous do not occur in the Mediterranean Material collected by the Amsterdam Mid North ( Traustedtia multitentaculata, Weelia Atlantic Plankton Expeditions (1980-1983) cylindrica ). There are species whose distrib proved to be very suited to show the nature of ution area is confined to the tropics of the Indian these dines in more detail. Stations were made at and Pacific Oceans ( Helicosalpa younti, relatively short distances and along a North-South Ritteriella picteti). transect at approximately 30* West in the North At last there are species with a very restricted Atlantic, ranging from 55'N to 25*N (Fig. I). di3ti ibution area, for instance Salpa thompsoni Samples were taken at discrete depths: 0-50m, having a circumpolar distribution in the antarctic 50-loom, I00-200m, 200-300rn, 300 andsubantarctlcand Salpa gerlachei occurring 400m, 400-500m, 500-1000m end occeslonely only on the western edges of Antarctica (cf. Van down to 2000m, in the four seasons of the year. Soest, 1975a: Table IV). Subarctic water, Polar front, North Atlantic In some cosmopolitan species (cf Van Soest, Drift, Temperate water, Subtropical water, 1975a: Table III) the number of muscle fibers Is Sargasso Sea water, Canary current and below variable. For example, Salpa fusiformis depths of 800m deep Meditereneen outflow, shows a high number of muscle fibers in the Arctic and Antarctic intermediate water were temperate wetermasses and a low number in the tropical/subtropical parts of the oceans in both the Atlantic and the Indo-Paciflc. This demonstrates biantitropical clinal variation going from high numbers of muscle fibers at high latitudes towards low numbers of muscle fibers at AMNAPE1980—19&3 low latitudes. CLINES AND SPECIATION. These biantitropical patterns might be smooth dines, a gradual decrease in the number of muscle fibers going from high latitudes towards low latitudes, or stepped dines (sensu Huxley 1939): •) AMNAPE proj. IOTA rap. no. 24 supported by a Fig. 1 The transect of the Amsterdam Mid-North grant of the Netherlands Ministry of Education and Atlantic Expeditions. Sciences. -267- S8mpled( see Yan der Spoel 1981,1985 ; Yan der fiber counts, high population density in spring Spoel & Meerding 1983). and a small ratio of oozoids/blastozoids, showing Salpa fusiformis has been investigated no clear diurna] vertical migration; a southern closely for the spring 1980 samples. It shows a one with a low number of muscle fibers, low stepped dino with a high number of muscle fibers population density and a high ratio of north of 38‘N and a low number of muscle fibers oozoids/blastozoids, performing diurnal vertical south of 38*N, these low numbers being the seme migration. In between there Is a low abundance as numbers previously reported by van Soest but a restricted geneflow is In existence as their (1972) for the tropical Atlantic. In between, at is evidence of interbreeding at 38‘N. Material 38‘N at the step in the cline, intermediate from other seasons is In preparation and does not numbers of muscle fibers are found (Fig. 2). conflict with the description of the populations mentioned above. Muscle fiber variability in salps seems to be linked with the genotype of definite populations (cf. van Soest, 1975 b). These populations can, if genetic differences accumulate, become separate species, as might have fairly recently happened in the closely related S. thompsoni and S. gerlachei . I I I I I I il Allopatric spéciation Is not likely to have happened because complete isolation of populations in for example a tropical or Carribeen warm water and a Mediterranean cold Fig. 2 Number of muscle fibers in Salpa water population during, for instance, the fusiformis in the Mid-North Atlantic Ocean. Weichselien glacial i3 hard to imagine. In the southern hemisphere these processes are even Population density and vertical migration show more difficult to envisage. a variation related to the morphological variation. True sympatric spéciation is aiso ruled out North of 38*N no clear diurnal vertical migration is found (Figs 3a & 3b). South of 38‘N Salpa fusiformis does perform diurnal vertical migration. In night samples It is only found In the upper water layers (0-300m) while during the day it Is restricted to the more profound water layers (300-1000m). 800 - \) North of 38‘N densities ere very high, south of 1000-I this latitude they ere low. In between, in the ares depth (m) around 35*N the abundance is extremely low (De Visser & Yan Soest, in the press). There are aiso differences in the reproduction of both demes. North of 38‘N the ratio oozoids/blastozoids is 1/10 up to 1/100. This points towards rapid growth of the (feme by 800 - asexual reproduction and is reflected in the high 1000 -i density. South of 38‘N the ratio oozoids/ blastozoids is 10/1 and in part of the samples blastozoids are not even found. The picture that emerges is that of two Fig. 3 Vertical distribution of Salpa fusiformis populations: a northern one with high muscle in the Mid-North Atlantic, a, deytime; b, night. -268- because adaptation to different ecological OONCLUDINO REMARKS circumstances clearly exists along a North-South gradient. The small transition zone between the in salps this spéciation perhaps should be called populations of S. fusiform is points towards Sisyphean spéciation. Because of their sexual/ dinoi parapatric spéciation, a spéciation of two asexual breeding cycle salps ara able to multiply populations while maintaining geneflow. If the very fast (cf. Heron, 1972). Variation in step in the cline becomes steeper an adaptive population densities on one or both sides of the discontinuity may be reached which would result step in the dine depending on, far instance, in two separate species (cf. Endler, 1977; White, seasonal Influences may result in a steeper step 1978; Bush, 1981). one season and a smoother step in another season, The step in the dino, associated with low thus resulting in a never ending process of population density enables the populations to build spéciation, as long as environmental conditions do up genetical adaptations strong enough to not change drastically. If conditions do changa, distinguish them from each other. resulting in a reduced geneflow for a longer Some kind of stasipatrlc spéciation, possibly not period, then, due to clinal variation, spéciation visible because of dina! parapatric spéciation, will occur in a relative short period compared to can aiso be Involved. This presumes a chromo more homogenous species. somal reerrangment favorable to selection mechanisms if homozygote but reducing fecundity when It appears In the heterozygote specimens. REFERENCES The difference with the dinoi model of spéciation Is that the stasipatrlc one presumes a change in -BUSH, G. L, 1961. Stasipatrlc Spiridion tnd rapid the karyotype which reduces fecundity in the evolution in animals. In: W. R. Alchley & D. S. heterozygote although the dimunition need not at Woodruff (ids): Evolution and Spéciation. Essays ali be complete. The clinal parapatric model of in the honor ofil. J. D. White. Cambridge Unlv. Press, Cambridge: 201-218. spéciation presumes changes in genes (point -ENDLER, J. A., 1977. Geographic variation, mutations) which need not reduce fecundity in the spociaiion and dinos. Princeton Univ. Press, heterozygotes. To see wether or not thero ara any New Jersey: 246pp. chromosomal differences involved between the -HERON, A. C., 1972. Population ecology of a populations it is neccessary to study the karyo colonizing species: the pelagic tunicate Thalia types of these organisms The low population democratica. I. Individual growth rota and re density in the vicinity of the step in the cline generation time. Ooko/ogia, IO (4): 269-293. might point towards a reduced fecundity of -HUXLEY. J. S., 1939. Clines, an auxiliary method In heterozygotes. taxonomy. Bijdr. Diark., 27: A91-520. Whether or not spéciation related to the dines -VAN SOEST, R.W.M., 1972. Latitudinal variation In in muscle fiber variation of salps occurs depends Atlantic Salpa fusiformis Cuvier. 1804 (Tunicata, on the capacities of reducing the fecundity of Thaliacea). Beaufortia, 20 (262): 39-68. heterozygotes by the chromosomal rearrangments - VAN SOEST, R. W. M., 1975a. Zoogeography and spéciation In the Salpidae (Tunicata, Thaliacea). in the stasipatrlc model of spéciation and on the Beaufortia, 23 (307): 181-215. population strudure of the species in the clinal - VAN SOEST, R. W. M., 1975b. Thaliacea of the parapatric model. If population densities on both Bermuda area. Bull. coot. dus. l/ntv. sides of the “step" in the cline become high enough Amsterdam J(2): 7-12. to enlarge geneflow between the populations, the - VAN DER SPOEL, S.. 1981. List of discrete depth cline might become more smooth. samples and open net hauls of the Amsterdam Mid North Atlantic Plankton Expedition 1980. Bull. root, dus. Univ. Amsterdam, tf(1): 1-10. - VAN DER SPOEL, S.. 1985. List of discrete depth samples and open net hauls of the Amsterdam Mid North Atlantic Plankton Expeditions 1982 and 1983 -269- (Project 101 A). Bull. zool. Mus. Univ. Amsterdam. IO (17) : 129-152. - VANDER SPOEL, S. & A. G. H. A. MEERDING, 1903. List of discrete depth samples end open net hauls of the Amsterdam Mid North Atlantic Plankton Expedition 1981. Bull. zoo!. Mus. Univ. Amsterdam, 9 (9): 77-91. -VISSER. J. DE & R. W. M. VAN SOEST, (in the press). Salpa fusiformis populations of the North Atlantic. Biol. Oceanogr. -WHITE. M. J. D., 1978. Modes of Spéciation. Freeman and eo., San Francisco: i-viii, 1-455. -270- FACTORS AFFECTING THE BIOGEOGRAPHY OF MID TO LOW LATITUDE EUTHECOSOMATOUS PTEROPODS JOHN H. WORMUTH Department of Oceanography, Texae A&M University, U S A INTRODUCTION collected The mesh size ( 0.333mm) was constant for ali tows. Deep tows extended well below the Two of the questions asked by biogeographers are: vertical range of ali common species. In addition "What are the main patterns of species to these samples, ali available pertinent distribution and abundance?" and "What maintains literature wss examined to supplement findings the shape of these patterns?" ( McGowan, 1971). (Table II). To answer these questions we usually U9e For this group of zooplankton, the factor which geographical distributions which represent a most often makes quantitative comparison to other composite of data from many years and different studies impossible is differences in mesh size. sampling schemes. The quantitative interpretation of these distributions can be difficult due to many sources of variation including both natural and sampling variation. In addition, oblique net tows are most often used because many more of them exist in collections than depth-specific samples so they yield wider geographical coverage. The broad features of geographical distributions can certainly be discerned in this way, but the quantitative aspects (i.e. where are the regions of high and low abundance) are most likely to be obscured These quantitative aspects, however, are most likely to give us insight beyond simple correlations into those features of the environment which have a causative effect. MATERIALS ANO METHODS This paper examines data on euthecosomatous pteropoda collected with a 1m2 MOCNESS (Wiebe et al., 1976) over depth intervals of 100 or 150m to depths of 850m or 1000m and over intervals of 10-25m to depths of 200m. Samples were collected in different environments: the Slope Water Region off the East Coast of the United States, Oulf Stream Cold-Core Rings, Gulf Stream Warm Oore Rings, e Gulf Stream itself, the Sargasso Sea and both warm and cold core "rings" in the northwestern Gulf of Mexico (Fig. 1, Table I). In ali cases in situ temperature and in most Fig. I The sampling aress in the northwest Guii of cases salinity wera monitored as samples were Mexico and in the northwest Atlantic Ocean. -271- Table I Number of MOCNESS tows (8 samples per tow) by environment used in the data base. Environments 0 to < 300m 0 to >700m Day Night Day Night Slope Water Region 2 2 7 6 Oulf Stream Cold-Core Ring Centers 1 3 IO 9 Oulf Stream Cold-Core Ring Fringes - - 2 5 Oulf Stream Warm Core Rings -- 2 2 Sargasso Sea 2 3 8 9 Oulf Stream - - 1 - Oulf of Mexico Cyclonic "Rings" 8 12 1 - Oulf of Mexico Antfcyclonic Rings 7 8 1 - Totals 20 28 32 31 Work done by Snider (1975) in the Quit of Mexico showed tremendous differences between the size frequency distributions of Limacina inflata and L. trochiformis collected in the two sides of a bongo net when different mesh sizes were used (0.183 and 0.505mm) (Figs 2, 3). Other investigators have found similar differ ences, but this was the first time the samples were collected simultaneously. Although many zooplankton samples used in biogecgraphic studies probably have been collected for general reference and may, therefore, have depended on available equipment, this quantitative incom patibility underscores the need for some kind of standardization of sampling equipment and techniques in order to derive maximum information from these expensive samples. 04 .1» 200 260 5 2 564 4« 468 520 572 624 676 .721 .780 852 Sample sizes of about 1000m3 of water sampled IUXiUuU CPMtfcVON (*«> appear to be adequate to collect most species and to Fig. 2 Size distribution of Limacina inflata give reasonably consistent abundance estimates. taken simultaneously with "Bongo" nets of 0.183mm and 0.505mm mesh (O-100m, night) (from Snider, 1975). -272- Table II Summery of previous distributional pteropod research. Oeographte Depths Type Mesh Discrete Depth Investigators Area Sampled of Net Size (mm) Horizons (m) Sampled? North Pacific O-MO 1 meter .650 some McOowon.1960 Western North variable 70cm Disc graded some Moore, Owre, Atlantic overy net «Jones & Dow, 1953 Bermuda variable 70cm Disc graded yes Wormei 1, 1962 overy net Western North surface 0.5 meter .200 no Chen & Bé. 1964 Atlantic Northwestern 0-150 1 meter .505 yes Myers, 1967 Sargasso Soa Western North surface 1 meter .505 no Vecchione, 1979 Oulf of Mexico 0-100 70cm .333 yes Snider. 1975 —------m Dongo Caribbean 0-4000 75cm Disc graded yes Hangen son. 1976 overy net Western South 0-137 60cm .333 no Dadon, 1984 Atlantic “bongo' Indian Ocean 0-200 IOS net .333 no Sakthivel.1975; 1977 South China 0-200mwo 1 meter .640 no Rottman, 1978 Soa RESULTS undergoes fairly rapid increases in water column abundance which correlate with an increase in Of ali species identified, the mo3t abundant and food supply (Wormuth, 1985). In tht> absence of interesting species in most environments wœ measured growth rates, one way to demonstrate L.fnf/ota. This species is a warm water the increase Is to examine size frequency cosmopolite in the Pacific with highest abundance distributions both inside and outside of the rings In areas of mixing (McGowan, 1971 see sampled. When this was done the corresponding Fig. 1.22). Two different Gulf Stream Cold-Core Sargasso Sea populations outside of the Gulf Rings were sampled twice each during their life Stream Cold-Core Rings had significantly smaller histories. The results show that L. inflata size frequency distributions. This was interpreted 0.183mm Fig. Table Cold-Core NO. OF INDIVIDUALS SS=Sargesso SWR= Probability Kendall's Diacria TAXA Limacina L L Cavolinia Clio Creseis Clio Styliola Creseis Limacina L Cavolinia imacina imacina 3 imacina .104 III Size pyramidata cuspidata Rank Slope and0.505mm .156 Corcordance acicula quadridentata distribution virgule subula Rings. order bulimoides retroversa lesueuri trochiformis inflata inflexa immatures Water level Sea; .208 of abundance 6MWCR=6ulf mesh Region; virgula .260 of (0- Limacina .312 ( 6SCCR= 100m, (M) ROA) SWR 8 9. 18. IO. 14. 1 .364 of 9. 6. 3. 7.5 7.5 5. 4. 2. 1. <01 1. of .30 ENVIRONMENT nfght) Mexico trochiformis the 0SCCR MAXIMUM 6ulf 2)(7) (20) .416 top 12. 15. 1 .46 IO. (from - 8. 5. 6. 3. 2. 4. 7. 273 Stream <01 t. 1. 13 Warm-Core .468 - laxa Snider, DIMENSION 20. RF IO. 1 15. (no. by Cold-Core .520 2. 3. 9. 5. .7. 6. 4. 8. 7. 1. <.01 taken 1. .76 environment. 1975). of (22) Rings; .572 simultaneously tows) 14. 13. 4. 2. 16. SS (mm) 8. 5. 6. 3 - 9. <.01 1. .77 Rings; OMWCR .624 OMCCR= - (7) 11. 25. 2. 7. IO. 19. 12. .676 6. RF=Ring 4. 9. 5. 3. <01 1. .56 with 0MCCR Oulf .728 (6) 20. 21. IO. "Bongo" 5. 3. 6. 7. 4. 2. 7. - of <01 1. Fringe; .81 .780 Mexico nets .832 of -274- 03 indicating a slower growth rate in the Sargasso begin to show some explainable patterns. Sea than in the Oulf Stream Cold-Core Rings (Wormuth, 1985). When the food supply In the rings decreased, so did the water column DISCUSSION abundance anomaly of L. inflata. This "opportunistic" species can exploit Oulf Stream Most vertically migrating species showed little Cold-Core Rings and is common in the Slope Water response to differing temperature regimes. Their Region apparently through seeding from Gulf depth distributions are about the same during the Stream Warm-Core Rings (Table III). It same seasons in the different environments maintains a population in the Slope Water Region studied (Fig. 4). Nonmigratory species seem to be except that it apparently cannot survive the more temperature-sensitive in that in new Oulf colder winter months (Vecchione, 1979; Myers, Stream Cold- Core Rings they are very rare or 1967). No other species of euthecosomatous absent. This might be due to the much larger pteropods show this type of population dynamics, temperature range experience by migrators. More not even its congeners. L. inflata has a unique work needs to be done in Oulf Stream Warm-Core type of reproductive behaviour in that it broods Rings to complete this comparison. Most previous embryos and early veligero in its mantle cavity, studies have stressed the similarities in releasing them at 0.066 to 0.068mm dalli & distributions rather than the dissimilarities, Wells, 1973) This behaviour may enhance the particularly at the edges of species’ ranges or of survival of young and is not found in its con adjacent water types such as Sargasso Sea water geners. This could account for Its rapid response and Oulf Stream water or Oulf Stream water and to rings. the Slope Water Region. Modern sampling L imacina trochiformis exhibits a different technology allows fairly high sampling resolution distribution pattern. Although it is a widespread and a greater effort should be concentrated in warm water species, it is very low in abundance these frontal regions. and quite patchy beyond tile influence of boundary Vertically stratified samples should be collected currents (McOowan, 1960). It survives in Oulf on a scale relevant to the species' biology. Stream Cold-Core Rings (while the rings are Crarse-scale sampling (100m intervals) is physically, chemically and biologically more like useful only for determination of where the the parent Slope Water Region than the Sargasso organisms are and whether they migrate or not. Sea) for a much longer period of time than the Samples collected at IO-25m intervals along with cold water species L.retroversa, but at much physical data and synoptic water samples should lower abundances - it ranks second in the Slope help to resolve causative factors from correlative Water Region and seventh in Gulf Stream factors. The species studied were always found at Oold-Oore Rings based on mean abundance (Table shal'ower depths ( M of 14 tows in the Oulf of III). In the Oulf of Mexico L. trochiformis ranks Mexico) than the fluorescence maximum (Fig. 5) eleventh In warm core rings originating from the (when measured) as decribed in other 2ooplenkton Loop Current and second in cyclonic eddies of studies (l.onghurst, 1976; Herman, 1983). A unknown origin in the northwestern Oulf of nine-bottle reck of niskin-type bottles is Mexico. When viewed In the context of the overall presently being built to be mounted on our data base, this high ranking in these cyclonic MOCNESS. Synoptlcally-collected water samples features is quite unusual. Although there is not an could be incubated to examine the relationship analogues mechanism for the formation of cyclonic between vertical distributions and primary features In this area as there is in the Oulf Stream productivity and other aspects of water system, the high ranking of L. trochi form is and chemistry. There are aiso differences in the its shelf-type distribution (Vecchione, 1979) vertical distributions of size frequency structure suggests a shelf origin for the water. When based of species (Fig. 6) which often are undiscernable on sufficient numbers of samples from various by our usual field (mesh size selection previously areas, the differences in rank order of species discussed) and laboratory sampling techniques -275- TEMPERATURE (°C) 100 200 - 300 e X I 400 a. u a 500 600 700 800 Fig. 4 The daytime depth distribution of L imacina inf lala in two Gulf Stream cold-core rings and the surrounding Sargasso Sea) and associated temperature profiles. The vertical lines are the total range; the rectangles are the 25th, 50th end 75th percentiles of each population. Numbers below these lines are */m2. fluorescence (usually time considerations), but which may 1.0______* TEMPERATURE (°C) provide data useful to biogeographic studies by showing that different growth stages are found in different portions of the water column and are therefore in somewhat different environments. Tagging rings using satellite-tracked drifters and sampling them at different stages in their life histories appears to have contributed substantial Inflata insight into the response of pteropod species to their environment (one resident of tile Slope Fig. 5 The night-time depth distribution of the 25th, 50th and 75th percentiles of a strong migrator (Limacina inf/a la) and a non-migrator ( Creseis acicula) in the northwest Gulf of Mexico with associated temperature end fluorescense profiles. Numbers below the vertical lines are #/m2. -276- Physis (A). 42: 25-38. -HAAGENSEN, D. A. . 1976. Caribbean zoo plankton Part ! I-Thecosomata. Off. Naval Res., :712pp. -HERMAN. A.W., 1983. Vertical distribution patterns of copepods, chlorophyll, and production in north eastern Baffin Bay. timnol. Oceanogr., 20 : 709-719. -CALLI, C. M. & F. E. WELLS. 1973. Brood protection in an epipelagic thecosomalous pteropes, Spiratella ('Limacina') inflata (tfOrbigny). Butt. mar. Sei., 23'. 933-941. -LONGHURST, A. R.. 1976. Interactions between zooplankton and phytoplankton profiles in the eastern tropical Pacific. Deep-Sea Pes., 23: 729-754. -MC60WAN, J. A.. 1960. The syei amai/es, distribution and abundance of the Cutheco- somata of the North Pacific. Univ. California, San Diego, Ph. D.Diss.: 212pp. Fig. 6 The size frequency distributions in the -MC6CWAN, J. A., 1971. Oceanic biogeography of the upper 100m in the Sargasso Sea in August 1975 Pacific. In : B. M. Funnel «. W. R. Riedel (eds). The for /. imacina bulimoides. micropaleontology of oceans. Cambridge Univ. Press : 3-74. -MOORE. H. B.. H. B. OWRE, E. C. JONES L T. DOW. Water Region water disappears rather rapidly as 1953. Plankton of the Florida Current. III. The control the environment degrades, one nonresident species of the vertical distribution of zooplankton in the of Oulf Stream Cold-Core Rings "Invades” rather daytime by light and temperature. Bull. mar. Sei., rapidly and grows quickly and most nonresident 3 : 83-95. species populate Oulf Stream Cold-Core Rings -MYERS. T. D., 1967. Horizontal and vertical only very slowly es they become more similar to distribution of thecosomatous pteropoda off the Sargasso See and show no unusual population Cape Natteras. Ph. D. Diss., Duke Univ.: 223 pp. increases). Although direct experiments have not -ROTTMAN, M. L. 1978. Ecology of recurrent groups yet been done, food supply appears to be important of pteropds, euphausiids, and chaetognalhs in the Gulf of Thailand and the South China Sea. Mar. Bio!., 46 (Wormuth, 1985) ss one might have predicted. : 63-78. Further, It appears that chlorophyll per se Is not -SAKTHIVEL. M., 1975. A nota on the annual variation the parameter of prime importance. Short of eulhecosomatous pteropds along the meridian 78' E horizontal tows at depths of high abundances with in the Indian Ocean. Bull. Plankton Soc. Japan, synoptic water samples appear to be a logical step 2t: 41-44. to further define environmental parameters -SAKTHIVEL, M.. 1977. Further studies of piwktcn associated with both high and low concentrations ecosystems in the eastern Indian Ocean. Viii . of individual species. Seasonal, diurnal and latitudinal variations in abundance of Euthecosomata along the 100‘E meridian. Aust. J. mar. freshw. Pes., 26 : 663-671. REFERENCES -SNIDER, J. E. 1975. Quantitative distribution of shelled pteropoda in the 6u!f of Mexico including related sampling studies. Ph. D. Diss. -CHEN, C. & A. W. H. BÉ. 1964. Seasonal Texas AWI Univ.: 211 pp. distributions of eulhecosomatous pteropoda in the -VECCHIONE. M.. 1979. Planktonic moHuscan surface waters of five stations in the western North faunal structure across a larga scala Atlantic. Bull. mar. Sei., /4: 185-220. environmental gradient. Ph. D. Diss., College of -OADON, J. R., 1984. Distribution and abundance of William and Mary: 153 pp. Pteropoda Thecosomata in the southwestern Atlantic. -WIEBE, P. H.. K. H. BURT. S. H. BOYD & A. W. -277- MORTON, 1976. A multiple opening/closing net and environmental sensing system for sampling zoo plankton. J. mar. Pes., 34: 313-326. -WORMELLE, R. L. 1962. A survey of the standing crop of plankton of the Florida Current. VI. A study of the distribution of the pteropods of the Florida Current. Bull. mar. Sei., 12: 95-136. -WORMUTH, J. H.t 1985. The role of cold-core Gulf Stream rings in the temporal and spatial patterns of eulhecosomatous pteropods. Deep-Sea Res., 32 : 773-788. -278- PATTERNS OF PHYTOPLANKTON ABUNDANCE AND BIOGEOGRAPHY CHARLES S. YENTSCH & JEAN C. GARSIDE Bigelow Laboratory for Ocean Sciences, West Boothbey Harbor, USA. INTRODUCTION empirical model) involves using the physiological relationships between photosynthesis and Are the large scale blogeographical distributions respiration in conjunction with physical features of oceanic biology a response to seasonal and such es the depth of the mixed layer and the spatial patterns of primary production? We ask nutrient-density field of water masses. This this question because to us biogeographic approach attempts to portray in one section of the boundaries appear es fences behind which North Atlantic the time and space changes in taxonomists reconcile differences in species. phytoplankton biomass. We will compare this Could it be that indeed the fences are distributions portrayal with biogeogrephic regional boundaries of food resources and thus dictate biogeographic for open ocean myctophi. boundaries? As pointed out by oceanographers Sverdrup 8nd Redfield, geostrophic currents dictate the shape of the density structure. What we SEASONALITY OF "NEW PRODUCTION": THE term the “degree of baroclinicity" is a global CONCEPT. mirror of primary production. The fact is that for at least fifty years we have recognized that We begin with the premise that stirring of the climatological factors (i.e., light, wind, upper layers by convection and wind is a major temperature) regulate phytoplankton growth. We mechanism for regulating primary production. recognize that seasonality in the primary The substrates for phytoplankton growth are light processes for growth are controlled by the and nutrients, and these sre regulated stirring of the upper layers of the oceans and the nutrient-density field which over large scales reflects mass transport of geostrophic currents (Yentsch, 1974; Yentsch, 1982). Why then are we so hesitant to tie the climatological primary process together with concepts concerning biogeogrephy? One answer might be that we simply do not h8ve enough knowledge of primary productivity over large SECTION pi areas of the world's oceans. The global map of productivity prepared from observations by ./ NORTH AT LANTIC KoblenU at al., (1969), does not consider v.. SUBTROPICA seasonal change. With only limited Information of time and space change in primary production one is cöutious to assign substantive relationships with biogeographic boundaries. Throwing caution aside, we have selected a region of the Central North Atlantic (Fig I) to Fig. I North sections modeled in this paper. Heavy predict time and space change in the biomess of lines indicate northern and southern boundary Tor plankton. The scheme of the prediction (an N.Atlantic subtropical populations of myctophids. -279- climatologically by way of the mixing processes of SEMI-EMPIRICAL ANALYTICAL MODEL FOR "NEW the upper layers. Thus the physical feature known PRODUCTION OF PHYTOPLANKTON. as the mixed layer is the region of the ocean which couples climatology (light, wind, temperature) Our modeling efforts require the parameters with processes which regulate phytoplankton shown in Table I (( I ) P:R relationships and (2) growth. nitrate nitrogen in the mixed layer). These data We argue that seasonality in primary are used on a monthly bssis at each 10* latitude. production in time and space is controlled by the The P:R in the mixed layer is taken from equations movement of the sun from equatorial regions (Fig. derived empirically by Yentsch (1981) 2) to higher latitudes until the summer solstice P:R(1-10) = P:R*.Ze/Zfn (I) and then returning to lower latitudes until the when (P:R)* is the optimum ratio (IO) at light winter solstice. This sojourn regulates primary saturation. A P:R= 1.0 indicates no net growth. The production by deepening the euphotic zone (Ze) euphotic depth is calculated by and inducing a shoaling of the mixed layer ( Zm) at Ze = Ln l0-Ln 1e/Kt (2) high latitudes. The situation reverses as the sun retreats to the winter solstice. end the amount of nitrate in the mixed layer is The deepening and shoaling of the mixed layer NaJpM/M2) = 0fZmN03-N . dZ (3) regulates the mean photon flux density reaching a population of nutrient (N^) stirred into the where, NOj - N = pM/kg. mixed layer and describes potential growth, thai The estimate of production of phytoplankton is photosynthesis: respiration (P:R). nitrogen is the product of equtations I and 3, Thus in concert, these are the factors which where P:R is normalized from 0 (no growth) to influence the seasonality and are the basis of our IO (ca. maximum optimal growth). The product empirical modeling which follows. reflects the amount of phytoplankton nitrogen in the euphotic layer. Daily production estimates were obtained by dividing the monthly figures by 30. P:R RELATIONSHIPS IN THE MIXED LAYER Over the north to south section the mixed layer depth ranges between 30 and 900m (Fig. 3). The deepest layers in this section are confined to latitudes higher than 30*N, and the extremes in depth occur at latitudes higher than 40*. At ali latitudes the deepest layers are during winter and spring months (Feb., March, April) and occur at St AV5NM (HANGI rn /, 604N. P R *4 II t ONOI Ilf* AO'W A general rule of thumb is that no phytoplankton Fig. 2 Hypothetical conception of changes in growth can occur if the mixed layer exceeds the parameters in section (Fig. I ) due to movement of euphotic depth by five times (Oran & Braruud the sun from Southern to Northern latitudes. Zm (1935). The euphotic depth (Fig. 3) ranges is mixed layer depth, Ze is euphotic depth. P:R is between 74 and 40m. With deeper mixed layer photosynthetic - respiration ratio, Zm is the depths and shallow euphotic zones at high latitudes nutrient content of the mixed layer. Positions of during winter months, it is apparent that the lines represent parameter distribution during populations at latitudes higher than 40*N are the northern winter. The arrows indicate depth severely light limited a major portion of the year. change es the sun moves to the north. This can be demonstrated by the P:R relationships -2B0- Teble I Parameters for each latitude. Symbol Parameter Units 1. Incident Solar Radiation* coi era'2 d“* Mixed Layer Depth3 Meters z. Euphotic Depth 3 Meters P:R Ratio of Photosynthesis to Respiration * 1 - IO "Zm Nitrate Nitrogen in Mixed Layers |iM/M2 ’Kimball's Tables (1928) 2Robinson, Bauer &Schroeder Atlas ( 1979) 3lnl0 - Lu le/Kt where le is the minimum photosynthetic radiant energy 1.3 cal cm "2 d_,(seeJenkln, 1937). Empirically derived (Yentsch, 1981 ). 5Nzm - NO3-N • dz (Yentsch, 1981 ). NO3-N (pM/Kg) taken from 0E0SEC8 Atlas ( 1981 ). Fig. 3 Seasonal changes in the depth of the mixed Fig. 4 Changes in euphotic depth (Ze). layer (Zm) during winter-spring. north of 40*. 'atiuwn es an example in figure 5. During March, light limitation (low P:R) Is most severe because NITRATE-NITROGEN IN THE MIXED LAYER solar radiation is relatively low and mixing depth near its maximum. It should be noted however We must now demonstrate that changes In mixing from this figure, that the effects of light limit depth control the nitrate content in surface ation are estimated to be observed at ali latitudes layers, but first let us consider the distribution greater than 10*N with the most severe effects of nitrate. Figure 6 shows the vertical distrib- -281- 12000 - 6000 3000 - Fig. 5 Seasonal change in the ratio of photo Fig. 7 The amount of nitrate (pM/M2) Introduced synthesis to respiration ( P:R). to the mixed layer, January through March. ution of nitrate-nitrogen observed in the GEOSECS layer from the equator to 20* N deepened to 400m, transect at these latitudes. The baroclinie effects surface waters would be as rich in nitrate as the of the geostrophic currents are apparent at latitudes north of 40*. latitudes 40*N (Gulf Stream System) and 10*N (Equatorial system). These baroclinie features are important since it is apparent that as mixed SEASONAL CHANGE IN PHYTOPLANKTON layer depths change it will stir different amounts ABUNDANCE AS A FUNCTION OF LATITUDE of nitrate into the upper layers at high latitudes and input large quantities of nitrate into surface Figures 8, 9 and IO show seasonal trends in la/ers( Fig. 7). We can speculate that if the mixed phytoplankton biomass at different latitudes. The Fig. 6 Distribution of nitrate-nitrogen ( pM/kg) from north to south at longitude 40*W. -282- EARIY WINTER SUMMER - AUTUMN Fig. 8 Seasonal change in phytoplankton nitrogen Fig. 10 Seasonal change in phytoplankton nitrogen (PiRxN^) in early winter. (P:R x N £„) between autumn and summer. WINTER - SPRING between latitudes 20*-40*N. The period of winter to spring, i.e. January through May, reflected highest stocks at ali latitudes. Lowest stocks occur during early winter (November and December). Summer through autumn the section is augmented in phytoplankton stocks at latitudes 50* and 60*N. These trends in phytoplankton reflect the background of so-called baroclinie patterns of nitrate distribution shown in figure 6. In essence, they reflect the amounts of nitrate entrained by vertical mixing. The high biomass at high latitudes is because the penetrative mixing has greatly enriched the euphotic layers with nitrate. Low stocks of phytoplankton are conversely the result of a shallow mixed layer and/or a deep nutricline. The most important feature in the Fig. 9 Seasonal change in phytoplankton nitrogen southern region of this section is the influence of (P:R x N^) between winter and spring. tho north equatorial current. The baroclinie features, associated with this current, allow values ( P:R. N Zm) are the product of equations I nitrate in the shallower layers to be reached by and 3. This product is an estimate of penetrative mixing rather than in latitudes phytoplankton nitrogen biomass in the euphotic Immediately surrounding them. zone. If one assumes a 1:1 relationship between nitrate and chlorophyll, the values shown represent euphotic chlorophyll, i.e., the amount THE RELATIONSHIP BETWEEN PHYTOPLANKTON in mgs/M2. STOCKS AND NORTHERN AND SOUTHERN Examination of the trends for ali seasons shows MYCTOPHI BOUNDARIES two regions of high biomass. The highest is at latitudes greeter than 40*N. The next is centered In the Northern Atlantic subtropical region the at IO* north of the equator. Lowest estimates are southern boundaries are the rorth equatorial -283- current, end the northern boundary is the GuH this section. The high production of these regions Stream. Biogeographers, such as Richard Backus is maintained by the geostrophic currents aid the and his colleagues, are aware of the water mass barocllnicity Imparted on the water mass by this differences between the North Atlantic flow. This means that as long as these currents biogeographic regions. We believe our analysis continue to flow in these locations, these regions has demonstrated that the regions could be will continue to occupy their relative status as delineated on the basis of productivity alone. The regions of high productivity throughout this northern regional boundary coincides with the region of the oceans. This leads us to conclude that north limit of the Sargasso Sea and a major change the density nutrient relationships must be in phytoplankton abundance. The southern limits fundamental biogeographic relationships of coincide with the edge of the north equatorial natural oceanic populations. We have observed current and aiso the beginning of a regio-, of good relationships between the ebundance of tuna increasing phytoplankton abundance. Thus the assessed by conventional fishing techniques, and myctophi populations in the center of the North distributions of chlorophyll and primary Atlantic subtropical region are bounded by two production (Yentsch, 1973). Further, the geostrophic fences which form the central gyre of distributions of species of ocean myctophids falls the Sargasso Sea. Myctophids housed within this in the same category, indicating that myclophid gyre must adapt to the relatively low steady-state abundance is correlated with primary production, production which is known to characterize this which in this case is augmented by the effects of region. However, fishes residing at the boundaries ocean currents. That the stability of these regions of these regions, live in much more productive should be tested by satellite images which clearly waters. In these waters, the production of show that the major frontal regions, such as the phytoplankton comes in the form of strong Gulf Stream system, can be monitored from space seasonal pulses. We can ssk whether this region and evaluated in terms of position over large e-eas achieves the greatest myctophi abundance? Is it of the oceans in time. more preferable to reside in the north central Sargasso Sea or in the boundary regions? Scanning the monographs (Nafpaktitls et al., SUMMARY 1977), the distribution of abundance of myctophids appears to show greatest abundance A semi-empirical model of new production around the northern boundary at approximately predicts two major phytoplankton fronts at 40*N. Some abundance occurs at the southern latitude IO* and 40*N. These correspond to the boundary and in some cases species show no northern and southern limits of myctophi geographic preference for any particular part of populations in the biogeographic region of the the region. The strong relationship to northern subtropical North Atlantic Ocean. The persistence boundaries and abundance suggests some unique of these fronts Is due to baroclinie effects of the relationship in temperature and food abundance. It Gulf Stream in the North and the North Equatorial can be postulated that this ideal environment for Current in the South. It is believed that growth and abundance of these fishes occurs in density-nutrient relationships imparted by the frontal gradients. This is certainly not a novel movement of ocean currents must be fundamental suggestion, as many researchers have noted the to the biogeographlc relationships of oceanic distributions of an abundance of fishes populations. concentrated in frontal regions. We believe that the novel information uncovered by our modeling is the apparent geographic ACKNOWLEDGEMENT stability of the regions of relatively high and low phytoplankton abundance. The fact that while these This research was supported by NASA, Office of regions are variable seasonally, they are on the Naval Research and the State of Maine. Bigelow average the sites for high food production over Laboratory Contribution No. 85029. -284- REFERENCES -BAINBRIDGE. A. E.. 1981. 6E0SECS Attentie Expedition. 1. Hydrographic Data 1972-1973. U.S.Govt. Printing Office. *038-000-00491-3. -GRAN, H. H. ê. T. BRARUUO, 1935. A quantitative study of the phytoplankton in the Bay of Fundy and the Gulf of Maine. J. bioi. Bd. Can.. I: 279-467. -JENKIN, P. M„ 1937. Oxygen production by the diatom Coscinodiscus excentricus in relation Io submarine illumination in the English Channel. J. mar. bioi. Asa. U.K., 22: 301. -KIMBALL. H. H.. 1928. Amount of solar radiation that reaches the surface of the earth on the land and on the sea, and methods by which it is measured. Monthly Wea. Rev., 56 : 393-399. -KOBLENTZ-MISHKE 0. J.. V. V. VOLKOVINSKY & J. G. KABANOVA, 1969. Phytoplankton Production Map. In: Alias of the Living Resources of the Seas. F AO UN. Oepl. Fish. Rome. 1972. -NAFPAKTITIS. B. G.. R. H. BACKUS. J. E. CRADDOCK. R. L. HAEDRICH. B. H. ROBINSON &. C. KARNELLA, 1977. Map of Atlantic Ocean faunal regions and provinces. In : Fishes of the Western North Atlantic, Allen Press, Inr., Lawrence, KA,: 270. -ROBINSON, M. K.. R. A. BAUER & E. H. SCHRGEDER. 1979. Allas of North Atlantic- Indian Ocean Monthly Mean Temperatures and Mean Salinities of the Surface Layer. Naval Oceanographic Office N00RP-18. -YENTSCH. C. S„ 1973. Remote sensing for productivity In pelagic fishes. Nature. 244*5415 : 307-308. YENTSCH, C. S., 1974. The Influence of geostrophy on primary production. Tethys, 6( 1-2): III. -YENTSCH. C. S., 1975. Critical mixing depth. In : J. J. Cech Jr. et al. (eds) Respiration of Marine Organisms. Maine vs. Marine Biomed. Symp. : 1-10. -YENTSCH. C. S.. 1982. Satellite Observation of Phytoplankton Distribution Associated with Large Scale Oceanic Cirulation. NATO Sei. Coun.Studies, '4 : 53-59. -YENTSCH, C. S.. 1982. Vertical mixing, a constraint to primary production: an extension of the concept of an optimal mixing zone. In: J. C. J. NIHOUL (ed ). Ecohydrodynamics. Elsevier Oceanogr. Ser. : 67-78. -205- SUMMARY REPORT AND RECOMMENDATIONS R. K. JOHNSON Field huMUM of Naturel History, Chicago, U.S.A. S. VAN DER SPOEL Institute for Taxonomic Zoology, Amsterdam, Um Netherlands INTRODUCTION The very nature of oceans, their vastness and three-dimensional aspect impose considerable It Is perceived thai pelagic biogeography had constraints upon the methods by which we attempt somehow not shared in the renaissance of interest to develop a coherent understanding of the that had occurred In the last decade for shallow- mechanisms involved in determining and water and terrestrial systems. Yet stud/ of the maintaining pattern in biogeographic systems. open ocean, the largest environment on eerth, Repetative sampling over diverse spatial and still relatively unaffected by human activity, tenporal scales is neccessary with the difficulties offers uniquely-interesting opportunities for compounded by the need to use different sampling studies of evolution, separation and maintenance techniques for different organisms. Manipulative of distribution patterns of species and of biotas. experimentation is usually not possible. The organizers of the International Conference Fundamental to biogeograph'/ is good taxonomy and on Pelagic Biogeography attempted to bring good taxonomy depends upon the collection of together active open-oceen researchers geographically adequate samples, aid specimens in embracing the broadest possible diversity of good condition. Ali too often such collections are groups and approaches to discuss the outstanding lacking, due either to inadequate sampling or to questions of open-oceen biogeography, where we the use of inappropriate methods of collection and are, where we ought to be going. The conference preservation. programme was designed around nine topic areas, Expatriation is known to occur, what is not covered in turn by symposium sessions of known is its prevalence and its significance in the presented papers and workshop discussion origin and maintenance of biogeographic patterns. sections. Ontogenetic vertical links and their significance have been largely ignored. TOPIC I. WHAT IS UNIQUE ABOUT PELAGIC BIOGEOORAPHY? TOPIC II. CONGRUENCY OF EPI-, MESO-, AND BATHYPELAGIC PATTERNS Unique features of open-ocean biogeography center around the vastness, the connectedness and Concordonce in distribution among open ocean the three-dimensionality of the open sea. There species of different taxonomic and trophic groups are few geographic barriers and ecotones are often occurs. It is the basis for widely accepted maps of very broad. The recognized faunal regions ara the oceanic species assemblages, faunal regions and largest on the planet. Open ocean biogeographic ecosystems. However, the data that serve as the studies are typically done at the specific and basis for postulated concordance in distribution infraspecific levels as taxa of higher rank (genus patterns have been derived from a multitude of and higher) are typically cosmopolitan (or nearly disparate sources and are often reported in ways so) within the warmwater ocean. In the open see not directly or easily comparable. -at our current state of knowledge- the concepts Maps mirât be constructed using a uniform style of "faunal region" or "community" or "ecosystem" and format, with the same agreed-upon standards verge on being interchangeable- their boundaries for inclusion of positive and negative data The are mapped by recurrent distributional studies. biggest problems involve techniques and scales of -286- sampling that differ by size and nature (e.g. the following areas need attention. problem of the "gelatinous" organisms, see There is a need to look at living, in addition to Harbison, this volume). Interpretation of preserved organisms to gain insight Into morph historical antecedents of current patterns will ological, ecological and behavioral characters involve paleontologie stud/ of historical patterns useful for systematic and biogeographic of organtsmal distribution and the history of understanding. Especially important is the distribution of environmental parameters. Aiso observation of organisms in situ to establish important to interpretation of the origins of behavioural traits relevant to trophic patterns will be meaningful estimates of interactions. Thia is vital to enhancement of our phylogenetic interrelationships. It seems clear understanding of community structure as that studies on closely-related species pairs ma/ determined by coactive effects and biological contribute to our knowledge of the nature and accomodation. origin of biogeographic boundaries. Difficulties in sampling large and small organisms on the same scales are evident but must be adressed by improvements of sampling TOPIC III. POPULATIONS, PATCHES OR CLUSTERS: tecniques. THEIR ROLE IN PELAGIC BIOGEOGRAPHY There is a great need to develop new instruments and techniques to address relevant Genetic populations are considered to consist of questions In population structure, genetics, scales groups of organisms within which gene flow is of distribution and so forth. relatively unrestricted. Ecological populations are groups of organisms with similar demographic, morphological and/or behavioural character TOPIC IV. VARIATION AND THE SPECIES CONCEPT istics. IN OPEN-OCEAN PLANKTON AND NEKTON It has not been shown whether different ecological populations (mesopelagic fish, selps, It was strongly felt that progress in open-oceen decapods) ara in fact different genetically- This work will neccessitate e greater infusion of might have important blogaographlc consequences modern systematic theory, particularly In in terms of divergence and spéciation. available approaches to the estimation of It would be of value to determine if centers of phylogeny. abundance are the same (spatially and/or There have been very few attempts for oceanic temporally) as centers of populations in either organisms to utilize cladistic or numerical or the genetic or ecological sense (cf. Merretti de other modern methods, singly or in combination, Visser; Domanski, ali in this volume). Knowledge to produce results based on the greatest possible of this would be presumably be important to the fraction of the available dete. There appears to be understanding of boundaries. Open-ocean no fundamental difference In our concept of what biogeographic maps are essentially boundary constitutes a species between oceanic vs plots, typically based on presence/absence data terrestrial systems. Clear definition of the (or, for some groups, charts of relative species concept is essential to open-ocean work abundance), no open-oceen species can be mapped because it is at the species level that open-oceen at the population level. Genetic studies seem biogeographic work is done. prerequisite io aquisition of such ability. Recognition of species or of genetically distinct The concept of communities is based on the entities in the ocean may be retarded by the co-occurrence of species, the Inherent assum tendency to regard the oceans as an environment ption is one of co-adaptation. The coadaptation of with weak or non-existent barriers to gene flow, species in communities may be expressed most when in fact we know next to nothing about gene clearly in trophic relationships. flow in open ocean systems. Throughout this session a recurrent theme Contributing as well is-the fact that there have involved sampling difficulties. In particular the been very few studies of variation within broadly -287- distributed species. Such studies of population were discussed with the novel idea that dispersal structure within broadly distributed species will may in some respects represent the long-term contribute much to our understanding of both what and vicariance the short-term process. constitutes an open-ocean species and of the A number of modes of vicariance were reality of biogeographic provinces and boundaries discussed, eg. orogeny of land barriers, oxygen as defined by congruent distribution patterns. minima, gecial cycles in the Mediterranean. Taxonomic results will likely lie on a continuum A central question involves how to study between recognition of polytypic species "hydrotectonic" events. There was some agreement (Johnson, this volume) to the identification of that the water mass system is, perhaps distinct new forms (Gibba, this volume). analogously, a tectonic system of its own, directly Allozyme and other genetic studies have shown affecting pelagic biotic distribution to a much that the potential for genetic differentiation is greeter extent than more remote plate tectonics present and operating in the deep see and that processes and events. genetic differences occur over short distances. In Identified sources of clarification include areas a few hundred square kilometers, distinct syntheses of knowledge of modern organismal and populations of some organisms have been water mass distribution patterns with historical recognized. information/inference based on phylogenetic and The biological mechanisms leading to and paleontologie studies. maintaining reproductive isolation in open-ocean organisms are virtually unknown because (in part) of the great difficulties involved in working TOPIC VI. VERTICAL DISTRIBUTION: STUDY AND with living forms. Greatly needed are additional IMPLICATION biochemical, behavioural and physiological studies, breeding experiments, and life history Vertical segregation of close-related species can information. result in allopatric ranges at a single geographic Differ ences in generation time may lead to a position. vastly different interpretation of distribution 8s There is a relationship between the scales of a function of spatial and temporal scales. horizontal distribution patterns with depth. The At ali times reciprocal study of the interaction scales increase with increasing depth, but this between organisms and their environment are relationship may break down in the benthopelagic. needed in behavioural and distributional ex Sampling must adequately cover the full planation. vertical range, otherwise vertical vs. horizontal distribution patterns cannot be described. It is important to emphazise the effect of TOPIC Y. VICARIANS BIOGEOGRAPHY sampling scale. If sampling is conducted within a limited area, the vertical zonation pattern Communities and the ecological relationships appears to be clearly-related to depth-correlated defining them aiso have histories which might be parameters. At larger sampling scales, the elucidated partially by the fossil record where it influence of gross circulation patterns, as possible, for example, to perceive dominance. A indicated by the water mass structure of the water potential major contribution of systematica, column, becomes more apparent. namely knowledge of phylogenetic relationships, Differential ontogenetic vertical migration has direct relevance to historical questions. patterns appear to be strongly correlated with An Important problem Is that our present available food supply. Such differences are often estimate of taxonomic differentiation may in fact magnified in horizontal distribution patterns. constitute significant underestimation for some Larval and adult ranges are often different with taxa. Resolution will require additional study and the larvae more sténotypie. Such patterns appear advances in concept and technology. to be part of the linkages between overall Questions of short- versus long-term processes productivity, particle-size spectra and ecological -208- adaptations with depth. histories such an understanding is not possible. One question adressai was the reality of Vital is the recognition that not ali life history spéciation within oxygen minimum regions. stages are congruent In distribution and that Evidence was discussed for the existence of organisms in different stages of their life history specialized endemics with highly-restricted will have different requirements. Unknown or horizontal ranges within regions defined by a uninterpreted differences in morphology at well-developed oxygen minimum. Widespread different stages, not to mention differences in distribution of sapropels in both on- and physiology, behaviour, length of time at different off-shore deposits implies that in the past, deep stages, periodicity of reproduction, dispersal oceanic waters were frequently stagnant for long mechanisms, ali may add to act or interact to periods of time. Such conditions may have greatly affect spatial and temporal distribution patterns. modified horizontal distribution patterns. It was aiso noted strongly that plankton samples Since any organisms which fail to synchronize exist whose usefulness has not fully been their cycle with the circulation characteristics exploited and in some studies could allow would get lost from the system, this could avoidance of repetition of expensive field conceivably result in sufficient separation of programs. synchronized and asynchronized populations to result in differentiation. However, it is unlikely TOPIC VI11. BOUNDARIES AND TRANSITION ZONES that ali such vertical migrations are or can be tuned to smaller-scale circulation cells because ( f As used In the following, "transition zone" Is taken the unpredictable variability of the cells. to denote an area superimposed between two regions defined in terms of their physics, i.e. subtropical or subarctic gyre, or between species TOPIC VII. THE ROLE OF LIFE-HISTORY assemblages recognized on congruency within and STRATEGIES species distinction between such areas. It Is important to note that most such zones in the Studies of life histories of pelagic species must literature correspond to physical transitions or include field observations of natural populations frontal zones, e g. between gyres or between gyres to define both the spatial and temporal and circumpolar current regions. The biological distribution of a species. This may be enhanced conception and identification of such zones is badly through laboratory experimentation and the blurred by the non-synoptic data sets typifying development of mathematical models. oceanic biological sampling and established Evolutionary life-history theory may provide collection data basis. models to explain the adaptive significance of In regard to species these regions tend to life-history patterns. contain representatives from the regions bounding Needed are models involving both ecological and ft and Its own set of endemics as well. evolutionary time. Especially interesting might be It is deer that the boundaries between regions models of life history strategies in "cold vs. will depend on the criteria used in their warm" ecosystem areas, elucidating benefits of definition, varying for example as to whether a alternation of generations, relationship between percentile curva, physical indicator or maximal life history parameters and abundance and size of distribution contour is chosen. It was proposed distributional range, or net production as a that to establish the "ranga" of an organism, its balance between fecundity and dilution. reproductive range is the "true" one. The study of biogeography should not only The nature of rings with their Identifiable, document present geographic distribution ling-lived character, and their close analogy to patterns, whether of species or faunas, but aiso other frontal features makes them a natural site lead to an understanding about how such patterns for process-oriented studies of biogeographical have come about. Without the study of life boundaries. -209- The strong link In the biological nature of GENERAL CONCLUSIONS ------O frontal boundaries is perhaps strongly tied to the phytoplankton standing crop and its species (1) Pelagic biogeography is the study of the composition on either side of a front. A fuller distribution of organisms in the largest understanding of the special advective/diffusive environment available to life on earth, the open regime associated with frontal boundaries and its ocean. Its study involves not only the pelagic effect on various types of organisms represents an realm but connections with adjacent systems. The essential goel for ecological understanding of open ocean is continuous with coastal systems at open-ocean biogeography. its boundary and any understanding of either ultimately depends upon study of both. The open see is linked with the atmosphere via air/sea TOPIC IX. THE ROLE OF REGIONAL AND TEMPORAL Interactions, with organisms serving as an index VARIABILITY IN PRIMARY AND SECONDARY to and in certain cases actually influencing PRODUCTIVITY interaction. Further, the open ocean is linked with bottom processes; sedimentation, recirculation, Major geographic boundaries are formed by and thermal vent processes link bottom and processes associated with, 1) the general benthos with the pelagic. As a system that is (and circulation of the oceans; and ?) seasonal effects has been) essentially physically continuous over which influence vertical mixing at upper layers. time, the open ocean offers unique opportunities Major distribution patterns mirror major for studies ranging from the separation of current patterns. Current mark areas of rapid populations to the development and maintenance of changes in primary productivity. separable communities and ecosystems. Perhaps Large incremental bursts of production in no other system is there a better opportunity to characteristic of high latitudes favour a pattern of employ, and thereby help better define, both energy flow that is different from some low ecologies) and historical approaches to latitude regions where the rate of primary biogeography. Of great Importance to this will be production approaches steady state. It seems not enhanced opportunities to relate modern unlikely that the main determinant of distribution distribution patterns with patterns and changes patterns is food supply, tempered by seasonality. reed from the microfossll record. This working group proposed that the marine 2) Understanding modern and past distribution science community should attempt to test this patterns of pelagic organisms and communities hypothesis. requires understanding of and input from Priority should be given to expanding our virtually ali of the open ocean sciences. The very presently limited knowledge of variation in complexity of the subject tias contributed to a primary production levels and such potentially general lack of rigor in paradigm development, ecosystem-defining parameters as phytoplankton but in a very reel sense pelagic biogeography particle size Speira across regions and should and can represent a general syntheses of boundaries. open-oceen biological study. The value of The group unanimously agreed that a program of interaction among specialists in diverse areas at research of this sort would involve synergistic the conference became absolutely clear to ali. efforts of both pelagic biogeographers and modern Continued community Interaction and periodic marine ecologists. meeting was strongly advocated. 3) Whether the study be called taxonomy or systematica, it is clear that the composition of open-ocean faunas and the structure of broadly-distributed species needs intensive additional, practical and theoretical study. Our basic taxonomic knowledge of many oceanic taxa is -290- wœfully incomplete. The conference advocated zones. To test and refine this hypothesis whole synoptic (as opposed to merely regional) ecosystem studies in gyre boundary zones are systematic studies utilizing both traditional and needed. more recently developed approaches, including 6) Additional mapping studies are clearly genetic/biochemical methodologies, cladlstlc and necessary. Equally necessary is the recognition of vicariance biogeographic models, and more the treasure house of recoverable information in emphasis on living organisms, whether in situ or existing plankton and fish collections and in culture. associated cruise/ capture/ locality information. 4) Sampling remains a continuing most serious The conference advocated community-wide effort problem in open-ocean distributional studies. at "institutionalization" of existing collections This follows directly from the unique expanse of through survey and through establishment of the pelagic environment. It relates as well to disciplinary awareness and standards. short-term instabilities of that environment that 7) Other initiatives/efforts/studies identified vary by location, time and season, and to different by more than one workshop group included: scales of size, mobility and "catchability" of the (a) the great need for additional synoptic study fauna. Use of varied collecting equipment and of broadly-distributed oceanic species, are they methods is required for estimation of sny panmictic or polytypic, what is the nature and significant fraction of the community. Synoptic source of subdivision, how does subdivision relate sampling of biotic material and abiotic data are to recognized ecosystem boundary zones?; additional requirements. Adequate collecting (b) to really understand distribution patterns equipment and preservation techniques are in any given group there must be a essentially unavailable for some of the very greatly-expanded emphasis on life-history fragile (e.g. gelatinous) but wide-spread and studies involving field, laboratory and theoretical ecologically important groups. Greater effort approaches: this is true for ali open-ocean taxa must be devoted to development of such equipment although clearly some taxa are less amenable to and techniques. Continued gear development is such study with currently available methodologies greatly needed, but equally needed are motivated than others; and and rigorous studies of sampling theory and design (c) the potentially important benthopelagic/ applicable to open-oceen systems and questions. pelagic interaction zone is extremely poorly 5) Pelagic biogeographers are fascinated by known and deserves greater attention. boundaries and understandably so, for correlated ------O change in boundary zones offers greet possibilities for understanding causation of open-ocean distribution patterns. Studies of congruency of distribution patterns should lead to better understanding of community structure and the reality of coadaptation. It should likewise leed to knowledge of edge effects and differences in dispersion in and near boundary zones. Vertical distribution studies across ecosystem boundaries should reflect life history and trophic adaptation to unique ecosystem properties. One workshop group advocated the hypothesis that close correspondence between major distribution patterns and large-scale current patterns is related to marked change in productivity and productivity-related properties (such as particle size spectra) thai occur across major current -291- SPECIFIC RECOMMENDATIONS------# It Is recommended that an ad hoc working group be established to survey, compile and publish a directory of existing plankton collections and their resources. It is recommended that contact be made with organizers of the World Ocean Circulation Experiment for possible biogeographic-study- related expansion of the biological program. It Is recommended that the conference organ izing committee study the appropriateness of seeking establishment of a SCOR working group on pelagic biogeography. The work of this group would involve international collaborative efforts involving each of the general conclusions/ recommendations summarized above and such others as the working group or community might generate. It is recommended that the conference organizing committee remain in contact for the possible establishment of an additional or periodic international meeting of scientists working on the biogeography of pelagic organisms. -292- LIST OF PARTICIPANTS TADE H. CASWELL University Museum, University of Tokyo, Hongo, Woods Hole Oceanographic Institution, Tokyo 113, Japan Woods Hole, Ma 02543, U.SA W. ADMIRAAL P.CHANDRAMOHAN Biologisch Centrum, University of Orontngen, Andhra University, Dep. Zoology, Waltair, Postbus 1 4, 9750 AA Haren, the Netherlands Visakhapstnam 530 003, India M.YANGEL D.M.COHEN Institute of Oceanographic Sciences, Wormley, Los Angeles City Museum of Natural History,900 Oooalmlng, Surrey 5U8 6UB, United Kingdom Exposition Blvd, Los Angeles, Ca 90007, U.SA M.BAARS G.R.CRESSWELL Netherlands Institute for Sea Research, SCIRO Marine Laboratories, Div. Oceanography, Postbus 59,1790 AB Den Burg, the Netherlands Sostra/ Esplanade, Hobart, Tasmania, Australia R.H.BACKUS B.DALE Woods Hole Oceanographic Institution, University of Oslo, Dept. Geology, Woods Hole, Ma 02543, U.S.A. Postboks 1047, Blindern, Oslo 3, Norway J.BADOOCK P.DOMANSKI Institute of Oceanographic Sciences, Wormley, Institute of Oceanographic Sciences, Wormley, Oodslming, Surrey 5U8 6UB, United Kingdom Godaiming, Surrey 5U8 6UB, United Kingdom I. BALL MAFERNANDEZ ALAMO Memorial University Newfoundland, Univ. Mexico UNAM, Lab. Invert. Fee. Ciencias, St. John's, Newfoundland A1B 3X9, Canada Apdo Post 70-371,04510 Mexico D.F., Mexico D.BLASOO A.FLEMINGER & J.FLEMINGER Bigelow Laboratory for Ocean Science, McKnown Scripps Institution of Oceanography, Point, W. BoothbayHarbor, Maine 04575, U.S.A. Lajolla, Ca 92093, U.SA D. BOLTOYSKOY R.H.GIBBS Univ. Buenos Aires, Fee. Ciencias naturales, Ciud. U.S. national Museum, Smithonlan Institution, Unlversldad Nunez, 1428 Buenos Aires, Argentina Div. Fisheries, Washington D.C. 20560, U.SA E. BRINTON I. GOTJÉ Scripps Institution of Oceanography, Org. Adv. Oceanogr. Res., SBNO, Postbus 16915, Lajolla, Ca 92093, U.SA 1001 RK Amsterdam, the Netherlands A.BUCKLIN R.L.HAEDRICH College of marine studies, University of Delaware Memorial University of Newfoundland, Lewes complex, Lewes, Delaware 19956, U.S.A. St. John's, Newfoundland A1B 3X9, Canada J. P.CASANOVA R.HALLIDAY Université de Provence, Lab. Biologie animale, Bedford Institute of Oceanography, Marine Place Victor Hugo, 13003 Marseille, France Fisheries Div., Dartmouth N.S. B2Y 4A2, Canada -293- S. HAMILTON H.C.JOHN Scripps Institution of Oceanography, Biologische Anstalt Helgoland, Notkestrasae 31, Lajolla, Ca 92093, U.SA. D-200 Hamburg, FRO G.R.HARBISON R. K.JOHNSON Woods Hoia Oceanographic Institution, Grice Marine Biological Laboratory, 205 Fort Woods Hole, Ma 02543, U.SA Johnson Road, Charleston, SC 29412, U.SA E.O.HARTWIQ S. K.KATONA Office Naval Research, Oceanic Biology Program, College of the Atlantic, Bar Harbor, 800 N. Quincy Street, Arlington Va 22217, U.S.A. Maine 04609, U.SA Q. R.HASLE T. KIKUCHI University of Oslo, Adv. Marin Botanikk, Ocean Research Institute, University of Tokyo, Postboks 1069, B Under n 0316, Oslo 3, Norway 1-15-1 .Minemidei,Nakano-ku,Tokyo 164, Japan R. L.HAURY B.KIMOR Scripps Institution of Oceanography, Techo ion, Institute of Technology, La Jolla, Ca 92093, U.SA Haifa 32000, Israel T. L.HAYWARD AKLEINE Scripps Institution of Oceanography, Free University , Dept. Geology, Postbus 7161, La Jolla, Ca 92093, U.SA 1007 MC Amsterdam, the Netherlands Y.HERMAN J. C.KREFFER Washington State University, Dep. Geology, Netherlands Council Sea Research, Postbus Pullman, Wa 99164-2814, U.SA 19121, 1000 GCAmsterdam, the Netherlands P.J.HERRING D. KROON Institute of Oceanographic Sciences, Wormley, Free University, Dept. Geology, Postbus 7161, Oodalming, Surrey 5U8 6UB, United Kingdom 1007 MC Amsterdam, the Netherlands R.P.HEYMAN K. LANGE Netherlands Institute for Sea Research, Univ. Buenos Aires,, Fac. Ciencias naturales, Ciud. Postbus 59,1790 AB Den Burg, the Netherlands Universided Nunez, 1428 Buenos Aires, Argentina P.HILGERSOM V.J.LOEB Org. Adv. Oceanogr. Res., SBNO, Postbus 16915, Moss Landing Marine Laboratories, P.O. Box 223, 1001 RK Amsterdam, the Netherlands Moss Landing, Ca 95039, U.SA K.HULSEMANN M. MADHUPRATAP Biologische Anstalt Helgoland, Notkestrasae 31, National Institute of Oceanography, Dona Paula, D-200 Hamburg, FRO Goa 403 114, India T.IWAMI N. MARCUS University Museum, University of Tokyo, Hongo, Woods Hole Oceanographic Institution, Tokyo 113, Japan Woods Hole, Ma 02543, U.SA -294- N.B.MARSHALL P.R.PUOH 6 Park Lana, Saffron, Waldon, Essex, Institute of Oceanographic Sciences, Wormley, United Kingdom Qodalmlng, Surrey 5U8 6UB, United Kingdom J.MAUCHLINE F. REID Dunstaffnage Marine Research Laboratories, P.0. Scripps Institution of Oceanography, Box 3, Oban, Argyll, Scotland, United Kingdom Lajolla, Ca 92093, U.SA JAMcOOWAN J. L.REID Scripps Institution of Oceanography, Scripps Institution of Oceanography, Lajolla, Ca 92093, U.SA Lajolla, Ca 92093, U.S.A. I.MELCHER P.H.SCHALK Org. Adv. Oceanogr. Res. SBNO, Postbus 16915, Inst. Taxonomic Zool., Univ. Amsterdam, Postbus 1001 RK Amsterdam, the Netherlands 20125,1000 HC Amsterdam, the Netherlands N. R.MERRETT R.S.SCHELTEMA Institute of Oceanographic Sciences, Wormley, Woods Hole Oceanographic Institution, Qodalmlng, Surrey 5U8 6UB, United Kingdom Woods Hole, Ma 02543, U.SA V. R.NAIR C-tSHIH Nat. Inst. Oceanogr., Regional Centre, Soa Shell, National Museum Natural History, Seven Bungalows, Versova, Bombay, India Ottawa, Canada O. J.NELSON R. SLUYS Mus. natural History, Dep. Ichth., Central Park Inst. Taxonomic Zool., Univ. Amsterdam, Postbus W. at 79th Street, New York, NY 10024, U.SA 20125, 1000 HC Amsterdam, the Netherlands L. NEWMAN I. SPRON0 University of Queensland, Dept.Zoology, St Lucia, Inst. Taxonomie Zool., Univ. Amsterdam, Postbus Queensland 4067, Australia 20125,1000 HC Amsterdam, the Netherlands D.B.OLSON K. J.SULAK Rosenstiel School Marine Science, 4600 Rickenb. Institute of Oceanographic Sciences, Wormley, Causeway, Miami, FI 33149-1098, U.SA Oodalmlng, Surrey 5U8 6UB, United Kingdom M. OMORI J. THIEDE Tokyo University of Fisheries, 4-5-7 Konan, Qeol.-Palaeontol. Inst. Mus., Christ.-Albr. Univ., Mineto-ku, Tokyo 108, Japan Olhausenstrasse 40-60, D-2300 Kiai, FRO T.PAFORT-vanIERSEL D.O.TROOST Inst. Taxonomic Zbol., Univ. Amsterdam, Postbus Marine Science Division, UNESCO, 20125,1000 HC Amsterdam, the Netherlands 7 Place de Fontenoy, 75700 Paris, France A.C.PIERROT-BULTS S. VAN DER SPOEL Inst. Taxonomic Zool., Univ. Amsterdam, Postbus Inst. Taxonomic Zool., Univ. Amsterdam, Postbus 20125, 1000 HC Amsterdam, the Netherlands 20125,1000 HC Amsterdam, the Netherlands 295- J.C.von YAUPEL KLEIN University of Leiden, Dept. Systematic Zoology, Postbus 9517,2300 the Netherlands J.E.de VISSER Org. Adv. Oceanogr. Res., S8N0, Postbus 16915, 1001 RK Amsterdam, thj Netherlands E.L.VENRICK Scripps Institution of Oceanography, Lajolla, Ca 92093, U.SA. J.H.WORMUTH Texas A & M University, College of Geosciences, Oollege Station, Texas 77843-3146, U.SA. C.YENTSCH Bigelow Laboratory for Ocean Science, McKnown Point, W. Boothbay Harbor, Maine 04575, U.S.A. C. S. YENTSCH Bigelow Laboratory for Ocean Science, McKnown Point, W. Boothbay Harbor, Maine 04575, U.SA B.J.ZAHURANEC Office Naval Research, Oceanic Biology Program, 800 N. Quincy Str., Arlington, Ya 22217, U.SA J.ZIJLSTRA Netherlands Institute for Sea Research, Postbus 59, 1790 AB Den Burg, the Netherlands UNESCO TECHNICAL PAPERS IN MARINE SCIENCE Titles of numbers which are out of stock No. Year SCOR No. Year SCOR WG WG 1 Incorporated with Nos. 4, 8 and 14 in No. 27 1965 WG IO 14 Incorporated with Nos. 1, 4 and 8 in No. 27 1970 WG IO 2 Report of the first meeting of the joint group 15 Monitoring life in the ocean, sponsored by of experts on photosynlhetic radiant energy SCOR, ACMRR, Unesco, IBP/PM 1973 WG 29 held at Moscow, 5-9 October 1964. Sponsored by Unesco, SCOR and IAPO 1965 WG 15 16 Sixth report of the joint panel on oceanographic tables and standards, Kiel, 24-26 January 1973; 3 Report on the intercalibration measurements sponsored by Unesco, ICES, SCOR, IAPSO 1974 WG IO in Copenhagen, 9-13 June 1965. Organized by fCES 1966 — 17 An intercomparison of some current meters, report on an experiment of Research Vessel 4 Incorporated with Nos. 1,8 and 14 in No. 27 1966 WG IO Akademic Kurchatov, March-April 1970, by the Werking Group on Current Velocity Measurements; 5 Report of the second meeting of the joint sponsored by SCOR, IAPSO, Unesco 1974 WG21 group of experts on photosynlhetic radiant energy held at Kauizawa, 15-19 August 1966. 18 A review of methods used for quantitative Sponsored by Unesco, SCOR, IAPO 1966 WG IS phytoplankton studies; sponsored by SCOR, Unesco 1974 WG 33 6 Report of a meeting of the joint group of experts on radiocarbon estimation of primary 20 Ichthyoplankton. Report of the CICAR Ichthyo- production held at Copenhagen, 24-26 October plankton Workshop-Afro published in Spanish 1975 — 1966. Sponsored by Unesco, SCOR, ICES 1967 WG 20 21 An intercomparison of open sea tidal pressure 7 Report of the second meeting of the Committee sensors. Report of SCOR Working Group 27; for the Check-List of the Fishes of the North “Tides of the open sea" 1975 WG 27 Eastern Atlantic and on the Mediterranean, London, 20-22 April 1967 1968 _ 22 European sub-r co-operation in oceano graphy. Report ui ii ui king Group sponsored 8 Incorporated with Nos. 1, 4 and 14 in No. 27 1968 WG IO by the Unesco Scientific Co-operation Bureau for Europe and the Division of Marine Sciences 1975 — 9 Report on intercalibration measurements, Leningrad, 24-28 May 1966 and Copenhagen, 23 An intercomparison of some currents meters, III. September 1966; organized by ICES 1969 — Report on an experiment carried out from the Research Vessel Atlantis 11. August-September 10 Guide to the Indian Ocean Biological Centre 1972, by the Working Group on Continuous (IOBC), Cochin (India), by tl.e Unesco Curator Velocity Measurements; sponsored by SCOR, 1967-1969 (Dr. J. Tranter) 1969 — IAPSO and Unesco 1975 WG21 11 An intercomparison of some current meters, 24 Seventh report of the joint panel on oceano report on an experiment at WHOI Mooring Site graphic tables and standards, Grenoble, "D”, 16-24 July 1967 by the Working Group on 2-5 September 1975; sponsored by Unesco, Continuous Current Velocity Measurements. ICES, SCOR, IAPSO 1976 WG IO Sponsored by SCOR, LIAPSO and Unesco 1969 WG21 27 Collected reports of the joint panel on oceano 12 Check-List of the Fishes of the North-Eastern graphic tables and standards, 1964-1969 1976 WG IO Atlantic and of the Mediterranean (report of the third meeting of the Committee, Hamburg, 28 Eighth report of the joint panel on oceano April 1969) 1969 — graphic tables and standards, Woods Hole, U.S.A., sponsored by Unesco, ICES, SCOR, 13 Technical report of sea trials conducted by the IAPSO 1978 WG IO working group on photosynthetic radiant energy, Gulf of California, May 1968; sponsored 29 Committee for the preparation of CLOFETA- by SCOR, IAPSO, Unesco 1969 WG 15 Report of the First meeting, Paris, 16-18 January 1978 1979 _ 30 Ninth report of the joint panel on oceanographic tables and standards, Unesco, Paris, 11-13 September 1978 1979