The Azores Hydroid Fauna and Its Origin, with Discussion of Rafting and Medusa Suppression

THE AZORES HYDROID FAUNA AND ITS ORIGIN, WITH DISCUSSION OF RAFTING AND MEDUSA SUPPRESSION

PAUL F. S . CORNELIUS

CORNELIUS, PAUL F.S. 1992. The Azores hydroid fauna and its origin, with discussion of rafting and medusa suppression. - Arquipe'lago. Life and Earth Sciences 10: 75-99. Angra do Heroismo. ISSN 0870-6581. An international study of Azorean coastal benthos, especially of that around Faial island, has added ten hydroid species to the faunal list which now totals about 70 species depending on taxonomic opinion. The species newly recorded are: Tubulan'a crocea, T. indivisa, Eudendrium sp., Bougainvillia sp., Silhouetta uvacarpa, Laomedea calceolifera, Amphisbetia operculata, Diphasia cf. attenuata, Ventromma halecioides and Aglaophenia picardi. The nature and zoogeographic origin of this limited hydroid and hydromedusa fauna are discussed in relation to ocean currents and other environmental factors. The shallow-water fauna has a high proportion of hydroid species lacking a medusa stage. Their recruitment to the Azores is likely to have been through transoceanic rafting. Further, most of the locally recorded hydroids which do have a medusa stage are known to raft. Possibly no shallow-water Azorean hydroid has become established in the archipelago by means of a medusa stage liberated on a mainland continental coast. Winter storms and browsing by subtidal fish are considered important factors in limiting Azorean hydroid populations. A recognisable group of rafting hydroid species, some having and some lacking a medusa stage, occurs on oceanic islands around the world. The concept of "species club" is introduced to embrace this phenomenon.

CORNELIUS, PAUL F.S. 1992. A fauna de hidr6ides dos A~ores,sua origem e discuss20 sobre a deriva e a supress20 da fase medusa. - Arquipdago. CiCncias da Natureza 10: 75-99. Angra do Heroismo. ISSN 0870-6581. Um estudo internacional do benthos wsteiro dos Aqores, especialmente daquele ao redor da ilha Faial, permitiu adicionar dez novas especies de hidr6ides B lista faunistica, a qua1 totaliza agora setenta esp6cies dependendo da linha taxon6mica adotada. As novas ocorrEncias regionais sb: Tubularia crocea, T. indivisa, Eudendrium sp., Bougainvillia sp., Silhouetta uvacarpa, Laomedea calceolifera, Amphisbetia operculata, Diphasia cf. attenuata, Ventromma halecioides e Aglaophenia picardi. A natureza e a origem zoogeogrifica da limitada fauna de hidr6ides e de hidromedusas sbdiscutidas em relqgo Bs correntes ocelnicas e a outros fatores ambientais. A fauna de kguas rasas,tem uma alta propor@o de especies de hidr6ides nas quais a fase de medusa est.6 ausente. E provivel que o seu recmtamento para os Agores tenha ocorrido atraves de deriva trans-ocelnica. Alem disso, a maioria dos hidr6ides, reportados para o local, que possuem uma fase de medusa, derivam. Possivelrnente, nenhum hidr6ide a~oriano de kguas rasas, se estabeleceu no ArquipBlago, atraves de um estado de medusa proveniente da zona costeira continental. As tempestades de Inverno e o facto de serem aliment0 dos pekes da reg& infralitoral s5o considerados importantes factores na limitqb das pop~la$deSdos hidr6ides a~orianos. Um grupo reconhecido de espkies de hidr6ides derivantes, alguns com e outros sem o estado de medusa, ocorre em ilhas oceibicas ao redor do mundo. 0 conceit0 de "species club" e introduzido para explicar este fenhmeno.

Paul F.S. Cornelius, Department of Zoology, The Natural History Museum, London SW7 5BD, England.

Contribution No. 10 from the "Expedition Azores 1989" INTRODUCTION

'The marine invertebrates of the Azores ate apparently quite poorly known and no reliable data could be found' (BRIGGS 1974: 208). their dispersive capability. The necessary analysis of which species have this capability has not been New records of hydroids collected during a study done, though many that do are coastal forms of Azorean coastal benthos - "Expedition Azores which may not be adapted to open-oceanic condi- 1989, are presented and analyzed along with pre- tions: not least plankton den&. The basic hy- vious local records of the group. The parent inves- dromedusan life cycle comprises a succession of tigation sought to document and describe the planula, hydroid and hydromedusa (often simply benthic biota to a depth of ca. 30 m. Plankton was termed 'medusa'). But in some thirty-five per cent not especially collected. The present account is of the genera and perhaps half the species the me- based largely on material gathered during the dusa stage never leaves the parent hydroid colony author's secondment to this joint study. Speci- and is not dispersive (see p. 91). The planulae of mens collected have been deposited either in the most species are considered to be lecithotrophic Departement of Oceanography and Fisheries, and hence short lived, probably settling after a Horta [DOPH],Faial, University of the Azores, or matter of hours to a few days. Most hydrozoan in the Zoology Department, The Natural History planulae contrast with those of anthozoans many Museum, London, [BMNH;registration series of which are said to be larger and longer lived, 1990.5.2.1-281. More details about "Expedition planktotrophy being widely recorded among pla- Azores 1989" can be found in MARTINS& al. nulae of the latter group (WERNER1984: 50). Fur- (1992). ther, it seems that most coastal hydromedusae live Biogeographically the Azores archipelago is for only a few weeks (RUSSELL1953) and would interesting for several reasons. The islands are similarly be unable to make a long oceanic cross- young and remote, being formed from volcanic ing (RALPH 1961c; KRAMP 1968; CORNELIUS activity connected with the Mid-Atlantic Ridge. 1981,1990b). Analysis of the remote Azorean hy- They rise steeply from the surrounding undulating droid fauna .,contributes to an understanding of abyssal plain which is mostly 1000-2000 m deep. how this group disperses across such distances. The relevant prevailing ocean currents mostly The widely distributed pelagic Porpita and Ve- tend not to cross directly from the nearest land lella, which have a conspicuous floating hydroid masses, considerably increasing the geographic stage, often occur in the Azores. Although they re- isolation of the islands (NAVALINTELLIGENCE DI- lease a typical hydromedusa the neustonic way of VISION 1945; HYDROGRAPHICDEPARTMENT e.g. life of their hydroid stages is exceptional. They 1953; summaries of various aspects in GOFAS are not mentioned further. 1990, BIGG1990 and publications cited therein). Hydroids and medusae are jointly referred to Identification of the Azores hydroid and hydrome- as leptolids, a little-used term discussed elsewhere dusa fauna is considered elsewhere (CORNELIUS (CORNELIUS1990b). The authorities for scientific in press). names of species mentioned are given in an Ap- The larvae of some shallow-water inverte- pendix. brates can cross great oceanic widths (SCHELTE- General aspects of the biology and evolution MA & WILLIAMS1983; SCHELEMA1989, and lit- of hydroids and hydromedusae, with particular erature reviewed therein). But the distances are reference to remote-island forms, are considered still so great as probably to prevent the dispersive further elsewhere (CORNELIUS1992). planula andor hydromedusa stages of many hy- The specific aims of the present paper are to droids, from reaching the Azores, with consequent report additions to the known hydroid fauna col- implications for the fauna. Some hydromedusae lected during "Expedition Azores 1989" together can bud off new medusae thus bypassing a ben- with some previously collected specimens, to re- thic stage and this might substantially increase view and confirm existing records, and to assess the biogeographical implications of the species re- records missed by REES & WHITE (1966) are corded from the Azores. listed in Table 1. The first report of hydroids from the Azores THE LEPTOLID FAUNA was by LAMOUROUX(in FREYCINET1824), who recorded .'Tubularia clytoides' (discussion in CORNELIUS1982: 118- 1 19). Records and collections of leptolids from the Azores MEYEN(1834), who was wrongly cited by REEs &' WHITE(1966; details in CORNELIUS 1982: 50, 118-119), record@ and described two There are few publications treating the Azores hy- previously unknown species. The first, Silicularia droids (MARTINS1990). The majority of records of leptolids from the Azores region are of the hy- gracilis, based on infertile material, came from 'the Sargasso Sea, in the neighbowhood of the droid stage. Most the species recorded do not of Azores' and was presumably found on floating have a free medusa stage in their life cycles. This bias in the records might simply have been be- weed The species still defies accurate identifica- cause most of the visiting expeditions have con- tion (CORNELIUS1982: 50) but a related or identi- centrated on benthos, so that species which are cal species, S. bilabiata, has been redescribed re- predominantly medusoid might have been missed. cently by HARRIS(1990) from Australasian wa- But it seems the bias may validly reflect the com- ters: it has a medusa stage. The second, Senularia position of the fauna. indivisa may not have been evaluated by any re- cent reviewer of the group. Meyen stated it to be 'very similar to' the ubiquitous Dynumenu pumila A. Records before 1965 of more northerly waters. The stated substrate was 'mussels or marine plants'. This is noteworthy A nearly complete summary of records and auth- since mussels are rare in the Azores, only en- ors prior to 1965 was provided by REEs & WHITE countered sometimes on floating objects, such as (1966). Their survey need not be repeated except buoys (H.R. Martins, pers. commn.). Meyen's to mention that several major expeditions had figures show a sertulariid with exactly opposite, until that time provided virtually all the records. paired hydrothecae and S. indivisa might be Among the ships were the 'Josephine' (1860s), referred to one of several species possibly occur- 'Challenger' (1870s), 'Talisman' (1880s), and the ring in the area. However, the elongate nature of Prince of Monaco's 'Hirondelle' (1890s). Certain the hydrotheca and the long internode suggest that Table 1 Hydroid records from Terceira island additional to those of REES & Wm(1966) Species Locality Depth Date Material Comments

Sertularella gaudichaudi* Silveira harbour 5 19.vii.59 ? Mentioned by BAKER(1967: 40, as S. rnediterranea) Monte Brazil W 18-21 27.vii.59 ? Frodinhas interti- viii.59 ? Rocks dal to 27 S of Terceira viii.59 Epizoic On specimen of Haleciurn colony sessile recorded by REEs & WHITE (1966); mentioned Ijy Corns1975b: 406, foot- note, as Lafoenia sp.; only Azores record the nominal species should be referred to Triden- B. Records since 1965 tata distans Lamouroux (as redescribed in CORNE- LIUS 1979, as Sertularia). If this is accepted The hydroid and,medusarecords of BAKER(1967) MEYEN'S(1834) record becomes the earliest of T. seem to have been widely overlooked, and since distans from the Azores region. that publication is scarce they are summarized in In contrast the species Halecium nanum Table 2. BAKERprovided the first Azores, and ALDER1859, also collected from floating weed, also European, record, of Laomedea pseudodicho- has been widely accepted. The type material was toma. The species has since been collected from taken from its most usual substrate, Sargassum, a SW mainland Portugal (in 'plankton', estuary of few hundred km from the Azores at 34" 48' N, 34" R. Mira, May & October 1984, coll. J. Paula, det. 25' W (CORNELIUS& GARFATH1980; redescrip- S. J. Moore, BMNH regd no. 1985.3.5.7-8) but so tions of the species in CALDER1991 and Corn- far not further north. Other records of it are from LrUs in press). It evidently disperses widely across the coastal waters of Senegal, Ghana and Ivory the North Atlantic Ocean and has recently been Coast (CORNELIUS1982). noted thriving on Rockall in water hitherto con- A feature of BAKER'Srecords is the high pro- sidered prohibitively cool (CORNELIUSin press, portion of hydroid specimens collected from float- coll. K. Hiicock & al.). Thus the species will al- ing substrates (Table 2). BAKER(1967: 41) noted most certainly occur in the Archipelago and can that 'Clytia hemisphaerica can be replenished on be admitted to the faunal list in anticipation of its Sargassum'. This comment on rafting was poss- discovery. ibly stimulated by conversation with W.J. REES RITCHIE'S(1908) record of 'Clytia geniculata' who helped BAKERwith his identifications. REES previously stated to be from the Azores (CORNE- had made a similar 0b~e~ationwith respect to all LIUS 1982: 86) was in fact from the Cape Verde shallow-water Azorean hydroids (REEs & WHITE Islands. The species involved was almost certainly 1966: 281). RALPH (1961c), who had visited that known today as C. linearis of which there are REES, had earlier made similar remarks in relation a few genuine Azores records. to the New Zealand hydroid fauna, but HINCKS More recently, and after a substantial period (1868: 140) had recorded Clytia on floating Sar- during which apparently no leptolid collecting gassum earlier still. took place, there were expeditions from three col- Among the nine nominal species and sub- leges of London University: Queen Mary College species of hydromedusae recorded by BAKERfive [QMC]in 1952 (CHAPMAN1954, 1955), Imperial were oceanic, two were coastal and two further College [Ic] in 1959 (REES & WHITE1966), and coastal species were taxonomically dubious. Of Chelsea College [cc] in 1965 (BAKER1967). The the coastal taxa the rafting of Clytia hemisphaeri- cnidarian collections from the IC and cc expedi- ca has just been mentioned, and Zanclea costata s. tions were described by these authors and are dis- str. was stated by BAKERto be endemic to the Me- cussed.below. The material from the Ic expedition diterranean and thought to have been brought to (mostly hydroids plus a few scyphomedusae and the Azores with Mediterranean Water. anthozoans, there being no hydromedusae) has VANSOEST (1973) gave a list of oceanic hy- BMNH registered numbers of the series dromedusae from the mid-Atlantic Ocean. From 1962.1.15.1-32, 1962.2.10.1-38 and 1962.2.13.1- the Azores area he recorded Calycopsis typa, the 8, and that from the cc expedition 1986.1.2.1-22 narcomedusan Cuninu duplicata, Pandea-conica, (scyphomedusae and siphonophores) and and, Sibogita geometrica, the first three not hav- 1986.1.3.1-20 (hydroids and hydromedusae). I ing been reported from the area before. have not located cnidarian material from the QMc There has been a long-running Dutch project expedition. to study biological aspects of the Macaronesian is- KRAMP(1959, 1961) provided an indication of lands which has taken in the Azores, 'the CANCAP which hydromedusae might be expected in the Project (Contributions to the Zoology, Botany and North Atlantic Ocean and hence which open- Paleontology of the c~~arian-CARVerdean Re- ocean pelagic species might occur in the Azores. gion of the North Atlantic Ocean; DEN HARTOG 1984), organized by the Rijksmuseum van Na- tuurlijke Historie [RMNH], Leiden. Large collec- Another Dutch expedition studied plankton, tions were made but those of hydroids, preserved including hydromedusae (WINKLER1982). Win- in the RMNH,have yet to be studied. kler recorded 30 species of hydromedusae, many from the general area of the Azores, and provided

Table 2 The Azores hydroid and hydromedusa records of BAKER (1967) excepting those of Sertularella gaudichaudi sens. CORNELNS (1979), which are given in Table 1. All were stated to have been collected from 'the coast', and those below were from Sao Jorge island. Species Locality Depth Date Material Comments (m) i) Hydroids Clyria hemisphaerica Santo Cristo 'surface' 10.viii.65 'Small colonies' One on drift wood, several on Urzelina 0-2 2.ix.65 " Grareloupiafilicina, one each on Codium adherens and Polys~phontasp. Orthopyxis integra Urzelina Recorded as 0.caliculata; all on G. licinia; earliest Azores remr di Laomedea Urzelina 'surface' 3.ix.65 Large colony On floating polythene; see text pseudodichoroma 'up to' 4cm high; fertlle male and female Sertularella Santo Cristo 'surface' 10.viii.65 One unbran- Recorded as S. mediterranea; audichaudi sensu ched colony on floating brown alga 8oms 1979 Sertularella polyzonias Urzelina 1-10 30.vii.65 Mostly On Pinna rudis, sponges, and unbranched G.filicinia colonies Tridentata distans Santo Cristo 'surface' 9.vii.65 Many small Recorded as S. distans var. colonies gmcilis, on floating brown algae Aglaophenia plurna Urzelina 0-3 2.ix.65 Small colonies On G.filicinia ii) Hydromedusae Clytia hemisphaerica Off Urzelina 0-120 ' 1965' . ? 'Clytia bnmescens' 11 'A few spe- 'Fist' for the Azores of this cimens' unassessed nominal species Krampella dubia First ever Oceanic species; this specimen complete apparently never descnbed specmen Sromoroca rugosum First Azores record Zanclea costata s. str. One spe- First record of nominal species cunen outside Mediterranean Sea; thought b BAKER (1967) to bc eviJnce of transport by Mediterranean Water Aglaura hemistoma Many Oceanic species specimens Rhopalonema velarum ? 11 Solmaris corona Lyriope tetraphylla ? a zoogeographical analysis related to water-mass 58 full species currently regarded valid. Precise origin. Later cruises of the same expedition pro- counting is not possible since some of the tam are vided more than 60 species from the same region of uncertain status. including two new to science, and a detailed fau- Some thirteen species of hydroids have since nal analysis was made (BLEEKER& VAN DER been added to the faunal list and a number of hy- SPOEL1988). Though these accounts greatly in- dromedusae (Table 3 and elsewhere in this paper). creased the local faunal list most of the species Most were collected by the present expedition, were known to be typical oceanic forms. Probably two were recorded by BAKER (1967), one none was g shallow water coastal species, perhaps (Laomedea calceolifera) was collected by Dr a reflectiop of the sampling stations most of which Helen Martins in 1980 and is newly reported here, were, in fact, in open-oceanic waters. and there is a single record of Lafoeina tenuis ,(Table 1; CORNELIUS1975b). The last-named C. Hydroids identified during the 1989 joint species was from 610 m and Laomedea calceolife- expedition ra from ca. 100 m, but the other eleven newly re- corded hydroids were mostly taken within a depth Material came mainly from two sources. First, range of 0-30 m. This reflects the emphasis of ear- from snorkelling and from the expedition's SCUBA lier collecting effort on the group, which before divers who worked to a depth of c. 30 m. Second, the 1950s was exclusively deeper than 100 m. from a collection of a few dozen specimens col- Several of the species newly recorded in the lected .previously, mainly by dredging, by Dr Azores came from sheltered pontoons in the now Helen Martins, DOPH. In addition a little informa- busy Horta yachting marina, a locality probably tion was provided by a remote underwater video subject to recruitment from ship-borne colonies. camera operated by Dr Richard Nash, Port Erin Most of this habitat has been created since REES Marine Laboratory [PEML],University of Liver- & WHITE(1966) wrote. The four species Silhouet- pool, at depths down to ca. 100 m, during the ex- ta uvacarpa, Tubularia crocea, T. indivisa and pedition. The records were all from Faial and are Ventromma halecioides were found only at this grouped in Table 3. place. The last three have been widely recorded as Hydroids were also sought, unsuccessfully, on fouling organisms on marine structures (MORRI& the north coast of Sb Jorge island in a coastal la- BOERO1986) supporting the view that ship trans- goon at Caldeira do Santo Cristo; on Faial island port could have occurred. The first species is dis- in an intertidal natural sea-water swimming pool cussed in more detail below (p. 88). at Varadouro, in the often moderately sheltered Several 'second records' from the Azores were bay west of Porto Pim, and in the rock pools on collected by the present expedition (Table 3) and the exposed rocky shore at Feteira; and on Pico is- are as informative as the 'first records': Pennaria land around the moderately sheltered coastal disticha (30 m), Sarsia tubulosa (0.5 m), Hale- rocks and gullies to the south of Madalena, and in cium tenellum (30 m), Clytia linearis (10-12 m), the extensive shallow lagoon at Lajes do Pico. Obelia bidentata (?ca. 3 m), Orthopyxis integra The virtual absence of hydroids from these places, (0.3 m), and Kirchenpaueria similis (2 m). Strict- all except Feteira being topographically suitable ly, the record of Obelia bidentata is the third, the for their growth, emphasizes their scarcity in the species having been recorded by RED & WHITE region. (1966) as 0. bicuspidata (Table 4). These several species are virtually cosmopolitan in coastal wa- FAUNAL ANALYSIS ters within their normal latitudinal ranges. None of these 'second record' species was taken in the sheltered waters of the Horta marina RED & WHITE(1966) listed some 66 nominal They thus tend to ccmfinn that rhere is a 'true' hy- species of hydroid recorded from the Azores. Tax- onomic revision has removed about 9 of these, droid fauna in the Azores Archipelago and that and 5 varieties they listed are not recognized by the earlier records of these species need not be considered unusual. They may not have been all authorities (Table 4). Their list includes about ship-borne. Table 3 Some new records of hydroids from the Azores, including some of species not recorded from the area before.

Species Locality Depth Date Material Habitat and other notes (m)

TUBULARIUDAE ***Tubulana Horta marina 0.3 25.vii.89 Several fertile On tubes of.po1ychaet.e crocea colonies-DOPHI Sprro ra has s allanranii and BMNH; doll. on pofydene Koats m shade PFSC ***Tubulana Horta marina 0.3 26.vii.89 Several infertile On moored polythene float indivisa colomes; BMNH; coll. PFSC HALOCORDYLIDAE * *Pennuria SE corner of Fullv exwsed coastline: ~revious disticha Monte da Guia k&es &cord Terceira ( ~ E& S WHITE 1966 as Halocord le tiarella: disdussion in C#~%ONS & RY- 1989); this sample and next had unusual1 long ramules (cf. CALDER 1688) Ilh6u Nemro entre 22.vii.89 2 colonies, up to See previous Montes, aorta ca. 8 cm; infertile; coll. J. Azevedo CORYNIDAE **Sarsia sp. cf. W coast of Monte 1 .viii.89 Small,fertile Fully exposed caastline; see text tubltlosa da Guia colony with near-release medusae. BMNH. boll. R. & A.-M. Patzner EUDENDRIIDAE ***Eudendrium sp. eamount 3km 20 vii.89 Some fertile; ~SEof Horta DOPWBMNH SE corner of 10 vii.89 Small colonies; Fully exposed coastlime; same Monte da DOPWBMNH specles as above Guia; 20 m inside cave NE comer of. vii.89 DOPWBMNH Slightly less exposed; same Monte da Gma specles as above BOUGAINVILLIIDAE ***Bougainvillia sp. Horta marina 0.3 26.vii.89 Infertile colo- On ro e and lythene float; nies; BMNH; very s!eltereF' coll. PFSC Horta harbour 2 vii.89 as above On S. spallawanii on jetty; sheltered SE corner of 25-30 vii.89 as above Fully ex osed coastline; Monte da all rec.or8s of one well- Guia in cave estabhshed specles ***Silhouena Horta marina 0.3 2.vii.89 Sevqal thriving On live and dead uvaearpa onwards colorqes, some Mytilus edulis releasmg medusae; BMMI; coll. PFSC HALECIIDAE **Haleciwn 30 28.vii.89 Two infertile Previous Azores record by tenellurn colonies on PICXXT & BEDOT (1900. clted SertulareUa in REES & Wm1966) DOPH- coll. k. & A.-M.'~atzner *denotes the first and ** the second Azores record of the species, and *** the first of the genus. First records from individual islands are not noted. The localities are around Faial island unless otherwise stated. Most of the material came from the ecological collections of the Expedition (see Introduction) and, where Table 3 (cont.) Species Locality Depth Date Material Habitat and other notes (m). , LAFOEIDAE Cryptolan'apectinata near Horta ca. 30 vii.89 One colony; coll. On base of hydroid D. Moss Polyplumariaflabellara CAMPANULARIIDAE Clyria Monte da Guia, 3 17.vii.89 5 unithecate pedi- On tunicate cf. S eUa hemisphaerica on.SW coast of cels on stolon- several previous f#zor&s of lnner crater infertile; B~Hrecords . **Clytia linean's Seamunt 3 10-12 31.vii.89 Several dense co- On Dictyota dichotoma. km ESE of lonies, some relea- two evlous records Tkrceira Horta sin medusae- (&& WHITE 1966) DO%H;all. Ik~ate Off Castelo ca. 100 1.x.80 About 20 fertile Distinctive female Bran00 male, female and gonothecae present infertile shoots up to 2.5cm. DOPI%- coll. ~.&.~artifis Obelia bidentata Ilhku Negro ? 22.vu.89 One infertile colony, entre Montes; ca. 4cm with lon Horta hydroth&cae;DO&; coll. J. Azevedo **Orthopyxis W coast of 0.3 l.viii.89 Small fertile On Balanqs tinrinnabulum;yery integra Monte da Guia; colony with fully exposed situation; one revlous developed 'intra- Azores record (Table 8 capsular sporosacs' , onads brown- fiw; coll. R: & A.-M. Patzner SERTULARIIDAE ***Amphisberia At entrance to 15 18.vii.89 Dense clum Open coast; some Eudendrium operculata cave off SE ca. 5cm hi 9- in sample comer of Monte infertile; D~P~I; da Guia coll. D. Moss *Diphaski cf. On seamount 20 17.vii.89 Two small infertile On Sertularella and fucoid; altenuata 3km ESE of shoots one with poor.materia1, identifkation Horta tendril; BMNH provisional **Dynqmgna On seamount 10-12, 17,31.vii. 3.samples; colo- Common at this location comzczna 3 km ESE 20-56 89 mesu to6cm of Horta infede; D ~d BMNH. col? C. R. ~ood,'~.Bate Sertularella 5-20, vii-viii.89 Many colonies, Ubi uitous; endin to be in audichaudi sens. 20-56, some fde. co&e turf m sh8lower 6Oms 1979 down DOPHJBMN~ localities and in more open to ca. microniches deeper; eplzoic 100 iin laces; reviously :&%aas ,! medz Brranea Sertularella gayi off Espala- ca. 100 5.iv.79 5 infertile innate Both this and S. 01 ~onias maca colo 'es ~OPW have been recorceed%efore; coll.%.k ~artihs distinctions are roblematic (CORNELIUS 19%) On seamount ca. 20 17.vii.89 3 infertile stems See above 3 km ESE of up to 6cm. DOPH; Horta coll. C.R. kood Tridentata distans SE corner ca. 15 18,28.vii. Several infertile At entrance to cave at 15 & of Monte ca 30' 89 unbranched shoots 30 m; on open coasthne; da Guia

PLUMULARIIDAE HALOPTERIINAE Antennella 1 mile off 100 5.iv.89 Several infertile On A lao henia acacia secundaria Espalamaca colonies + loose over %ivdve reef REES & fra ents- DOPH; (1966 ci& 5 C0fi.~.hns PreVIOUS recOrL98-1250 rn Table 3 (cont.)

Species Locality Depth Date Material Habitat and other notes (m)

**Kirchenpaueria Outer side of old 2 26.vii.89 Two infertile On tubes of polyc aete srmrl~s in SW corner plumes; BMNH; S irogra his spal!anzanii coll. PFSC sielteregrecorded from 5er- ceira by &ES & Wm1966, as K purnata var. sirnilis\ PLUMULARIINAE Nemertesia ramosa Off Castelo ca. 100 1.x.80 One 12cm colony; Branco DOPIj; coll. H.R. Marhns SE corner of 30 28.vii.89 Two 7.5cm colonies, Monte da Guia at entrance to rift

Off Espala- ca.100 29.vii.89 Many colonies seen maca by remote TV.via R. Nash; det. PFSC Plumularia setacea Off Castelo ca. 100 1.x.80 DOPH; coll. H.R. Four evious Azores records, Branco Marhns two oyvar. elongata edot (ms& wm1968 SE corner of 5-10 vii.89 Several lumes Monte da Guia, some w$h distihc- at entrance tive onothecae; to cave DOP~MNH; coll. D. Moss * ** Ventromma Hortamarina 0.3-2 18.25.vii Abundant: On s nge S. halecioides 89 infertde. DOPH; spal&zanh & coll. PFSC polythene float AGLAOPHENIIDAE Aglaophenia acacia 1 mile off ca. 100 5.iv.79 8 trichotomously- Fr uent from 15m Es alamaca, forked colonies; (2s& W- on%ivalve reef DOPH- coll. 966) probably to H.R. &lartins hundreds of metres Same area 27.vii.89 Numerous colonies seen b remote TV; via R, hash; det. PFSC Qff Ribeiras, 120-180 5.ii.89 Two infertile On Charonia lamgas shell Pico lumes u to occupied by pagund 8 cm on gort stolon DOPH; coll. H.R. h;lartins 'Azores' Det. A. Svoboda No further information; (pers. commn) records and material lost; recorded from Canaries by SVOBODA & CORNELIUS (1991) Aglaophenia pluma From variet of vii.89 Numerous colo- Common where indicated; on exposed anJshel- nies up to 8 cm varied substra@s including tered situahons. on some stones rock, P~nmshell, . inside and outside iede- DOPW fuco~dk;.psnble~xonormc Monte da Guia; BMNI~.coll. un hcabons of vaned also on seamount 5-20 D. MO~,C.R. sugstrata discussed in 3 km ESE of Wood, and SVOBODA& Horta others Corns(1991) A lao henia Off Castelo ca. 100 1.x.80 DOPH coll. Epizoic on Nemertesia tu%u&ra Branco H.R. &fartins ramosa On seamount Infertile colonies 3kmESE Horta; 20 17.vii.89 u to 7cm- DOPW B~H;C.R. Wood Table 4 Changes in taxonomy and interpretation of some earlier records since the lists of REES & WHITE (1966). Species are listed in alphabetical order as in that paper.

1. Aglaophenia pluma. As in many hydroid s ecies no varieties are now recognised, the extremes of variation once given such status now being regardeBas phenotypes (SVOBODA & CORNELIUS 1991). 2. Clytia gigantea is now referred to C. hemisphaerica (see CORNELIUS 1982). 3. Clytia longicyatha has been referred to Obelia bidentata (see CORNELIUS 1975a: 264) but a review of its va- lidity would seem necessary. 4. Clytia nolifomis sens. REES & WHITE is flobably best referred to C. hemisphaerica (discussion in CORNELIUS 1982: 80). The main character on which it was based, the stage of medusa development on re- lease, varies in Clytia (noted in HINCKS, 1868: 147; summary in CORNELIUS 1990a: 545). 5. Clytia raridentata. Several authors, including REES & THURSFIELD (1965), have referred this nominal species to C. hemisphaerica and recent studies of its type matma1 have upheld thls mew (CORNELIUS & GARFATH 1980; CORNELIUS & OSTMAN 1986). 6. Clytia striata. Should probably be referred to C. linearis (discussion in CORNELIUS 1982: 86). 7. Halocord le tiarella has been widely regarded as cons cific with Pennaria distichs, the generic and specific names orwhich must each take priority (GIBBONS &&LAND 1989). 8. Kirchenpaueria pinnata var. similis is here considered a full species, following HINCKS (1868) among others. The nominate 'variety' has not yet been recorded from the Azores. 9. Lafoea fntticosa is referred to L. dumosa (discussion in CORNELIUS 1975b; VERVOORT in REES & VER- VOORT 1987: 44). 10. Lafoea serrata is referred to the genus Filellum (following MILLARD 1975). 11. Obelia bicuspidata is called 0.bidentata (discussion in CORNELIUS 1975a). 12. Obelia hyalina is of uncertain taxonomic status but was robably based on 0.dichoroma which is otherwise recorded from the Azores (discussion in CORNELIUS 19%~:99,119). 13. Obelia kincaidi sens. Rees & White has been provisionally referred to Clytia (by CORNELIUS 1975a: 280) and the Azores record itself has been challenged (CORNELIUS 1982: 90). Although CALDER (1971,1991) provisionally recognized the species full evaluation is desirable. 14. Orthopyxis clytioides sens. Rees & White has been reidentified as Obelia s . (by CORNELIUS 1982: 118-119) and was almost certainly based on one or other species of that genus akea& recorded from the Azores. 15. Sertularella ha(Allman) sens. Rees & White is ovisionally referred to S. gaud!chaudi sens. CORNELIUS 1919. The similarly-named deepwater Thuiaria & (Allman) is a different normnal speclea and IS probably vahd (CORNELIUS 1979). 16. Sertularella mediterranea is provisionally referred to S. gaudichaudi sens. CORNELIUS 1979. 17. Sertularia distans var. gracilis was never soundly based and is no longer reco nised (CORNELIUS 1979). Discussion on referral of the species to Tridentata has been given most recenty by CALDER (1991). 18. Thecocalpus myriophyllum is referred to another genus, as Lytocalpia myriophyllum (discussion in REES & VERVOORT 1987: 177).

No analysis is attempted of the few but varied Remarkably, all but 3 of the 58 or so valid hydromedusan records for two reasons. Fist, the species listed by RBES & WHITE (1966) are present expedition did not collect plankton; and referred to the thecate suborder. In contrast, in the second, as BAKER(1967) and VAN SOEST(1973) group as a whole there are roughly equal numbers implied, the majority of hydromedusae occurring of athecate and thecate genera - about 170 of each in the Azores are probably deep- to mid-water (data extracted from BOUILLON1985). Of the 13 oceanic forms whose dispersal and distribution are species since added to the faunal list 5 are athe- governed by factors different from those affecting cate and 8 thecate, but the overall disproportion the mainly coastal-benthic species discussed here. remains between the Azorean records of the two suborders. It may not necessarily be due to the- ing ocean currents. In addition the rather uniform cates being the commoner. The typically greater subtidal and intertidal environments probably re- colony size of thecates may have led to their more strict the variety of species. Descriptions of frequent detection and collection. However, pres- Azorean shores and their biota have been pro- ent records are probably a true indication that they vided by MORTON(1990) and HAWKINS& al. are the more numerous of the two groups in the (1990). Around the coasts of Faial and Pico, for Archipelago. example, there are no eelgrass beds, no shores In the Hydroida as a whole, about 55% of the covered by large brown algae with the exception genera have species releasing a fully developed of a Cystoceira zone in some places, and no coral hydromedusa. The remainder have the medusa reefs or mangrove areas which might provide per- stage reduced, in most being completely sup- manent habitats for many species. The diversity of pressed from the life cycle. In the known Azores habitats is much less than on comparable con- leptolid fauna the proportions are remarkably tinental coasts less exposed to extreme wave ac- lower (40%). This holds true for species both tion. Some of these factors will now be considered deeper and shallower than 90 m (Table 5). The further. disproportion between the two life-cycle groups is discussed below (p. 89). A. Physical and geographical factors

DISCUSSION i) Remoteness, and depth of surrounding abyssal plain. The Azores are a long way from both the Euro- THE NATURE AND DISTRIBUTION OF THE HYDROID African coast and the Americas. The least dis- FAUNA, AND THE FACTORS AFFECTING IT tance from the islands to land is about 1300 h,to the region of the Strait of Gibraltar. The Archipe- Several major factors seem to influence hydroid lago is about the same distance from the nearest distribution in the Azores region: the relatively Shelf on the American side, the Newfoundland young age of the islands and associated sea- Ridge, which extends to approximately 39" N, 45" mounts, the great depth and breadth of the sur- W. The nearest extensive coastal waters on the rounding abyssal plain, the heavy swell the islands western side are the Grand Banks off Newfound- experience, and the areas of origin of the prevail- land and the NE coast of South America, each ap- proximately 3000 km distant. The islands are thus

Table 5

Numbers of benthic hydroid and medusa species recorded from the Azores region to show proportion releasing a fully functional hydromedusa.

Below 90m (100m) Above 90m (100m) Totals % Totals %

Species releasing fully functional medusa 3 (3) 6 (7) 5 (4) 15 (10) Species having ephemeral or no medusa stage 45 (41) 94 (93) 28 (36) 85 (90)

Compare the percentages, shown in italics. Medusa-releasing species are little recorded at any depth. An arbitrary depth of 90m separates coastal forms from deeper-water ones. The effect of a single, species-rich expedition trawl at a nominal 98m is shown by including (in parentheses) corresponding species-totals above and below 100m. Species recorded both above and below 90m (and 100m) are scored twice. Data from nearly all sources discussed in the present paper are pooled. The hydromedusan records of BAKER (1967) are not included since the depth of collection of all samples was given as 0-120m (present Table 2). Four nominal species of Zygophylax recorded by REES & WHITE (1966) are assumed taxonomically valid. Deep-sea and open-ocean hydromedusae each form a distinct faunal assemblage and are not included. See also Table 6. the most remote in the North Atlantic. The main itially westwards, and North Atlantic Deep Water biogeographic questions to be answered are: (NADW;below 2000 m) arriving from the north which shallow-water species might be able to (HELLAND-HANSEN& NANSEN 1926; PIO& cross the intervening abyssal plain from the near- EMERY1982; BIGG1990; clear summary and fur- est populations likely to provide recruitment to the ther literature in GOFAS1990). Labrador water has islands, whence might they come, and how might also been reported off the north-western region of they travel? the Azores mainly at depth between the NACW and NADW (HARVEY& ARCHAN 1988). ii) Young age of the Archipelago. The oldest recorded The MW was shown by HELLAND-HANSEN& Azorean rocks date from about 8 my BP (ABDEL- NANSEN(1926: 44) to sink down over the Por- MONEM& al. 1975) and 5.5 my BP (FERAUD& tuguese region of the Continental Slope. It event- al. 1984). The age of the associated sub-surface ually reaches the Azores and the region to the seamounts is arguably more relevant to Azorean south at a depth variously reported over the range marine biota than the age of the terrestrial compo- 600-1800 m (BIGG 1990; synopsis in GOFAS nents of the Archipelago, but 5-8 million years is 1990), the range probably reflecting the varying itself sufficiently long a period for much faunal depth of its fluctuating wedge-like intrusion. HEL recruitment to have occurred. Although marine LAND-HANSEN& NANSEN(1926) recognized an faunal endemism is not a widely reported feature anti-clockwise sub-surface gyre between Portugal of the Archipelago (BRIGGS1966,1974) there has and the Azores region of the Mid-Atlantic Ridge, perhaps been adequate time for a natural faunal and a reverse one immediately to the north (their assemblage to accumulate and stabilise. Fig. 15). BIGG (1990) regarded variation from the normal current directions in the region as com- iii) Ocean currents. The surface-water Gulf Stream monplace. Such gym and current variations (GS) passes northwards off FIorida, Georgia and would facilitate dispersal from southern Europe South and North Carolina. About the latitude of and the Mediterranean Sea at a range of depths New England it turns ENE and then E. From here from perhaps 100 m to 1500 m. it is known as the North Atlantic Drift or, in mod- em literature, North Atlantic Current (NAC).Part iv) Sea temperature. Some tropical species which continues on towards northem Europe but a large might be carried from the Caribbean sea to the part turns towards south-eastern Europe and North Azores on flotsam would not survive in the cooler Africa and is termed the Azores Current (AC). waters of the mid-Atlantic. The sea surface tem- Accounts of the surface currents relevant to the re- perature around the Azores ranges from ca 23" C gion are available in the publications cited above. in August down to ca. 15" C in February (NAVAL HELLAND-HANSEN& NANSEN (1926: 30) were INTELLIGENCEDIVISION 1945) or even 14" C among the first to study the southward-flowing (H.R. Martins, pers. cornmn). Thus many of the AC.In their view it left the NAC at ca. 46-49" N leptolid species recorded from Bermuda (CALDER and this has been repeated by some later authors. 1988, 1991) may be unable to survive in Azorean The AC is unstable and produces temporary ed- waters. However, a range of species more tolerant dies and meanders which are responsible for the of cooler conditions, originating from slightly fur- large variation generally observed on the superfi- ther north on the eastern U.S. seaboard as the Gulf cial current- field (ALVES1991). The surface layer Stream passes northward, might nevertheless be (0-600 m) is mainly of local-origin North Atlantic expected as with marine algae. Unfortunately, Central Water (NACW).However, even when the though many of the recorded hydroids fall into GS arrives here (as the Azores Current) the water this category many of the species exist also on Eu- is already transformed (HARVEY& ARCW ropean coasts so that an American origin cannot 1988). be demonstrated. Bottom- and mid-water arriving at the Azores is more varied in origin, comprising three main V) Ocean swell and tidal amplitude. CHAPMAN(1954) components: Mediterranean Water (m;depth of provided a summary of the greatly exposed inter- 600-2000 m) leaving the Strait of Gibraltar in- tidal conditions prevailing in the Archipelago. Even on windless days powerful waves of distant in the tropical East Atlantic where fish have been origin and long period crash on virtually all identified as a major source of grazing and control shores, refracting around promontories and into of small algae (review in JOHN& al. 1992). bays with much of their energy retained. On some Young hydroids and other small benthic organ- days during most winters the wave force becomes isms might also be browsed or disturbed by fish, extreme and potentially equal to that anywhere in either as a mechanical consequence of the grazing the world. The majority of Azorean shores are or by spcific predation. Very Exposed to Extremely Exposed as defined by British standards (e.g. BALLANTINE1961; ii) Distribution and depth. halysis of the distribu- LEWIS1964). In such environments most hydroids tion of the recorded hydroid fauna in relation to incur mechanical damage and do not survive. The depth is greatly assisted by REES & WHITE'S prevailing wind directions throughout the year are (1966) synopsis. about equally from NE and SW (~ALINTEL- Valid depth-band groupings are difficult to LIGENCE DIVISION1945; CHAPMAN1954), SO that determine. REES & WHITE pointed out that the there are few permanently lee shores. question is complicated both by the poorly do- The shallow tidal amplitude of the region, less cumented tendency of some (but not all!) boreal than 2 m at springs and a tenth of this at neaps shallow-water species to 'descend' to greater (CHAPMAN1955), narrows the intertidal zone. But depths with decreasing latitude, seemingly surviv- the nearly incessant, heavy swell usually extends ing best within certain temperature ranges; and by the vertical range of the intertidal biota consider- limitations in our knowledge of the shallow-water ably beyond these tidal limits (HAWKINS& al. fauna. Some hydroids undoubtedly have narrower 1990). depth ranges than others, even within coastal wa- Two subtidal hydroid species have been found ters (CORNELIUS1979: Fig. 2). In addition, forms to be successful in these harsh conditions. The characteristic of the upper 30 m alone have strong coastal medusa-releasing hydroid Sarsia tubulosa swell and browsing fish to contend with (see was reported by CHAPMAN(1955) in the protec- above) and this may further influence the ob- tive coralline turf off Terceira $t a density of 900 served pattern. hydranths (not colonies) per m . The present ex- Thus the high proportion of species recorded pedition recorded the species only once, off Faial, deeper than 90 m is the reverse of the better-stu- but there found Sertularella gaudichaudi sens. died situation-in most boreal seas where the shal- CORNELIUS(1979), commonly in the coralline turf low fauna is the richer. The difference may partly (Table 3). reflect sampling effort and techniques used, a sub- At least down to 20-30 m depth in coastal situ- stantial portion of previous work having sampled ations the expedition's divers noted the hydroid depths below 100 m by dredging from sizable re- fauna to be otherwise sparse. But on the seamount search vessels. In fact 17 species, roughly a quar- 3 km,ESE of Horta at about the same depth a richer ter, have been recorded in the Azores only in wa- hydroid fauna was found including several species ters shallower than 30 m, and 37, about half, only with tall colonies (Table 3). Thus the wave-force deeper than 90 m (Table 5). There are 5 from 201- factor limiting hydroid survival may be the crash- 300 m; 3 from 301-400 m; none from 401-500 m; ing of the swell, probably during winter storms, two from 601-700 m; none from 701-800 m; 4 rather than wave surge which would be experi- from 801-900 m; none from 901-1100 m; and per- enced on the seamount and subtidally along coas- haps an abyssal contingent of 6 species so far re- tlines alike. corded in the area only from 1160 m and deeper (data mainly from REEs & WHITE 1966). The B. Biological aspects figures are biased by chance bunching of existing records from certain fortuitously species-rich ex- i) Browsing by sabtidal fish. Browsing fish are pedition dredge-hauls at nominal depths of 208 m, numerous subtidally in the Azores in all but the 599 m, and 610 m - each close to a multiple of most exposed regions. This is typical of coastlines 100 m. iii) Medusa suppression among Azorean hydroids. The The eighth species, the medusa-releasing Sar- low proportion of medusa-releasing leptolid sia tubulosa, is not known to raft, However, its species recorded at all depths in the Azores is known micro-habitat in the Azores, amongst tight- striking. The figures in Table 5 represent about ly-packed coralline algal fronds (CHAPMAN1955), eight species, all of which are known or probable suggests that it may be able to survive a long jour- rafters which, therefore, may have au-ived in the ney amongst the epibiota on a well fouled ship's Azores by means other than the dispersive capa- hull or natural floating substrate. Since it may not bility of their medusae. Their likely mode of yet have been recorded on ships, rafting on weed travel therefore, seems to be rafting of the hydroid seems the more likely (W. Vervoort, pers. stage. commn). Six of the eight are ubiquitous, coastal-cosmo- Lastly, and additionally, the species Silicularia politan Campanulariidae of just two genera (Cly- gracilis was described from the Sargasso Sea and tia hemisphaerica, C. linearis, Obelia bidentata, the Azores by MEYEN(1834) whose material was 0. dchotoma, 0. geniculata, 0. longissima). The infertile. The.related and perhaps identical nomi- hydroid of C. hemisphaerica has been recorded on nal species S. bilabiata has a short-lived medusa a variety of planktonic substrates including pe- stage which could not cross the Atlantic Ocean. If lagic cirripedes and crustacean ectoparasites of S. gracilis resembles this and several other ortho- fish (review in CORNELIUS1982; further example, pyxine species in having a reduced medusa (surn- on floating material far from land, in VERVOORTmaries in MILLARD1975, CORNELIUS1982) it too 1985). C. linearis also habitually rafts on oceanic may well have rafted to the Azores on weed. pteropods and so pursues both benthic and 'neritic' life-styles, making it one of the most iv) Dispersal methods in remote island marine fame. widely distributed of marine invertebrates (COR- The paucity of medusa-releasing species in the NELIUS 1982, 1987). The Obelia species, and Azores (Table 5) supports the hypothesis of others in rhe family Campanulariidae, have often RALPH(1961~) and KRAMP (1968) that coastal been recorded rafting (review in CORNELIUS hydromedusae cannot span great oceanic distan- 1982; further example in VADER& al. 1981, 0. ces - excepting the few medusa species capable of longissima attached to a pelagic isopod). All six reproduction by vegetative fission. Two further can disperse long distances by rafting, despite factors will certainly hamper transoceanic trans- their having well developed medusa stages (the port of medusae. First, that medusae of both medusa of C. linearis having been recorded for sexes, perhaps requiring two hydroid colonies, are the first time recently by BOERO& SARA1987). required for the life cycle to be completed The seventh, Silhouetta uvacarpa, has been re- (CORNELIUS1981; JACKSON1986). Second, that corded from the Azores just once, in Horta yach- liberated medusae will drift far from their coastal ting marina (Table 3), and is so little known sources before releasing planulae, which will then world-wide that zoogeographic comment is inap- have a reduced chance to settle close to newly es- propriate save that almost all its recorded occur- tablished colonies. Hence colonies of medusa-re- rences have been in harbours and similar places leasing species that do settle in remote places will (literature reviewed by CALDER1988). The close- probably be less successful in sexual reproduction ly related and similarly poorly known Clavopsella than species lacking a medusa stage. navis (literature review in MILLARD1975) differs Some recruitment of the few coastal hydrome- in having the medusa generation reduced to a spo- dusan species recorded in the Azores may result rosac and, though otherwise similar, would seem from medusae, qdthe planulae they give rise to, unlikely to be conspecific. Localities of C. navis being released in mid-Atlantic from already-raft- not known to Millard include the Netherlands (W. ing hydroid colonies. Such en route release of dis- Vervoort, pen. comm.) and Shoreham harbour, persive stages has been suggested to occur often southern England (PFSC & C. Sartory, unpubl.; among rafted animals (JACKSON 1986: 593). But details recently published by SHEADER& wide dispersion of the released stages must be so SHEADER1990). great as to make any resulting recruitment infre- quent. In invertebrates generally, and in hydroids too, settle rapidly from the plankton and hence sustain species with non-dispersive intermediate stages coastal populations. It has recently been sug- will have a much better chance of settling locally gested, however, that species having a suppressed and of contributing to a local population than will medusa stage also have short planula longevities those with long-lived planktonic stages. Such (SOMMERin press), but data are few. forms predominate in the faunae of remote is- A tendency towards philopatry has been re- lands. An extreme tendency of this kind, and in- ported in several invertebrate groups ancestrally cidentally one of the first examples recorded, was having a long-dispersing stage (JACKSON1986; noted by CRISP(1956) and F~SHER(1956: 167) on HUGHES1989). But this is$= from demonstrated the biogeographically isolated Rockall. FISHER among hydroids. The dispersive stages of the ma- (1956) made the first serious invertebrate collec- jority, whether planulae or medusae, probably re- tion from this islet. All of the half dozen 'interti- main planktonic long enough that settlement near dal' invertebrates recorded were either viviparous the parent colony does not occur (CORNELIUS or lacked a pelagic dispersive stage. The faunal 1990b, 1991). Settlement near the parent is known list was increased to about 17 marine invertebrates in very few species (CORNELIUS1990b). Appar- by MOORE (1977) but still none had a planktonic ently, too, close philopatry is rare in the group, for larva (see also JOHANNESSON1988). Other early few hydroids grow in clumps of colonies. discussions of the tendency towards limited dis- persal by island faunae were cited by SCHELTEMA C. Zoogeographic origin, currents and rafting & WILLIAMS(1983), HIGHSMITH (1985) and JOHANNE~SON(1988). Mytilus spp. are evidently i) Zoogeographic origin and currents. Some zoogeo- frequently transported to the Azores on ships but, graphic analyses have demonstrated an Azorean though individuals survive, permanent popula- shallow-water faunal element derived from the tions have not become established: perhaps on ac- Afro-European shelf and others from the North count of the planktonic larval stage of this genus. American region, and these will be mentioned The same reduction of the dispersive stage below. But hardly any of the leptolid species so seems to be a feature of the leptolid faunae of cer- far recorded in the Azores are endemic to one side tain oceanic archipelagos where documentation is of the Atlantic or the other. Hence it is useful to sufficiently detailed for sensible comparison summarize something of what is known of the (Table 6). Present knowledge, although fragmen- provenance of the other groups. However, it has to tary, suggests overwhelmingly that fewer remote- be said that most studies of the kind have simply island hydroids release medusae than do so in compared the faunae or florae of the Azores with continental-coastal faunae. those of other regions without considering by what means of transport each species might have V) Medusa reduction, perennation, and philopatry. The arrived. process of medusa reduction is most marked in Mediterranean Water is evidently important in species having large, perennating colonies (Table faunal recruitment to the Azores and surrounding 7). This may affect the faunal arguments region, despite its relatively small volume and the presented here since, in the Azores as elsewhere, fanning out that it must undergo. Certain sponges it is of course the larger and more conspicuous and the Mediterranean locust lobster, Scyllarides colonies which past collecting methods have most latus, are thought to have arrived with this current easily located. Some medusa-releasing species (BOURY-ESNAULT& LOPES 1985; MARTINS having small hydroid colonies may have been 1985). GRASSHOFF(1989: 201) considered that at overlooked. However, if so, their numbers would least one gorgonian amongst a particular expedi- probably not alter the overall finding that the hy- tion collection, Isidella elongata, 'reaches the droid faunae on oceanic islands tend to lack me- Ibero-Moroccan Gulf. ..by transport of larvae with dusa-releasing species. the Mediterranean water outflow' whence trans- Regrettably, insufficient is known of the lon- port to the Azores region is possible in the sub- gevity of leptolid planulae to determine whether surface gyres described above. BAKER (1967; or not those of the shallow-water Azorean species Table 6 Comparison of percentage of leptolid species having fully developed hydromedusa and not, between continental-coastal and oceanic-island faunae.

a b c d e Area Source No. of species No. of species No. of species % having Species with releasing planula releasing fully releasing hydro- fully devel- unpredicted or short-lived developed medusa and hav- oped hydro- dispersive medusoid hydromedusa ing hydroid medusa method known to raft (bxlOO)l(a+b)

i) Continental-coastal faunae Southern Africa MILLARD 1975 182 U.S.S.R. former NAUMOV1969 223 British Isles RUSSELL 1953, 93 1970; CORNE- LWS (in press); CORNELIUS & RYLAND 1990; some data original ii) Oceanic island faunae Bermuda, CALDER 1988, 47 excepting 1991 Plumulariidae s. lat. Fiji, GIBBONS & 24 excepting RYLAND 1989 Plumulariidae s. lat. Hawaii N~G1905, 52 EDMONSON 1930, COOKE1977 New Zealand RALPH 1957, 110 1958,1961a, b Enewetak Atoll Coom 1975 16 Azores Present paper above lOOm 28 below lOOm 41 Totals and percentages in parentheses score rafting species having a medusa stage (column c) as non-medusoid species (added to column a). This assumes that the medusa is not essential for longdistance dispersal in such species. Thus the percentages in parentheses in column d show best the relative fall in medusa-releasing species in oceanic-island faunae. The analysis is limited by inconstant taxonomy and differing faunal coverage between the works cited. In most areas anthomedusadathecate species are less well known than the typically more conspicuous leptomedusae/thecates. From Bermuda and Fiji no data were available on the speciose and non-medusoid Plumulariidae. Species in which the main dispersive stage has not been predicted are excluded from the calculations (column e). The data from Hawaii may be biased by the inclusion of several invalid nominal species of non-medusa releasing thecates described by NU?TING (1905) and by four nominal species of Eleutheria. The essentially non-dispersive medusa-releasing Cladonema and Eleutheria auct. ire included in column (a). The figures should be interpreted against the background of those for medusa suppression in all leptolids (Table 7). Table 7

Correlation among leptolids between reduction and suppression of the medusa stage and possession of large, branching colony. i) DISPERSIVE STAGES IN 'NORMAL' GENERA (i.e. excluding Stylasteridae, Velelloidea, Milleporida, and fossil forms) 1) Releasing fully-developed hydromedusa 217 (56%) 2) Releasing short-lived medusoid 17 (5%) 3) Releasing planula 127 (33%) 4) Dispersive stage unknown 27 (7%) 5) Total 'normal' genera 388 ii) DISPERSIVE STAGES IN GENERA HAVING LARGE AND/OR ARBORESCENT COLONY 1) Releasing fully-developed hydromedusa 8 (7.5%) 2) Releasing short-lived medusoid 6 (5.5%) 3) Releasing planula 9 1 (86%) 4) Dispersive stage unknown 1 (1.O%) 5) Total large and/or arborescent genera 106

The figures are numbers of genera. Since the reproductive pathways of only a minority of the species are definitely known, the table is somewhat hypothetical: but not much. Thus assumptions, for example, that all the Sertulariidae will prove to lack a medusa stage will probably be so close to reality that the overall pattern shown bv information collected so far will be found broadly unchanged. (Data from BovnLo~,1985; after CORNELIUS, present Table 2) considered that a taxonomically tline. Similarly, of 99 coastal species of fish then problematic hydromedusa, Zanclea costata s. str., known from the Azores BRIGGS (1974) con- had come from the Mediterranean where he con- sidered 77 to occur also on Euro-African coasts sidered it endemic. A hydroid, Laomedea pseu- and none at all to be common with the Americas. dodichotoma, known only from the Euro-African He found 21 to occur across the Atlantic, and one coast and the Azores, is mentioned here (Table 2) Azorean endemic. One family of intertidal gastro- but the absence of Caribbean records may simply pods present in the Azores has been shown to reflect its having been overlooked. Only one other have European faunal origins (GOFAS1990). study of cnidarians of the region has compared the The marine thalloid algae are better known fauna with eastern and western faunae. GRASS- across the North Atlantic Ocean than many animal HoFF (1981) studied bathyal (360-2200 m depth) groups. One analysis indicated that the Azorean gorgonians and pematulaceans and found in the algal flora is more similar to that of the other Ma- region 6 east-Atlantic forms, 2 west-Atlantic, and caronesian Islands (Canaries, Salvage Isles and 6 known from both east and west: on his small Madeiia), the Euro-African coast and especially sample size, quite inconclusive of a tendency to the Mediterranean, particularly as regards originate from east or west. In addition, for ba- wanner-water species, than to that of North thyal fauna there is essentially no dispersal barrier America (PRUD'HOMMEVAN REINE 1988). An- from either direction and comparison with the other study, not contradictory though some have possible origins of shallow-water faunal compo- taken it as so, concluded that the greatest simi- nents is limited in value. larity was with the flora of the cool New England All of the 18 species and subspecies of echino- coastline and that Azorean algae were floristically derms reported from the Azores by MARQUES distinct from all other temperate North Atlantic (1983) were forms already known from the Me- florae (RmEY & al. 1990). Prud'homme van diterranean region and adjoining Atlantic coas- Reine's data and conclusions were not available to Tittley when the latter submitted his paper (I. Tit- and hence paradoxically sometimes to traverse tley, pers. commn), and the Mediterranean algal greater distances than their corresponding free- flora was not included in Tittley's analysis. The swimming stages (RALPH 1961 c, CORNELIUS two studies suggest that there are many algal 1981, 1990b, 1991; reviews of rafting in all species in the Azores common on the one hand groups in HIGHSMITH1985, JACKSON1986, and with New England and on the other, and to a JOKIEL1989, 1990; discussion and review of re- greater extent, with the Mediterranean. cent dispersal literature in JOHANNESSON1988). The currents of western origin travel on the Substantial amounts of flotsam cross the At- surface and those from the other directions, most lantic carrying and dispersing non-swimming importantly perhaps the Mediterranean Water, forms. GUPPY(1917: 460-462) summarised drift- travel at several hundred metres depth. An interes- bottle and other evidence suggesting that aII sur- ting analysis would be to determine if species face flotsam arriving in the Azores came from the present in the Azores which were identifiable with w and NW,never from the E, at all seasons of the particular areas of origin had dispersive stages Year- able to travel at the depths of the currents which Some evidence is available on how long trans- may have brought them. Thus the idea of BRIGGS atlantic transport might take. GUPPY(1917: 472) (1974) that the major currents to the region may cited the case of a waterlogged and half-sub- have changed over a post-glacial or slightly longer merged schooner that took six months to drift time-scale might be tested. However, some from Newfoundland to the Hebrides 'covering the species usually regarded as surface forms can evi- last 550 miles [880 km] at ten miles [16 km] a dently disperse at depth. Thus the 'normally coas- day'. The Gulf Stream current off Bermuda tal' hydroid Clytia gracilis has been found at- reaches 9 km~h,averaging a substantial 2 kmh. tached to a structure moored in mid-water at 1443 The time taken for pelagic larvae to drift between m over the Wyville-Thompson Ridge at 60" 13' the Bahamas and NW Africa, implicitly passing N, 9" 13' W, some 300 km Nw of the Outer He- the Azores on the way, is thought to be 200-400 brides (BMNH collection 1985.10.2.16). Clearly, days (review in JACKSON1986: 595). Although species with narrower vertical distributions should some planktotrophic anthozoan planulae might be selected for such an analysis. postpone metamorphosis for this length of time The Caribbean and United States coastlines (P.G. Tranter, pers. commn; WERNER1984; PE- may seem the most likely origin of the shallow CHENIK 1990; discussion in CORNELIUS1992) it water Azorean hydroid fauna, cdmprised as it is of seems unlikely that a lecithotrophic leptolid one many rafting species which would presumably would. For hydroids lacking a medusa stage raft- travel mainly at the surface. But, as already noted, ing seems the only feasible way of reaching since there is little leptolid faunal difference be- remote oceanic islands. tween east and west Atlantic the origin of their Even some adult bivalves and gastropods are Azorean faunal component cannot be deduced by thought to hatre rafted between oceanic localities simple comparison. The clear demonsttation of (summaries in SCHELTEMA& WILLIAMS1983: faunal origins of several groups from the east 560, JOHANNESSON1988, and JOKIEL 1990). must from our present knowledge leave that of the Regular trans-oceanic drifting of entire trees, even Azorean leptolid fauna an open question. carrying rocks entwined in their roots, to remote oceanic islands has long been known to occur ii) Rafting. If the voracious, shallow-water hy- (DARWIN1906, to the Marshall Islands; literature dromedusae are in general too short-lived to cross cited by RALPH 1961c, to New Zealand; and re- from the coasts of the Americas to the Azores view by JOKIEL1990). then their lecithotrophic, non-feeding planulae Ralph considered recruitment of hydroids by must surely be unable to make tpe journey. But rafting from Australia to New Zealand to be the sessile stages of many benthic invertebrates, possible but, however, thought that from South including hydroids, are known to raft on floating America eastwards to the Australasian region the debris, algae, turtles, maybe some whales, and distance was too great. Possibly there are distance fish (especially on their crustacean ectoparasites); lhnitations even for rafters. The fauna of St Paul's Rocks is evidently somewhat Brazilian in compo- gaudichaudi sens. CORNELIUS1979, Tridentata sition, accounted for by EDWARDS& LUBBOCK distans, Antennella secundaria, Halopteris ca- (1983a, b) by their being closer to Brazil than Af- tharinu, Kirchenpaueria similis andlor K. pinnata rica. (see Table 4), Plumularia setacea, Ventromma Some cautionary evidence was presented by halecioides, and Aglaophenia pluma s. lat. A LEAL& BOUCHET(1991) who studied gastropod number of other species, such as the poorly distributions along a chain of seamounts trailing known Silhouetta uvacarpa and Clavopsella nuvis about 1000 km eastwards from Brazil. They (p. 88), might also be included. This list is not ex- showed that distance of colonization tended not to haustive: for example some.of the species listed as be related either to dispersive ability or to lack of near-cosmopolitan by STEPANYANTS(1980) may it. As the number of species tailed off away from prove to be rafters occurring on oceanic islands. the continental coast the proportions of long-dis- But on the remote Enewetak Atoll so much as half persers and short-dispersers remained, paradoxi- of the admittedly short hydroid faunal list com- cally, broadly similar. They concluded this was prised species from it (cf. COOKE1975). Most of due to successful rafting by all forms. However, the species just listed have been recorded rafting, this is certainly not paralleled by the leptolid fau- and all except Filellum serpens are substrate nae of remote island groups (Table 6; discussion generalists. This species is epizoic on a range of below). other hydroids, and may be able to disperse in this BRIGGS(1974), HIGHSMITH (1985), JOKIEL way. F. serratum occurs on a range of substrates (1989, 1990) and others were apparently right to (CALDER1991). regard rafting as a common phenomenon account- These 30 or more species form the bulk of the ing for many interrupted shallow-water marine Azorean shallow-water hydroid fauna as they do distributions. The role of rafting in the dispersal of around many warm- to cool-water oceanic islands hydroids has been discussed previously (CORN- world-wide. REES & WHITE (1966: 28 1) were per- ELIUS 1981; also 1982, 1991). JACKSON(1986) haps following the conclusions of RALPH (1961~)~ went further in concluding rhat beyond dispersal based on her New Zealahd work, when suggesting of a few thousand metres rafting may be the com- that 'many of the Azorean shallow-water species monest means of dispersal in both clonal and aclo- collected [before they wrote] seem to belong to a nal invertebrates. The high incidence of rafting fauna dispersed by ocean currents. Thus campanu- and non-medusoid species in the Azores coastal lariids attach to Sargassum and other weeds. Only leptolid fauna is thus noteworthy. further collecting will determine whether the fauna is poor in spaies without means for long- D. A species club range dispersal.' Present information indicates that this is so. Many of the shallow-water hydroids occurring in The few dozen rafting species involved form the 'Azores are typical of oceanic islands and, what might be described as a 'species club'. Its based on existing taxonomy, seem nearly cosmo- members apparently have in common the ability politan in coastal waters within their normal lati- to cross oceanic distances too great for spanning tudinal ranges (cf. papers cited in part ii of Table by a relatively short-lived planktonic stage 6). They include: Tubularia spp. (e.g. T. crocea, whether planula or medusa. The species seem Pennaria disticha), certain Eudendrium spp., often to disperse instead, perhaps 'accidentally' possibly Sarsia tubulosa (see p. 88), Filellum ser- but perhaps not, by rafting on floating and pens, F. serratum, Lafoea dumosa, Halecium te- swimming substrates. The concept of a 'club' par- nellum, Lafoeina tenuis, Campanularia hincksii, allels that of a species guild (as redefined by JAK- Laomedea calceolifera, L. flexuosa, four Obelia SIC 1981) in which the members pursue a com- spp., possibly Orthopyxis crenata, 0. integra, cer- mon activity such as predation on a well defined tain Clytia spp. including C. gracilis, C. hemis- class of prey. The 'club' differs from this, perhaps phaerica and C. linearis, Dynamena comicina, slightly, in comprising a recognisable assemblage possibly D. disticha, Sertularella spp. including S. of unrelated species which co-occur in a number of isolated geographical localities. Species from other groups may well belong to this 'club' but BOERO, F., & M. SA~1987. Motile sexual stages and are not considered here. Unlike a guild, in such a evolution of Leptomedusae (Cnidaria). - Bolletino Zoologica 54:131-139. 'club' there may be no advantage in or conse- quence of the grouping and the species do not BOUILLON, J. 1985. Essai de classification des hydro- polypes-hydromCduses (Hydrozoa-Cnidaria). - necessarily interact. InahMalayan Zoology 229-243. BOURY-ESNAULT, N. & M. T. LOPES 1985. Les dC- ACKNOWLEDGEMENTS mosponges littorales de I'archipel des A9ores.- An- nales de l'lnstitut Oc6anographique [Paris] (New I am grateful to Profs J. Bouillon and W. Vervoort, and Series) 61(2):149-225. to Drs D. R. Calder, H.R. Martins, S. J. Hawkins and R. BRIGGS, J.C. 1966. Oceanic islands, endemism, and B. Williams, for criticisms of the manuscript. Certain marine paleotemperatures. - Systematic Zoology other acknowledgements are made in the text. 15:153-163. I am grateful also to the joint leaders of "Expedi- tion Azores 1989", Drs Ricardo Santos and Stephen BRIGGS, J. C. 1974. Marine Zoogeography. McGraw- Hawkins, for much encouragement and for providing Hill,New York. 475 pp. necessary facilities. I was fortunate to receive also tire- CALDER, D.R. 1971. Hydroids and hydromedusae of less help and valuable advice from Dr Helen Martins southern Chesapeake Bay. Virginia Institute of and her husband Dr JosC Martins; and from Dr Eduarda Marine Science. Special Papers in Marine Science Goulart (DOPH) and her husband Rui during a three- 1:i-xiii, 1-125. day excursion to Caldeira de Santo Cristo on SbJorge. Preparation of the published account was not part of my CALDER, D.R. 1988. Shallow-water hydroids of Ber- official duties and had, therefore, to be done in my own muda. The Athecatae. - Life Sciences Contributions time. I am grateful to my family for their unfailing [Royal Ontario Museum] 148:i-iv, 1-107. tolerance of this; and to Graham Cornelius for much ad- CALDER, D.R. 1991. Shallow-water hydroids of Ber- vice on computers during word processing of the text. muda. The Thecatae, exclusive of Plumularioidea. Lucilia Dias drafted the Portuguese abstract. 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The hydromedusae of the Am- Silicularia gracilis Meyen, 1834 sterdam Mid North Atlantic Plankton Expedition. 1980 (Coelenterata. Hydrozoa). - Beaufortia S. bilabiata (Coughtrey, 1875) 32(3):27-56. Campanularia hincksii Alder, 1856 Clytia gracilis (M. Sars, 1850) Accepted 3 August 1992 Clytia hemisphaerica (Linnaeus, 1767) Clytia linearis (Thornely, 1899) Laomedea angulata Hincks, 1861 Laomedea calceolifera (Hincks, 1871) APPENDIX Laomedea jlexuosa Alder, 1857 Laomedea pseudodichotoma Vervoort, 1959 Classification and original authorities for scien- tific names of leptolid species mentioned. The list Obelia bidentata (Clarke, 1875) is not a checklist of species recorded from the Obelia dichotoma (Linnaeus, 1758) Azores region. Species mentioned only in Table 4 Obelia geniculata (Linnaeus, 1758) are not included. Works cited in this section are Obelia longissima (Pallas, 1766) not necessarilly included in the reference list but 'Tubularia clytoides Freycinet, 1824' (?=Obelia are as indicated in RALPH (1957), KRAMP(1961), sp., discussion in CORNELILIS1982: 118- 1 19) MILLARD (1975), VERVOORT (1987), CALDER Orthopyxis crenata (HaRlaub, 1901) (1988, 1991), PETERSEN(1990), CORNELIUS Orthopyxis integra Macgillivray, 1842 (1975a, 1979, 1982) and SVOBODA& CORNELIUS SERTULARIIDAE (199 1). Amphisbetia operculata (Linnaeus, 1758) Diphasia cf.attenuata (Hincks, 1866) ii) Hydromedusae Dynamena cornicina McCrady, 1859 CALYCOPSIDAE Dynamena distich (Bosc, 1802) Calycopsis typa Fewkes, 1882 Dynamena pumila (Linnaeus, 1758) Sibogita geornetrica Maas, I905 Sertularella gaudichaudi ouroux, 1824) [see CORNELNS 1979: 321y Stomotoca rugosa Mayer, 1900 (=Amphinema) Sertularella gayi (Lamouroux, 1821) PANDEIDAE Sertularella polyzonias (Linnaeus, 1758) Pandea conica (Quoy & Gaimard, 1827) ZANCLEIDAE Sertularia indivisa Meyen, 1834 (see present p. 77) Zanclea costata s. str. Gegenbaur, 1856 Tridentata distans (Lamouroux, 18 16) LAODICEIDAE PLUMULARIIDAE HALOPTERIINAE Krarnpella dubia Russell, 1957 CAMPANULARIIDAE Antennella secundaria (Gmelin, 179 1) Clytia hemisphaerica (Linnaeus, 1767) Halopteris catharina (Johnston, 1833) CUNINIDAE KIRCHENPAUERENAE Cunina duplicata Maas, 1893 Kirchenpaum.apinnata (Linnaeus, 1758) SOLMARISIDAE Kirchenpaueria similis (Hincks, 1861) Solmaris corona (Keferstein& Ehlers, 1861) PLUMULARIINAE GERYONIIDAE Nemertesia ramosa Lamourom, 18 16 Lirio e tetraphylla (Chamisso & Eysenhardt, Plumularia setacea (Linnaeus, 1758) lf21, Ventromma hlecioides (Alder, 1859) RHOPALONEMATIDAE AGLAOPHENIIDAE Aglaura hemistomu Pkron & Lesueur, 18 10 Aglaophenia acacia Allman, 1883 Rhopalonemu velatum Gegenbaur, 1856 Aglaophenia picardi Svoboda, 1979 Aglaophenia pluma (Linnaeus, 1758) Aglaophenia tubulifera (Hincks, 1861)