BULLETIN OF MARINE SCIENCE, 46(2): 406-424, 1990

SHORE (CIRRIPEDIA, THORACICA) AND A REVISION OF THEIR PROVINCIALISM AND TRANSITION ZONES IN THE TROPICAL EASTERN PACIFIC

Jorge E. Laguna

ABSTRACT The emergence of the Isthmus of Panama separated the Caribbean from the Tropical Eastern Pacific (TEP) and played a major role in the biogeographical development of the tropical and latitudinal marine provincialism seen today. Latitudinal provincialism in the Tropical Eastern Pacific has been assessed in terms of the distribution of a variety of taxa. A detailed study of the barnacles provides a basis for a refined model for the provincial associations observed. Closer attention needs to be paid to transition zones, and as it turns out, the GuifofCalifornia is not a province as strictly defined, but an extension of a transition zone. Provincial asso- ciations are defined in terms of the barnacles of the Tropical Eastern Pacific, and are compared with those known for other taxa.

From the early Oligocene to the late Pliocene the Atlantic and Pacific Oceans were connected through the Panamic Strait and, by shallow water circulation, biotic exchange took place between them (Van Andel, 1979; Keigwin, 1982; Valentine, 1971; 1973). Because of the transport of planktonic larvae of sedentary forms by equatorial currents, the fauna of both oceans remained very similar until the late Miocene (Woodring, 1966). With the tectonic closure of the Panamic Isthmus, and an increase in the Caribbean temperature (about 5.7 my B P), a modem hydrographic setting and circulation were established (Emiliani et a1., 1972; Keigwin, 1982). The physical changes brought about by this geologic event separated the biota of both oceans, causing the extinction of some species, survival of others, and the evolution of new ones. This is indicated by the fact that some species are still found on both sides of the Isthmus and others have survived in either the Pacific or the Caribbean. The Tropical Eastern Pacific, a larger and more open body of water than the Caribbean, was less affected (had fewer extinctions) by the physical changes produced by this uplift (Woodring, 1966). These changes led to the present marine tropical provincialism found in these oceans (Ekman, 1953). The Tropical Eastern Pacific was defined by Ekman (1953) as the region ex- tending from the southern tip of western Baja California (23°N) and the Gulf of California to the Gulf of Guayaquil (3-4°S). Transitional subtropical faunas were defined between southern Baja California and San Diego (23-33°N) in the north, and between Ecuador and Peru in the south (3-6°S; Ekman, 1953). A number of modified definitions have been given (Cromwell and Bennett, 1959; Abbott, 1966; Zullo, 1966; Briggs, 1973), but these remain basically the same as Ekman's (1953). However, Valentine (1966; 1973) found that the northern transition zone between tropical and temperate molluscan species was further south (20-28°N, Valentine's Surian Province). Brusca and Wallerstein (1979) came to the same conclusion based on isopod data (24-28°N). This also seems to be the case for the barnacles. The Tropical Eastern Pacific has also been described as the region lying between the 20°C isotherms (Abbott, 1966; Valentine, 1966; 1973). The thermal tolerance

406 LAGUNA: PROVINCIALISM, EASTERN PACIFIC 407 of an organism is often related to temperature optima for enzyme systems, and temperature often regulates reproductive cycles (Newman and Abbott, 1980). Subtropical faunal breaks are mainly regions of rapid thermal change associated with discontinuity in the coastal surface currents (Abbott, 1966). These regions lead to changes from one faunal association to another and are referred to herein as transition zones. Similar circumstances can occur in the tropics. Off Guatemala for example, two thermally distinctive water masses converge (Cromwell and Bennett, 1959; Abbott, 1966) giving rise to appreciable biotic changes (Valentine, 1973). Until the work of Laguna (1985; 1987) there was no major unifying study of the balanomorph barnacles from the Tropical Eastern Pacific, as evident from the depauperate literature for this region. An earlier attempt to compile this knowledge was made by Zullo (1966), but at that time, there were only 57 species ofbalanomorph barnacles known from the entire eastern Pacific, seven of which were assigned to the Tropical Eastern Pacific. This number has now increased to more than 50 species for the TEP, excluding whale and turtle barnacles. Of the 57 tropical species, 28 range throughout the Panamic Province s.1.(the tropics). The rest are restricted to members of northern and southern overlapping sub- tropical provinces (Californian, Mexican, and Peruvian Provinces; Table 1, Fig. 1).

METHODS

All collections used for this study are housed in the Benthic Invertebrate Collections of the Scripps Institution of Oceanography, La Jolla, California, except the Jorge Laguna collection which is at the National Museum of Natural History, Washington, D.C. (Laguna, 1985). The major lots are: Scripps Institution of Oceanography-Smithsonian Tropical Research Institute (SIO-SI 1971-1973) collection: a survey of intertidal barnacles on both coasts of Panama, mostly in areas adjacent to the Panama Canal (Laguna, 1985, appendices I, II). Tropical Eastern Pacific Expedition (TEPE-1978) collection: a general survey of 47 stations found between the Gulf of Panama and the Gulf of California (Laguna, 1985, appendix II). Kathy DeReimer collection (1980): miscellaneous collections on the Pacific coast of Central America, and some sites on the Atlantic coast (Laguna, 1985, appendix II). Jorge Laguna collection (1984): a survey of the intertidal barnacles from the Pacific and Atlantic coasts of Panama (Laguna, 1985, appendix I). These collections make Panama the best sampled region for barnacles in the Tropical Eastern Pacific. In addition to the collections, available literature on cirripeds from this region was utilized for de- termining species ranges (Darwin, 1851; 1854; Pi!sbry, 1916; 1918; Rogers, 1948; Zullo, 1966; Henry and McLaughlin, 1975; Newman and Ross, 1976; Southward and Newman, 1977). The ranges of species of Tropical Eastern Pacific Cirripedia were plotted (Table I, Fig. I). Ranges of some non- cirriped taxa known from the literature are available for comparison with those of thoracic Cirripedia in the Tropical Eastern Pacific (Table 2, Fig. 2). These latitudinal ranges have been used to determine provincial associations in the TEP. Barnacle species cluster latitudinally. The regions between cluster of species constitute faunal breaks. The faunal breaks have regions of overlap referred to as transition zones, and form the basis for defining the faunal provinces. Each province has a group of endemic species, and wide-ranging species from other provinces. The number of species mentioned as belonging to each province corresponds to the endemic portion found there. Many authors have previously used the concepts of "province" and "transition zone" (Valentine, 1966; 1973; Briggs, 1974; Newman, 1979b; Brusca and Wallerstein, 1979). Some confusion on their use exists due to the lack of a unifying general definition. A marine province as envisaged in this paper, is a relatively large region encompassing a variety of habitats and a diversity of communities. A province has a characteristic high number of endemic species (45% or more; derived from the percent endemic versus the total number of species found in each province) that overlap to varying degrees those of adjacent provinces; but the substantial endemic portion distinguishes it. The region constituting a province is apparently determined primarily by physical factors (Valentine, 1966; 1973; Dolan et aI., 1972), although biological factors may be im- portant (Newman, 1979b; Brusca and Wallerstein, 1979). A latitudinal transition zone is the region of overlap between two or more faunal provinces; it may 408 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990

Table I. Cirripedia of the Tropical Eastern Pacific grouped according to Provinces. For ranges of distribution see Figure I and Laguna, 1985

Group Provincial Associations Californian 1. Tamiasoma regalis (Newman and Foster, 1987) 2. Oxynaspis rossi Newman, 1972:202 3. Membranobalanus orcutti (Pilsbry, 1916:233) 4. Tetraclita rubescense (Darwin, 1854:462) 5. Megabalanus californicus (Pilsbry, 1916:65) 6. Chthamalus fissus (Sowerby, 1833:74) 7. Balanus pacificus pacificus (Pilsbry, 1916:104) 8. Pollicipes polymerus Sowerby, 1833:74 9. Balanus nubilus Darwin, 1854:253 10. Concavus aquila (Pilsbry, 1907: 199) 11. Balanus glandula (Pilsbry, 1916: 180) II Mexican 12. Chthamalus "cortezianus" (undescribed; Hedgecock, 1979) 13. Megaba/anus peninsu/aris (Pilsbry, 1916:66) 14. Tetraclita confmis (Pilsbry, 1916:255) 15. Balanus inexpectatus inexpectatus Pilsbry, 1916:97 16. Chthamalus anisopoma Pilsbry, 1916:317 17. Concavus panamensis eyerdami (Henry, 1960) 18. Membranobalanus n.sp. Newman, pers. comm. 1985 19. Acasta n.sp. Newman, pers. comm. 1985 20. Heteralepas n.sp. Newman, pers. comm. 1985 21. Balanus parkeri Zullo, 1967 III Amphitropical 22. Pollicipes elegans (Lesson, 1830:441) IV Panamic s.1. 23. Conopea galeata (Linnaeus, 1771:544) 24. Octolasmis californiana Newman, 1960b 25. Megabalanus coccopoma (Darwin, 1854:196) 26. Hexacreusia durhami Zullo, 1961 27. Balanus poecilus Darwin, 1854 28. B. pacificus mexicanus Henry, 1941: 109 29. Euraphia imperatrix Pilsbry, 1916:320 30. E. eastropacensis (deOliveira, 1940) Laguna 1987 31. Conopea masignotus (Henry and McLaughlin, 1967) 32. Chthamalus "mexicanus" (undescribed; Hedgecock, 1979) 33. Fistulobalanus suturaltus (Henry, 1973:983) 34. Megabalanus peninsularis ?n.subsp. (Pilsbry, 1916:70) V Panamic s. str. 35. Balanus inexpectatus panamensis Laguna, 1985 36. Megabalanus vinaceus (Darwin, 1854:213) 37. Tetraclita panamensis (Pilsbry, 1916:256) 38. Chthamalus panamensis (Pilsbry, 1916:319) 39. Tetrabalanus polygenus Cornwall, 1941:227 40. Balanus peruvian us Pilsbry, 1909:69 41. Catophragmus pilsbryi Brach, 1922:298 42. Heteralepas quadrata (Aurivillius, 1894) 43. Megabalanus peninsularis (former M. galapaganus Henry and McLaughlin, 1986) 44. Concavus panamensis panamensis (Rogers, 1948:95) 45. ?Solidobalanus hesperius laevidomiformis Kolosvary, 1941 VI Galapagonian 46. Hexacreusia straenleni Zullo and Beach, 1973 47. Membranobalanus nebrias Zullo and Beach, 1973 48. Octolasmis lowei (Darwin, 1851:128; ?O. californiana. Newman, pers. comm. 1986) LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIFIC 409

Table I. Continued ======::; Group Provincia) Associations 49. Oxynaspis n.sp. Newman, pers. comm. 1985 50. Tetraclita milleporosa (Pilsbry, 1916:257) VII Peruvian 51. Concavus henryae Newman, 1982 52. Jehlius cirratus (Darwin, 1854:321) 53. Austromegabalanus concinnus (Darwin, 1854: 196) 54. A. psittacus (Molina, 1788:223) 55. Chthamalus scrabosus Darwin, 1854:468 56. Balanus laevis Brugiere, 1789: 164 57. Verruca laevigata Sowerby, 1833 VIII Miscellaneous Introduced #; Cosmopolitan *; Deep water **; Turtle barnacle &; Acrothoracica && 58. Acroscalpelum californicum Newman, pers. comm, 1985 ** 59. Balanus amphitrite Darwin, 1854:240 #* 60. B. trigon us Darwin, 1854:240 * 61. B. improvisus Darwin, 1854:250 #* 62. Kochlorine hamata Tomlinson, 1969 && 63. Balanus eburneus Gould, 1841:15 # 64. Cryptophialus wainwrighti Tomlinson, 1969 && 65. testudinaria (Linnaeus, 1767) & 66. Balanus reticulatus (Utinomi, 1967:216 #* 67. B. calidus Pilsbry, 1916: 118 * 68. Fistulobalanus pal/idus (Darwin, 1854:240; Panama Canal locks) # 69. Chonchoderma virgatum (Spengler, 1790:207) & 70. Platylepas n.sp. Newman, pers. comm. 1985 & 71. Stomatolepas n.sp. Newman, pers. comm, 1985 & 72. n.sp. Newman, pers. comm. 1985 ** 73. Balanus ?cf. spongicola Brown, 1844: 121 # Additional literature: Birkeland et aI., 1975; Braltstrom and Johanssen, 1984; Coker, 1901; Henry, 1942; 1943; Henry and Mclaughlin, 1972; Hertlein, 1932; 1963; Hubbs, 1949; Jones, 1972; Newman, 1960a, 1979a; Newman and Ross, 1973; Newman and Southward, 1977; Nilsson-Cantell, 1957; Ross, 1962; 1969; Southward, 1983; Spivey, 1976; Utinomi, 1968; Zullo, ]963; 1968; 1969a; 1969h; 1972; 1984. contain a few short-range endemics. Transition zones generally have unstable environmental conditions and steep physical gradients; their boundaries are often seasonal, which in tum affects species com- position (Semenov and Berman, 1977). Transition zones (TZ) may correspond to temperate (Cali- fornian-Oregonian TZ), subtropical (Californian-Mexican, and Panamic-Peruvian TZ), or tropical regions (Mexican-Panamic TZ). Latitudinal transition zones tend to be broader in the tropics due to the relatively subtle or gradual changes in physical conditions there (e.g., Mexican-Panamic TZ). On the other hand, they are generally narrower in temperate regions (Californian-Oregonian, Newman, 1979b; Mexican-Californian, Panamic-Peruvian, this report), due to the steepening climatic gradients there, From the present study, it appears that the number of short-range endemic species ofa Transition Zone increases with latitude. If so, it may be due to the sharpness of biotic change which frees the resources upon which the short-range endemics depend. While the above definitions of Province and Transition Zone have been developed from the study of barnacles, they apparently fit the distributional patterns found for other marine organisms (Fig. 3; Valentine, 1966; Brusca and Wallerstein, 1979; Springer, 1982; Williams, 1986). Figure 3 is a com- pilation ofa variety of taxa and is intended to help illustrate, in addition to the barnacles (Fig. I), the extent of provinces in the Tropical Eastern Pacific.

REsULTS Thirty genera and about 60 species of thoracic cirripeds are known from the intertidal and shallow waters of the Tropical Eastern Pacific (4°S to 28°N), ex- cluding whale, turtle, and pelagic genera. The balanoids show the greatest diversity, followed by the chthamaloids. Eleven species also occur in the Californian Prov- ince, which overlaps with the northern limits of the tropical provinces, of these 410 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990

RANGES OF THORACIC CIRRIPEDIA

I 5 10 15 20 25 30 35 40 45 50 55 60 65 70 ~ 1 1 1 1 1 300N 1

':'. .. l~....:::: 24° GROUP I r

GROUP IT

." ::: : :. m

11111 ~ a.. ~ 11111 I GROUPISl GROUPJl GROUP~ GROUPWI o Northern Range outside of the Gulf of California Present • Northern Range inside of the Gulf of Calif Absent ...... -...... Possible + Species present extended range Figure I. Ranges of barnacle species in the Tropical Eastern Pacific. Arabic numerals above refer to species listed in Table I, and Roman numerals the provincial groups to which they belong. Note the region above 22°N, where open circles represent ranges on the west side, and closed circles on the east side (inside the Gulf) of the Peninsula of Baja California. LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIFIC 4] I

PROVINCIAL ASSOCIATION OF BARu'ACLES IN THE EASTERN PACIFIC -"\

GULF OF CALIFORNIA ISS] MEXICAN -- CALIFORNIAN B •••••••• MEXICAN r::z:lPANAMIC 5. L. -- PANAMIC5.L. 4 -- PANAMIC 5.5. - - - - PERUVIAN

Ul w 812 a.. Ul

* B

4

o

LATITUDE (EASTERN PACIFIC) Figure 2. Provincial associations for barnacles in the Tropical Eastern Pacific derived from Figure I. Note that in the Gulf of California there are species infiltrating from the Mexican and Panamic s.l. Provinces (upper left insert). five are not known to occur south of Punta Eugenia and Cedros Island (28°N), and the rest do not range further south than Cabo San Lucas (23°N; Fig. 1). In the south, seven species are extensions from the Peruvian Province, which over- laps with the southern end of the Panamic Province (and TEP). There are 11 tropical cosmopolites, including some recent introductions. The remaining 44 are endemic to the Tropical Eastern Pacific (Table 1, Fig. 1). Major faunal breaks for the barnacles were found at about 24°N, 16°N, and 4°S (Figs. 1-3). The ranges of barnacles (Table 1, Figs. 1, 2), as well as the ranges of a variety of other taxa (90 species; Table 2, Figs. 3, 4), indicate that the Peninsula of Baja California separates two transitional regions (Fig. 4). The western, or pacific side, is a warm-temperate to subtropical Transition Zone, while the eastern or Gulf side is subtropical to tropical. These are referred to herein as: 1) the "Californian- Mexican Transition Zone" (Surian Province of Valentine, 1966; Cortez Province in part of Briggs, 1974) between 22°N and 28°N on the west coast of Baja Cali- fornia; 2) the "Gulf Transition Zone" in the Gulf of California (Cortez Province in part, Briggs, 1974; Brusca and Wallerstein, 1979; Glynn and Wellington, 1983). This is evident from the overlapping faunal groups and short-range endemics found there (Figs. 1,3,4). Ten species of barnacles are endemic to the Mexican Province (14-26°N; Fig 1, Group II, Fig 2). Mexican species broadly overlap Panamic ones in the Mexican- Panamic Transition Zone (about 14°N to nOON; Figs. 2, 5). There are mostly Panamic species in this zone, plus a few Mexican and cosmopolitan species (Figs. 1, 2). Wide-ranging tropical species, not affected by the faunal breaks, were classified 412 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990

Table 2. Miscellaneous taxa used for studying generalized tracks of provincial associations in the Tropical Eastern Pacific. Species not arranged taxonomically, but by their relative latitudinal ranges (Fig. 3)

No. Taxon Reference·

I Idotea aculeata 14 2 I. stenops 14 3 I. urotoma 14 4 I. resecata 14 5 I. wosnesenskii 14 6 Synidodea harfordi 14 7 Mycteropoerca jordani I 8 Eucalanus californicus 12 9 Thysanoessa gregaria (bipolar) I 10 Panu/irus interruptus 4 11 Paraclinus integripinnis 3 12 Labidocera jollae (L. jollae group) 9 13 Euphasia pacifica 12 14 Colidotea rostrata 14 15 Stylocheiron maximum (circumtropical) 12 16 Euphasia diomedeae 12 17 Mycteroperca xenarcha I 18 Excorallana truncata 17 19 Temora discaudata 9 20 Batrachoididae (toadfish) 16 21 Cynoglossidae (tongue soles fish) 16 22 Rhizoprionodon (Carcharhinid shark) 16 23 Opistognathidae (jawfish) 16 24 Sciaenidae (fish family) 16 25 Trichiurus lepturus (trichiurid fish) 16 26 Torpenidiformes (elasmobranch order) 16 27 Sarda (scombrid fish) 16 28 Uranoscopidae (fish family) 16 29 Heterodontidae (hom-shark) 16 30 Branchiostegidae (tile fish) 16 31 Penaeus californiensis brevirostris 9 32 Labidocera johnsoni 9 33 Paraclinus sini 3 34 Excorallana bruscai 17 35 Labidocera kolpos (L. jollae group) 9 36 Notoacmea ubiquita 15 37 Mycteroperca rosacea I 38 Diplectrum labarum 8 39 D. pacificum 8 40 Starksia spinipenis 5 41 Diplectrum sciurus 8 42 Panu/irus inj/atus 4 43 Centropages furcatus 9 44 Paraclinus mexican us 3 45 Eucalanus inermis 12 46 Excorallana houstoni 17 47 Brachyuran crabs II 48 Diplectrum macropoma 8 49 Eusymmerus antennatus 14 50 Mycteroperca prionura 1 51 Colidotea findleyi 14 52 Xenomedea rhodopyga 5 53 Asteropteroninae (ostracod) 16 54 Scarus compresus 2 55 Callechelys eristigmus 6 56 Cleantis occidentalis 14 57 Pontel/ina sobrina 12 LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIFIC 413

Table 2. Continued

No. Taxon Reference· 58 Paraclinus beebei 3 59 Diplectrum eumelum 8 60 Callechelys cliffi 6 61 Excorallana occidentalis 17 62 Labidocera diandra (L. jollae group) 9 63 Starksia grammilaga 5 64 Paraclinus tanygnathus 3 65 Muraena clepsydra 10 66 Khulia taeniura 7 67 Pristidae (sawfish) 16 68 Cyclasteropinae (ostracod) 16 69 Paraclinus stephensi 3 70 Stylocheiron carinatum (circumtropical) 12 71 Generalized Stomatopods Distribution 11 72 Generalized Fish Distribution II 73 Notoacmea pumila 15 74 Starksia fulva 5 75 Litopenaeus vannamei occidentalis 9 76 Paraclinus monophthalmus 3 77 Mccoskerichthys sandae 13 78 Mycteroperca ol/ax 1 79 Lottia mimica 15 80 L. smithi 15 81 Notoacmea immaculata 15 82 N. rothi 15 83 Callechelys galapagensis 6 84 Anarchias galapagensis 10 85 Starksia galapagensis 5 86 Euphasiamucronata 12 87 Cypridinidae (ostracod) 16 88 Erichsonella cortezi 14 89 Paraclinus walkeri 3 90 P. magdalenae 3 • References: 1. Fish, Rosenblatt and Zahuranec, 1967; 2. Fish, Rosenblatt and Hobson, 1969; 3. Fish, Rosenblatt and Parr, 1969; 4. Lobsters. Johnson, 1971; S. Fish, Rosenblatt and Taylor, 1971; 6. Snake eels, McCosker and RosenbJatt, 1972; 7. Fish, Rosenblatt et al.. 1972; 8. Fish, Rosenblatt and Johnson, 1974; 9. Copepods, Aeminger, 1975; 10. Eels, McCosker and Rosenblatt, 1975a; 1975b; 11. Monophyletic components of biota, Rosen, 1975; 12. Euphausiids and copepods, Reid et aI., 1978; 13. Blenny fish, Rosenblalt and Stephens, 1978; 14. Isopods, Brusca and Wallerstein, 1979; 15. Limpets, Lindberg and McLean, 1981; 16. Mostly shore fishes, Springer, 1982; 17. Isopods, Delaney, 1984. Not included in the analysis (Fig. 3), but used for the interpretation of data: Ball and Haig, 1974; Briggs, 1961; Cheng and Schulenberger, 1980; Emerson, 1978; Flemingerand Hulsemann, 1973; Hayden and Dolan, 1976; Keen, 1971; Wicksten, 1979. as elements of the Panamic (s.l.) Province (Figs. 1, Group IV). From extensive collections and the literature, it was found that most of these species range from about 33°N (and inside the Gulf of California) to about 3°S. The shorter ranging eutropical species were grouped in the Panamic (s. str.) Province (Fig. 1, Group V), here defined as the region between the Gulf of Fonseca (13°N) and the Gulf of Guayaquil (3°S). All of the 12 species reported from the Panamic s.l. Province (Table 1, Group IV) widely overlap with the Peruvian, Mexican, Panamic s. str., and Californian provinces. Only 10 species seem to be restricted to the Panamic s. str. Province (Fig. 1, Group V). The Galapagos Archipelago has been recognized as having a unique biota with tropical, subtropical and temperate elements (Rosenblatt and Walker, 1961; Ab- bott, 1966; Briggs, 1974; Glynn and Wellington, 1983; Wellington, 1984), largely due to its unique hydrographic conditions (Wellington, 1984). Ofthe 10 recorded species of barnacles, four are endemic (Table 1, III; Figs. 1, 2). It is of interest to note that no chthamaloid barnacles have been reported (Hedgpeth, 1969; Wel- lington, 1984; Newman and Zullo, pers. comm., 1985). 414 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990

The Panamic Province (s.l.) overlaps at its southern limit with the warm-tem- perate Peruvian Province. The Panamic-Peruvian Transition Zone (3-6°S) seems to be the sharpest of all the Tropical Eastern Pacific TZs, probably due to the much colder and stronger influence of the Peruvian current and to concominant steep physical gradients. About 11 species are found in this transition zone, seven of which are from the Peruvian Province. The northern limit for most species of the Peruvian Province is in the vicinity of Tumbes, Peru (4OS;Fleminger, 1975; pers. comm., 1985).

DISCUSSIONANDCONCLUSIONS Several environmental barriers to dispersal are found along the coasts of the Tropical Eastern Pacific. Surface currents have been considered one of the primary mechanisms affecting dispersal (Ekman, 1953; Briggs, 1961; 1973; Glynn and Wellington, 1983). Currents may carry individuals to regions where they cannot reproduce or do not survive, due to their physiological adaptations (MacArthur and Wilson, 1967; Newman and Abbott, 1980; Newman and McConnaughey, 1987). But currents per se do not really determine the extent of a province. Therefore, steepening temperature gradients are considered the most important factor affecting the latitudinal distribution of provincial associations, Californian Province. - Most species belonging to the Californian Province (Figs. 1,3, Nos. 1-11) range south to Punta Eugenia (26°N). This is the case for copepods (Fleminger, 1975), molluscs (Addicott, 1966; Valentine, 1966; 1973), fish (Spring- er, 1982), and barnacles (Newman, 1979b; Newman and Abbott, 1980). South of Punta Eugenia, tropical forms begin to predominate (Valentine, 1966; 1973; Fleminger, 1975; Springer, 1982). The tropical shore-fish fauna extends to 25°N, western Baja California, and to 300N in the Gulf of California (Rosenblatt, 1967; Springer, 1982). This is also the case for molluscs (Addicott, 1966; Valentine, 1973), ostracods (Springer, 1982), cope pods (Fleminger, 1975; pers. comm., 1985), and most tropical barnacles (Tables 1, 2; Figs. 1-3). CALIFORNIAN-MEXICANTRANSITIONZoNE. The Gulf of California has previ- ously been called a province (Briggs, 1974; Brusca and Wallerstein, 1979), but present analysis shows it is actually a transitional region between provinces. If we separate species according to provinces to which they belong, it is observed that the marine fauna on both sides of the Peninsula of Baja California is for the most part represented by species from several provinces (Figs. 1, 3-5). The Gulf of California is confined and the southern half has relatively uniform environments (mudflats to the east, and rocky coast on the west). In terms of physical conditions, the northern third of the Gulf is a mostly unstable region (McCourt et al., 1984). There are drastic changes in temperatures during the summer and winter months with winter kills of some of the biota (Soule, 1960; Walker, 1960; McCourt et al., 1984), and southward migration of some organisms as fish (Rosenblatt, pers. comm., 1985). Unstable conditions are characteristic of most transition zones (Semenov and Berman, 1977), as they are for the Gulf of California. The Gulf does not have many endemics (especially barnacles). Most species are members ofthe Panamic, Mexican and Californian Provinces (Figs. 4,5). The species found on both sides of Baja California include transition zone endemics and elements endemic to the Gulf. This makes the Peninsula of Baja California a Transition Zone, both inside (to 32°N) and outside the Gulf (to 28°N; Figs. 4, 5). If a barrier were built at the mouth of the Gulf of California, very few species LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIFIC 415

RANGES OF MISCELLANEOUS TAXA

I 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 ! ! ! ! 1 1 1 1 j j I -

I I I : : I I III I I 'III I. t I II ::I' '1-:'III II It I I:::" ::: nl::: ,I ••• I II : I. ,I ". II " ::' II .1 lit I I ; I I I I I I

i'l II .":::

IIIlIII II

o Northern Range outside of the Gulf of California - Present • Northern Range inside of the Gulf of California Absent x Species present Possible extended range Figure 3. Ranges of a variety of species in the Tropical Eastern Pacific. Species are not grouped taxonomically, but rather by latitudinal range. Arabic numerals above correspond to the taxa given in Table 2. of barnacles would become extinct. We would expect to lose the short-range, transition zone Gulf endemics, since the depauperate upper-gulf region is where most endemics are found taking over the empty niches there (Figs. 3, 4; Walker, 1960; Briggs, 1974; Williams, 1986; Fig. I). Many workers have recognized the strong affinity of the GulfofCalifornia with the Panamic Province (Dawson, 1960; Soule, 1960; Walker, 1960; Fig. 4). In fact, the high diversity derived from overlapping faunal associations will lead the casual observer to think of the Gulf as a faunal province. But placing the overall situation in perspective, it is observed that we are dealing with multi provincial infiltrations 416 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990

FAUNAL ELEMENTS

Figure 4. Distribution of the provincial and transition zone species of the Baja California region, derived from Figure 3 and Table 2. The numbers within each faunal element represent the species found at that given latitude.

into the Gulf (Figs. 4, 5). The Gulf is a unique place and some degree of endemism is expected, but it does not fit the general definition of a province. Mexican Province. - This Province was first recognized by Briggs (1974) as the region from Cabo San Lucas to Tangola- Tangola Bay (Gulf of Tehuantepec). Members of the Mexican Province (Surian in part, Valentine, 1966; Cortex in part, Briggs, 1974) appear most closely related to those of the Panamic tropical fauna. This province extends from about 14°N to about 26°N (one barnacle species ranges to 32°N; #12 on Fig. 1), where it overlaps with the Californian Province on the western coast of Baja California (Figs. 1, 2). A high degree of endemism (50%) is reported for barnacles of the Mexican Province at 24°N. Most species of this province range into the Gulf of California and to 28°N on the west coast of Baja California (Figs. 2, 4, 5). The southern limit for most Mexican species seems to be around 20oN. Few of these species extend south to 14°N where they overlap with "Panamic s. str." species (Figs. 1-5). MEXICAN-PANAMICTRANSITIONZoNE. This region appears to be the broadest LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIAC 417

PROVINCE AND TRANSITION ZONES OF THE EASTERN PACIFIC

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PANAMICS,S, lito 3o'S-:J Figure 5, Histograms of provincial and transition zone designations for the Tropical Eastern Pacific. The proposed model emphasizes the importance of transition zones, as did Soule (1960), especially for interpreting the situation in the Gulf of California. The 'Galapagos Sub-province' and the Peruvian- Panamic Transition Zone are not included for simplicity. 418 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990 transitional area (about l4°N-20°N) in the Tropical Eastern Pacific, in terms of degrees of latitude and geographic area. The faunal gap and faunal uniformity concerning fishes (Springer, 1958; Rosenblatt, 1967) recognized earlier for this region, is probably due to the uniformity of the coastline, and decreased habitat diversity (Dolan et aI., 1972; F1eminger, pers. comm., 1985). This "gap" is ap- parent in other taxonomic groups (Fig. 3, dashed lines #20-30). The region seems to act as a barrier to dispersal for "Mexican" and "Panamic" species, as few appear to cross it. Therefore, there is not much overlap ofPanamic and Mexican species, even though the area is regarded as a wide transitional region (Figs. 1, 2). Barriers to dispersal between these northern and southern regions have been proposed. Abbott (1966) concluded that the winter currents, flowing south from the general area of San Jose de Guatemala, acted as a barrier to dispersal north and south of this region. Springer (1958) and Rosenblatt (1967) proposed that the "depositional shoreline" from Salina Cruz (Mexico) to the Gulf of Fonseca (Nicaragua) acted as a barrier to the distribution of many species of rocky shore fishes. Actually, the region of the barriers includes the end of one provincial association and the beginning of another; therefore, previous workers were looking at the Mexican-Panamic Transition Zone, where northern Mexican species start dropping out and southern Panamic s. str. ones begin to take over (Fig. 2). It is known that Pollicipes elegans (Lesson, 1830:441) is found in this region in addition to other transition zones. It is also important to note that Megabalanus peninsularis (Pilsbry, 1916:70; a subtropical form) exists as a short-range tran- sition zone species in the Tropical Eastern Pacific. Specimens were collected in several localities on the TEPE-78 Expedition (Table 1, Fig. 1, #34). It was probably not introduced, because TEPE collections were coastal, distant from sea ports, and M. peninsularis is not a fouling form. It is interesting to note that this species is abundant in southern Baja California (a transition zone), and is now reported in the Mexican-Panamic Transition Zone.

Panamic s.l. Province. - This province consists ofPanamic species that range north of the Mexican-Panamic Transition Zone, and south to the Panamic-Peruvian Transition Zone. Some ofthe Panamic s.l. species range far into the Mexican and even temperate provinces (Figs. 1, 2, 5). However, these eurytopic species are not considered members of these temperate and subtropical provinces because they do not reflect their provincial limits. The southern limit (4-6°S) for this province is essentially the same as for the Panamic s. str. Province.

Panamic s. str. Province. - Most species of this province seem to be restricted between 4°S and 14°N (Figs. 1,2,5). Briggs (1974) recognized this province as the area between Tangola- Tangola Bay (16°N) and Cabo Blanco (50S). The Pan- amic s. str. Province has a total of 10 (? 11) barnacle species, four of which have short ranges (Figs. 1, 2). The questionable number reflects the record of Solidobala- nus hesperius laevidomiformis (Kolosvary, 1941), because this North Pacific, cold- temperate species has never been found again, and the original types are lost; thus the record is doubtful. A high degree of endemism (48%) is reported here for barnacles of the Panamic s. str. Province at about 8°N.

The Galapagos Sub-province. - The Galapagos Archipelago, between ION and 1°30'S (Abbott, 1966), has been recognized as a region with a high degree of endemism for many marine organisms (Abbott, 1966; Rosenblatt, 1967; Briggs, 1974; Lindberg and McLean, 1981). Recent work (James, 1984) suggests that LAGUNA: BARNACLE PROVINCIALISM, EASTERN PACIFIC 419 endemism is not as common in the marine invertebrate fauna as in the terrestrial biota. An endemism of about 30% is reported for the barnacles. This number may increase if extensive collections become available. In this report, the Galapagos are thought of as a Subprovince of the Panamic s.1. (Abbott, 1966; Briggs, 1974; James, 1984), and Panamic s. str. provinces. Most marine species are transported primarily by currents flowing from Ecuador, the Gulf of Panama, and Colombia, in order of importance (Abbott, 1966; Glynn and Wellington 1983). There are no major, strong currents flowing from the Galapagos to the mainland (Abbott, 1966; Glynn and Wellington, 1983), thus reducing the possibility of transport to the mainland. Insular species shared with Cocos Island (Costa Rica) are thought of as originating at Cocos, because currents are only known to flow south from Cocos (Rosenblatt and Walker, 1961), and no direct surface currents are known to flow from the Galapagos to Cocos Island (Wooster and Hedgpeth, 1966). The seasonally cold Peru current can select against establishment of some tropical elements in the Galapagos (James, 1984), but most species there are from the tropical mainland (Tables 1, 2, Fig. 1). PANAMIC-PERUVIANTRANSITIONZoNE. Most of the tropical elements do not range south of 4°S (Figs. 1-3; 50S for fishes, Rosenblatt, 1967). Drastic changes in the oceanographic regimes begin to take place in this region (3-6°S; Abbott, 1966; Dolan et a1., 1972; Semenov and Berman, 1977; Fleminger, pers. comm., 1985), which also limit the northern extent of Peruvian species. A seasonal "transgression" (transition) zone exists between 4-6°S (Semenov and Berman, 1977), which apparently coincides with the Panamic-Peruvian tran- sition zone (Fig. 2). As already noted, Pol!icipes elegans seems to be a quasi- amphitropical transition zone endemic barnacle (Fig. 1, Group III), since it is known to be abundant only in the Mexican-Californian and Panamic-Peruvian Transition Zones. A species of the ostracod family Cypridinidae (Fig. 3, #87) has only been reported from this transition zone (Springer, 1982), and is considered a transition zone endemic. An undescribed species of Poecilasma (Poecilasma- tidae; Newman, pers. comm., 1985), collected at Callao (Peru, 12°S)may be an endemic of the Peruvian biota, since neither it nor any other member of the genus is known to occur coastally in the entire eastem Pacific.

SUMMARY Provincial associations in the Tropical Eastern Pacific have been considered for barnacles, and a model is proposed for the provinces in this region (Fig. 5). The shores of the Peninsula of Baja California constitute two transitional regions, one on the west coast, the other inside the Gulf(Figs. 4, 5). It could also be thought of as a continuous transitional region (Fig. 4). These consist mostly of Mexican and Panamic species overlapping Californian ones, plus a few short-range endem- ics. The Mexican Province extends south to about 14°N where it overlaps with elements of the Panamic Province s. str. (Figs. 2, 5). Further south, the Panamic Provinces (s.1. and s. str.) overlap slightly with the warm-temperate Peruvian Province between 4-6°S. This region constitutes one of the sharpest transition zones in the Eastern Pacific (Fig. 2). The Galapagos fauna is considered to be a sub-province derived from mainland Panamic tropical elements. The Mexican (18-25°N outside the Gulf of California, and 22-32°N inside the Gulf) and the Panamic s. str. (4°S to 14°N) Provinces seem to be the centers of distribution for the Eastern Tropical Pacific. The Panamic s. str. has the greatest diversity (Figs. 1, 2). The Gulf of Panama is known to be rich in short-ranging 420 BULLETIN OF MARINE SCIENCE, VOL. 46, NO.2, 1990 endemic molluscs (Keen, 1971) and barnacles (Laguna, 1985), and may be the heart of the center of distribution for the barnacles of the Tropical Eastern Pacific.

ACKNOWLEDGMENTS

I thank W. A. Newman (Scripps Institution of Oceanography) for access to his barnacle collection, for helpful discussions, encouragement, and for critically reviewing the manuscript. This work was supported by the Tinker Foundation, a Grant from Exxon Corporation (Smithsonian Tropical Research Institute, Panama), supplemented by a scholarship from the Instituto Para la Formacion y Aprove- chamiento de Recursos Humanos (Panama) and by a Grant from the Fundacion Filantropica Fidanque (Stanley Fidanque and Federico Humbert; Panama), Thanks are due to Mrs. Elinor Robson (Fundacion de Ciencias Marinas, Panama) for helping obtain additional funds in Panama, and moral support. Research was performed at the Scripps Institution of Oceanography.

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DATEACCEPTED: September 13, 1988.

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