ATOLL RESEARCH BULLETIN NO. 368 CHAPTER 4 SPECIES COMPOSITION AND ABUNDANCE OF CORALS AND OTHER INVERTEBRATES ON THE REEFS OF THE SEYCHELLES ISLANDS BY N. I. SELIN, Y.Y. LATYPOV, A. N. MALYUTIN AND L. N. BOLSHAKOVA ISSUED BY NATIONAL MUSEUM OF NATURAL HISTORY SMITHSONIAN INSTITUTION WASHINGTON, D.C., U.S.A. June 1992 CHAPTER 4 SPECIES COMPOSLTION AND ABUNDANCE OF CORALS AND OTHER INVERTEBRATES ON THE REEFS OF THE SEYCHELLES ISLANDS N.I. eli in*, Y. Y. ~atypov*, A. N. ~alyut in* and L. N. ~olshakova** INTRODUCTION Coral reefs of the Seychelles Islands are not as well studied as those of Kenya, Madagascar and the Chagos Archipelago. Present knowledge is based on the collections of J. Stanley Gardiner made at the beginning of this century and on several later investigations performed on the reefs of Mahe Island and Aldabra Atoll (Gardiner 1936, Levi 1961, Lewis 1968, Rosen 1971,1979). This study deals with the distributional patterns of corals, molluscs, sponges and other common macrobenthic invertebrates of the Seychelles Islands coastal zones. METHODS AND MATE- The investigation of species composition and distributions of macroinvertebrates was conducted from the &lJ Akademik A, Nesmevanov (January - March 1989) down to a depth of 30 m using a combination of frame-quadrats and transects (Maragos and Jokiel 1976, Bouchon 1981) depending on the extent and morphology of a given reef. When a reef extended for hundreds of meters offshore (e.g., Desroches, Farquhar, St. Joseph and Cerf Islands), the distribution of organisms was analyzed at a number of widespread stations 200-500 m from each other. In the coastal zones of the granitic islands (Mahe, Praslin, La Digue) and also on Wetivy Island, a 100 m-transect marked at each meter was used. The animal populations and cover of corals were estimated using a 1.0 m2 frame divided into 100 equal squares. At most sites, subtidal stations continued on seaward from intertidal transects. Altogether, 33 profile sections (transects) in 13 localities were studied and the species composition of corals was determined for an additional 5 localities (Table I), while the species composition of sponges was determined for 12 sites (Table 2). Representative collections were archived at the USSR Academy of Sciences, Far East Branch, Vladivostok. RESULTS AND DISCUSSION An analysis of the species composition and distributional patterns of the floristic and faunistic populations of reefs of the Seychelles showed that major upper subtidal communities in all areas * Institute of Marine Biology, Far East Branch, USSR Academy of Sciences, Vladivostok, 690032, USSR ** Institute of Paleontology, USSR Academy of Sciences, Moscow, USSR studied are dominated by either scleractinian and alcyonarian corals, algae or seagrasses (for more detailed information on the flora of coastal waters of the Seychelles see Ch. 5, Gutnik et al., on alcyonarians - Ch. 3, Malyutin, of the present ARB issue). Abundances and the ratio of floristic and faunistic complexes substantially change from one island to another and even within one island area. This paper follows the descriptive scheme of reef classification for the Seychelles suggested by Stoddart (1984), who follows convention by dividing the reefs into three groups: fringing, platform and atoll reefs. Fringing reefs were most typically found on MahC Island. Near the northeast Point, at a distance of 120-130 m offshore, beds of the seagrass Thalassodendron ciliatum are replaced by a badly damaged reef built mainly by colonies of branched Stylophora pistillata, Pocillopora verrucosa and rarely by smaller colonies of massive Porites, which combined develop up to 3% cover of the calcareous or bedrock primary substrata. Considerable area here is covered with members of the order Corallimorpharia (subclass Hexacorallia). At a distance of 160-170 m offshore, the reef flat changes in slope inclining at about 25-30' down to 8-12 m in depth. Concomitantly, Scleractinia decrease in number and development (substratum area coverage no more than 1-2%); separate corallagenous blocks and landslips occur frequently. The gastropods Cypraea histrio, Conus distans, Lambis chiragra, the sea urchin Diadema as well as single individuals of the bivalve molluscs Tridacna mavima and Pinctada margaritifera can be found between scattered blocks. Farther seaward the sandy bottom is populated by massive, columnar and lamellar corals form at 12-15 m in depth. Goniastrea, Favia, Favites, Galaxea, Montipora and sponges of the genus Spirastrella are characteristic of this part of the reef. Single colonies of branched Acropora, which otherwise are well developed on reef slopes, are rare. Overall, coral cover reaches 80%. Similar compositions and vertical distributions of scleractinians were found near Anonim Island on the eastern coast of MahC Island; however the coral cover on the reef slope is about 40%, and Acropora, Pocillopora and Millepora are more abundant here. Granitic islands (Praslin, La Digue, MahC) have fringing reefs in their coastal zones, which are characterized by a well developed reef flat and rather steep slopes extending down to 13-23 m in depth. The shallowest protions of reef flats and reef fronts are dominated by calcareous algae and encrusting scleractinians which are replaced by Acropora and Pocillopora (covering about 20-40%) at 2-3 m in depth. Goniastrea and Favites are common on large boulders and rocks. At 12 m in depth, the reef slope forms a platform inhabited by massive Porites, Favia and foliaceous Pachyseris (covering up to 30%). Among the other invertebrates, the gastropods Lambis truncata (1 individualam- ), Chicoreus ramosus (l.m-2), Lambis crocata and smaller species are common. At a distance of 2-3 km from Praslin Island, at 20-30 m in depth, the reef platform is populated by colonies of branched Acropora and Turbinaria as well as. solitary Heteropsammia cochlea. At La Digue Island, coastal zone rock promontories 400-500 m offshore support isolated colonies of scleractinians, chiefly of the genera Pocillopora and Favia. In addition to corals, large settlements of the bivalve Lopha cristagalli (about 30.m.') and Pinctada margaritifera (up to 20.m-') are found. According to Stoddart's (1984) classification, reefs of the African Banks, as well as reefs of CCietivy, D'Arros, Cerf and Desroches, are indicative of platform reefs. Characteristic features of such reefs are a very slow increase in depth with increasing distance off shore, a long reef slope stretching over hundreds or even thousands meters, and extremely homogeneous compositions and distributions of organisms. The most salient features are given below, without describing each island in detail. Reefs of Cerf Island and African Banks extend over several kilometers offshore and are 40-60% covered by 40-90% the seagrass Thalassodendron ciliatum. Of the scleractinians, branched Stylophora pistillata, Porites cylindrica, massive Porites lutea and Favia spp. are of most frequent occurrence. There is no distinct zonation in the vertical distributional patterns of scleractinias in contrast to the typical fringing reefs of Mahe, Praslin and La Digue Islands. Coral colonies are not large (Porites lutea - < 20-30 cm in diameter), and total cover does not exceed 20%. Associated fauna includes the sea star Protoreaster lincki ( to 2 ~ m - ~ ) and the bivalve mollusc Pinctada margaritifera (about ~ . m ' ~ ) . In contrast to the reefs of the African Banks and Cerf Islands, the reef of the southeastern coast of D'Arros Island is smaller, with a more pronounced reef slope and scleractinian zonational pattern. Zonal alternation of monospecific populations is an interesting feature of this reef, the upper parts of which as a whole are similar in composition and development to the reefs described above. For example, the blue octocoral Helwpora coerulea is responsible for 100% cover at 17-25 m in depth. At 25-27 m (350-400 m from the reef front), separate juveniles of Acropora, Heliopora and the hydrocoral Millepora (about 50% cover) are replaced by monospecific populations of Millepora platyphyllEya, whereas at 27-30 m almost 100% of the substratum is occupied by Acropora. Porites and Favia become more common at greater depths where sand plains occur. On the reef as a whole, the gastropods Lambis truncata, Lambis arhnitica, Bursa bubo and the holothurian Telenota ananasare are of frequent occurrence, but they do not form large concentrations. The pattern of coral distribution in the coastal waters of Cdetivy Island represents an obvious case of local variability in vertical scleractinian distribution for the upper subtidal of the Seychelles. Abundant growths of the seagrass Thalassodendron ciliatum (90-100% cover) begin from the waterline along the northeastern coast of this island, and extend throughout the reef flat and gentle slope over 800-1000 m. With increased distance off shore, the abundance of T. ciliatum gradually decreases ( about 50% at 7 m in depth and about 10% at 17 m in depth) whereas scleractinians and alcyonarians increase somewhat. At a distance of 400-500 m, coral cover reaches 30-35%, consisting of small colonies of branched Acropora digitifera, Pocillopora verrucosa, Stylophora pistillata, Millepora platyphyffa, representatives of Platygyra, Galarea, Favia and several smaller species usually inhabiting sites that are free of seagrasses, but sometimes co-occurring with these macrophytes. Along the western coast of COetivy Island, Thalassodendron ciliatum occurs as a small belt between the coastline and the 1 m isobath. Immediately past the reef front, the scleractiian community begins with the dominant Stylophora pistillata densely covered with calcareous algae and Acropora digitifera (covering - 10-20%). Corals inhabit calcareous substrata together with the bivalves Tridacna crocea (1-10-m'2) and Cardina variegata (to 15-2~m-~). At 10-12 m in depth, the coral cover consists of mainly Heliopora coerulea and Acropora digitifera, similar to the rock promontories of Praslin and La Digue Islands. Deeper, patches ofAcropora and some colonies of Porites can be found. The third group of Seychelles reefs consists of the atolls Aldabra, Astove, Farquhar, Cosmoledo and St. Joseph. As a rule, atolls are characterized by platform reefs on the outer side and surround a shallow sandy lagoon. Considerable areas of the lagoons are often occupied by seagrasses, spreading into intertidal sites. Scleractinians are sparse here, with only small isolated colonies of Stylophora, Favia and Montipora. Cover does not exceed 5% in most areas. The associated fauna is re resented ? by the gastropods Monetaria moneta, Monetaria annulus (to 50.mm2), CLprea ti@ (0.2.m- ), and by the bivalves Pinna sp. and Codakia sp. The outer reef slopes facing the open sea, are often very extensive. Near the southeastern coast of St. Joseph Island, at distance of 1 km from shore (depth of about 25 m) a well-developed coral community is present with many scleractinias such as Pocillopora, Porites and Acropora (covering about 35%). Favia, Favites, Lobophyllia, Symphyllia and gorgoniak are of frequent occurrence. A similar situation is observed in the coastal waters of Farquhar and Cosmoledo Islands. Also, the reef slope at the eastern end of St. Joseph Atoll has an inclination of 45-70" (30-40 m from the shore and at 7 m in depth) and consists of the blue octocoral Hefwpora coerulea at its upper boundary (100% cover), and of massive and encrusting scleractinian species (Porites, Pachyseris) below 24 m where Helwpora cover is reduced to 20-40%. At 33 m, the reef changes to a sandy platform with isolated small colonies of Porites cylindrica and some other species. A slope of similar geomorphology is characteristic of the reef at the southwestern coast of Astove Atoll, where the reef at 6-8 m in depth is dominated by a monospecific cover of Porites cylindrica (100%) until it declines abruptly (inclination angle of 50-90") down to more than 40 m. Beginning from 17-18 m, coral cover decreases sharply and Porites cylindrica is replaced by small colonies of Platygyra and Favia. Deeper than 22 m, corals are not observed in this region and the reef slope is nearly 100% covered by algae. In summary, the Seychelles reefs, especially those of the northern granitic islands (MahC, Praslin, La Digue), show scleractinian compositions and distributional patterns that are very similar to most reefs of the Indo-West Pacific (for observations in Vietnam see Latypov, 1987). More or less distinct vertical zonational patterns are similar, dependent on succession of scleractinians from the same genera and life forms (e.g., branched and crustose Stylophora and Montipora on reef flats, branched Stylophora, Pocillopora and Acropora on reef slopes and massive, encrusting and isolated Porites, Pachyseris and Fungia at the bases of slopes and on platforms). The preliminary checklist of Scleractinia and Millepora corals of the Seychelles includes 51 genera. Earlier surveys of Aldabra and other granitic islands identified a total of 64 genera of hermatypic corals (Rosen 1971,1979, Pillai et al. 1973, Wijsman-Best et al. 1980, Sheppard 1987). Further study of the voucher collections will reduce this difference. In conclusion, it is important to note the absence of dense settlements of bivalve molluscs on Seychelles reefs. Bivalves play an important role in the function of coastal benthic communities of the tropical zones of other Indian and Pacific Ocean reefs. For example, Macna crocea on reefs in 1 the region of Townsville (Australia), forms populations with a density of up to 200.m- and is to a considerable degree responsible for the formation of micro atoll-like structures (Hamner and Jones 1976). In the coastal waters of Vietnam, this species along with other numerous and common Indo- Pacific molluscs, such as Arca ventricosa and Beguina semiorbiculata, seems to control important processes of bioerosion and biosedimentation. Only isolated individuals of these two species are also found on the Seychelles reefs. Bivalve molluscs are not as important for reef life in the Seychelles Islands as is the case on the Great Barrier Reef and in coastal zones of Vietnam, although their species diversity is comparatively high (Taylor 1968). The reasons for the differences in abundances of this invertebrate group in these regions is at present unclear. REFERENCES Bouchon, C. 1981. Quantitative study of the scleractinian coral communities of a fringing reef of Rdunion Island (Indian Ocean). Mar. Ecol. Prog. Ser. 4273-288. Gardiner, J.S. 1936. The reefs of the western Indian Ocean: I. Chagos Archipelago: 11. The Mascarene region. Trans. Linn. Soc. Lond. 2 (19):393-436. Hammer, W.M. and M.S. Jones. 1976. Distribution, burrowing, and growth rates of the clam Tridacna crocea of interior reef flats. Formation of structures resembling micro atolls. Oecologia 24207-227. Latypov, Y.Y. 1987. Scleractinian corals of South Vietnam. Biologia Moria (USSR) 512-19. Levi, C. 1%1. Les spongiaires de l'ile Aldabra. Res. Sci. Camp. Calypso 5(2):1-31. Lewis, M.S. 1968. The morphology of the fringing coral reefs along the east coast of Mahe, Seychelles. J. Geol. 76:140-153. Maragos, J.E. and P.L. Jokiel. 1976. Reef corals of Canton Atoll.2. Local distribution. An environmental survey of Canton Atoll lagoon. Nav. Undersea Res. (NCV)395:1-192. Pillai, C.S.G., P.J. Vine and G. Scheer. 1973. Bericht iiber einer Korallensammlung von den Seychellen. Zool. Jb. Syst. 100:451-465. Rosen, B.R. 1971. The distribution of reef coral genera in the Indian Ocean. Symp. Zool. Soc. Lond. 28:263-299. Rosen, B.R. 1979. Checklist of recent coral records for Aldabra (Indian Ocean). Atoll Res. Bull. 233:l-24. Sheppard, C.R.C. 1987. Coral species of the Indian Ocean and adjacent seas: a synonomized compiliation and some regional distributional patterns. Atoll Res. Bull. 307:l-32. Stoddart, D.R. 1984. Coral reefs of the Seychelles and adjacent regions. Biogeography and Ecology of the Seychelles Islands. Monogr. Biol. 5563-81. Taylor, J.D. 1968. Coral reefs and associated communities(main1y molluscan) around Mahe, Seychelles. Phil. Trans. R. Soc. Lond. 254:129-206. Wijsman-Best, M., G. Faure and M. Pichon. 1980. Contribution to the knowledge of the stony corals from the Seychelles and eastern Africa. Rev. Zool. Afr. 94:600-627. Table 1. Coral species from the coastal waters of the Seychelles Islands. M = MahC, P = Praslin, Co = Cdetivy, F = Farquhar and D = Desroches Species Island M P Co F D 1. Pocillopora damicomis (Linneus, 1758) 2. Pocillopora eydoui Milne Edwards & Haime, 1860 3. Pocillopora meandrina Dana, 1846 4. Pocillopora verrucosa (Ellis & Solander, 1786) 5. Pocillopora woodjonesi Vaughan, 1918 6. Seriatopora hystrir Dana, 1846 7. Slylophora pistillata Esper, 1797 8. Montipora foveolata (Dana, 1846) 9. Montipora millepora Crossland, 1952 10. Montipora spongodes Bernard, 1897 11. Montipora venosa (Ehrenberg, 1834) 12. Montipora verrucosa (Lamarck, 1816) 13. Montipora sp.1 14. Montipora sp.2 15. Anacropora sp. 16. Acropora aculeus (Dana, 1846) 17. Acropora anthocercis (Brook, 1893) 18. Acropora cerealis (Dana, 1846) 19. Acropora cytherea (Dana, 1846) 20. Acropora digitifera (Dana, 1846) 2 1. Acropora divancata (Dana, 1846) 22. Acropora fomosa (Dana, 1846) 23. Acropora grandis (Brook, 1892) 24. Acropora hyacinthus (Dana, 1846) 25. Acropora nasuta (Dana, 1846) 26. Acropora nobilis (Dana, 1846) 27. Acropora palifera (Lamarck, 1816) 28. Acropora poCystoma (Brook, 1891) 29. Acropora robusta (Dana, 1846) 30. Acropora venveyi Veron & Wallace, 1984 3 1. Acropora sp. 1 32. Acropora sp.2 33. Astreopora explanata Veron, 1985 34. Astreopora listen Bernard, 1896 35. Astreopora myrbphthalma (Lamarck, 1816) 36. Astreopora ocellata Bernard, 18% 37. Astreopora sp. 38. Pontes annae Crossland, 1952 39. Pontes cylindrica Dana, 1846 40. Pontes lobata Dana, 1846 41. Pontes lutea Edwards & Haime, 1860 42. Pontes murrayensis Vaughan, 1918 43. Porites nigrescens Dana, 1846 44. Porites stephensoni Crossland, 1952 45. Porites sp. Table 1. Continued. Species Island M P Co F D 46. Goniopora lobata Milne Edwards & Haime, 1860 47. Goniopora sp. 1 48. Goniopora sp.2 49. Alveopora sp. 50. Pseudosiderastrea tayamai Yabe & Sugiyama, 1935 5 1. Psammocora profundacella Gardiner, 1898 52. Psammocora superficialis Gardiner, 1898 53. Cosinaraea sp. 54. Pavona clavus (Dana, 1846) 55. Pavona minuta Wells, 1956 56. Pavona varians Verrill, 1864 57. Pavona sp. 58. Leptoseris mycetoseroides Wells, 1954 59. Gardineroserisplanulata (Dana, 1846) 60. Pachyseris sp. 61. Cycloseris cyclolites (Lamarck, 1801) 62. Diaseris sp. 63. Fungia danai Milne Edwards & Haime, 1851 64. Fungia granulosa Klunzinger, 1879 65. Fungia repanda Dana, 1846 66. Fungia scutaria Lamarck, 1801 67. Herpolitha limux Houttuyn, 1772 68. Herpolitha weberi Van Der Horst, 1921 69. Herpolitha sp. 70. Sandalolitha robusta Quelch, 1886 71. Galuxea astreata (Lamarck, 1816) 72. Echinophyllia aspera (Ellis & Solander, 1786) 73. Mycedium elephantotus (Pallas, 1766) 74. Pectinia lactuca (Pallas, 1766) 75. Acanthastrea bowerbanki Edwards & Haime, 1851 76. Acanthastrea echinata (Dana, 1846) 77. Acanthastrea hillae Wells, 1955 78. Acanthastrea sp.1 79. Lobophyllia sp. 80. Symphyllia aff. valenciennesii 81. Hydrophora microconos (Lamarck, 1816) 82. Caulastrea sp. 83. Favia maritima (Nemenzo, 1971) 84. Favia maxima Veron, Pichon & Wijsman-Best, 1977 85. Faviapallida (Dana, 1846) 86. Favia speciosa (Dana, 1846) 87. Favia stelligera (Dana, 1846) 88. Favia sp. 89. Favites abdita (Ellis & Solander, 1786) 90. Favites chinensis (Verrill, 1866) Table 1. Continued. Species Island M P Co F D 91. Favites fzemosa (Dana, 1846) M P 92. Favites sp. 93. Goniastrea aspera Verrill, 1905 P 94. Goniastrea edwardsi Chevalier, 1971 M P 95. Goniastrea pectinata (Hemprich & Ehrenberg, 1834) M P 96. Goniastrea retifonnis (Lamarck, 1816) M P 97. Plalygyra daedalea (Ellis & Solander, 1786) M 98. Plalygyra lamellina (Hemprich & Ehrenberg, 1834) 99. Plalygyra pini Chevalier, 1975 M 100. Plalygyra sinensis (Edwards & Haime, 1849) P 101. Leptoriaphlygia (Ellis & Solander, 1786) 102. Oulophyllia crispa (Lamarck, 1816) M 103. Montastrea annuligera (Edwards & Haime, 1849) P 104. Plesiastrea versipora (Lamarck, 1816) 105. Diploastrea heliopora (Lamarck, 1816) 106. Leptastrea bewickensis Veron, Pichon & Wijsman-Best, 1977 107. Leptastreapurpurea (Dana, 1846) M P 108. Leptastrea tramersa Klunzinger, 1879 M 109. Qphastrea serailia (Forskill, 1775) P 110. Quhastrea sp. M 1 1 1. Echinopora lamellosa (Esper, 1795) M 112. Moseleya latistellata Quelch, 1884 113. Turbinariafrondens (Dana, 1846) M P 114. Turbinaria mesenterina (Lamarck, 1816) M P 115. Turbinaria peltata (Esper, 1794) M P 116. Turbinaria renifonnis Bernard, 18% 117. Heteropsammia cochlea (Spengler, 1781) M P 118. Tubastraea micrantha (Hemprich & Ehrenberg, 1834) 119. Tubastraea sp. M 120. Siderastrea radians (Pallas, 1766) P 121. Tubipora musica Linaeus, 1758 122. Heliopora coerulea (Pallas, 1766) P 123. Milleporaplatyphylla Hemprich & Ehrenberg, 1834 M P Table 2. Sponges of the Seychelles Islands. i = intertidal and s = upper subtidal. M = Mahe, P = Praslin, Co = COetivy, F = Farquhar, D = Desroches, A = Aldabra, L = LaDigue, AB = African Banks, S = St. Joeseph, Pd = Providence, Cs = Cosmoledo and As = Astove. Island and Tidal Zone Genera C o C o F F A A D D P P M M L L A B A B S S P d P d C s C s AsAs i s i s i s i s i s i s i s i s i s i s i s i s Plakina Isops Co Stelleta Co Ecionemia Acanthobiaena Callipelta Scleritodenna Laxosuberites Co Spirastrella Diplastrel la Cliona Co Axinella CoCo Hemiasterella Euripon Micale CoCo Paracomulum Hymedesmia Spirorhabdia Co Pronax Clathria Microciona Acamus Trachyopsis Ciocalipta Co Prostylyssa Co Haliclona Co Adocia Co Taxadocia Co Reniera Petrosia Co Qsidea CoCo Phyllospongia Co Phakellia Co Coelodischela Hamactyoniaal Myil la Co