Phuket Marine Biological Center Special Publication no. 16 (1996): 215-219 215 • DISTRIBUTION AND ABUNDANCE OF MOLLUSCAN CRYPTOFAUNA FROM KARAICHALLI ISLAND (GULF OF MANNAR), SOUTHEASTERN COAST OF INDIA By R. Jeyabaskaran, D. Asir Ramesh & A. L. Paul Pandian Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai -608502, India ABSTRACT Replicate samples of live coral, dead massive coral, dead branching coral, and live & dead coral were studied. The surface area, volume, percentage cover, biomass and percentage available living space were determined for molluscan cryptofauna in each habitat. The gastropods Pyrene versicolor, Drupa sp. and Cerithium sp. were common in branching corals. The bivalves Saccostrea cllecullata, Area sp., Isognomon sp., Pinctada sp. and Lithophaga sp. were common in dead parts of ramose corals. Mytilids were rare in living parts of ramose corals. Pyrene sp., Drupa sp., Cerithium sp. and Lambis sp. were found crawling on the surface of the massive corals . • INTRODUCTION Cryptofauna refers to the fauna living in coral substrates and certain fauna living on th e surface of the substrates (PeyrotClausade 1974). However, the term epifauna is also used for animals living on surfaces. Cryptofauna can be divided into two components: the 'true borers' and the 'opportunistic' species. The 'opportunistic species' cannot bore. They utilize cracks, crevices, or live at the bases of long coral branches where they are completely hidden. Most of the bivalves belong to the boring cryptofauna and the gastropods belong to opportunistic cryptofauna (Richard 1973). There is no clear distinction between opportunistic cryptofauna and epifauna. But we use the term cryptofauna in accordance with Richard (1973). • Habitat structure is an ecological topic in its own right, and should not be treated simply as a routine component of all systems (McCoy et al. 1991). Qualitative and quantitative work has shown that coral reef cryptofauna is diverse and abundant (Ebbs 1966; Reish 1968; McCloskey 1970; Grassle 1973; Kohn & Lloyd 1973; Hutchings et ai., 1992). Several studies have been made on the molluscs associated with corals in other reefs (Tailor 1971; Patton 1975; Hadfield 1976; Morton 1984). The aim of this study is to document the distribution and abundance of molluscan cryptofauna from Karaichalli Island of Gulf of Mannar, southeastern coast ofIndia. MATERIALS AND METHODS The study area is shown in Fig. 1. Replicate coral samples were collected during December 1994 at the southern tip of Karaichalli Island (8°57'N; 78°14'E) in the Gulf of Mannar, 18 km northeast of Tuticorin, southeastern coast ofIndia. Extensive coral reefs occur only at depths from 1-6 m at the northern and southern tips of this island. The coral reef is composed oflarge boulders with intermittent sandy spaces. Every year during the southw.est monsoon (April to October) several corals die due to the sedimentation. During that season, the branching corals are subjected to considerable damage by the mechanical force of high waves. Tropical Marine Mollusc Programme (TMMP) 216 colony internal space (Tsuehiya & Yonaha 1992). The corals wer e finally broken into small pieces to remove the associated molluscs. They were pr eserved in 10 % formalin for id~ntification and biomass measurements . Other cryptofaunal communities such as sponges, polych aet es, crustaceans, sipunculans and ascidians were not enumerated. 78"14' .t·/'· Karicha ll i Island .' ~ The surface area of the sample was determined by coatin g all surfaces of block, except the cut surface, with several layers of liquid latex until a coat of latex was built up. When dry, t he latex was peeled off a nd the surface area measured with a planimeter (Hutchings & Weate 1977). Figure 1. Study ar ea. The dotted pattern RESULTS AND DISCUSSION indicates reef areas. The habitats were classified into the four categories:. live coral , dead massive coral, dead branching coral, and corals with live and dead parts . Each colony was wrapped in a thin plastic sheet to determine the total colony displacement volume. Associated macrobenthic animals were removed from the coral colony after breaking with a hammer and chisel. The volume of coral pieces was measured (colony volume). Total colony displacement volume minus colony volume is an in dex of The density of cryptofauna molluscs in different habitats in relation to surface area, volume, weight and internal space are shown in Table 1. The list of molluscs collected from different habitats with theirrelative abundance are shown in Table 2. The percentage of molluscs in dead branched coral was higher t h an in the live branched coral. Dead massive coral harboured more molluscs than the live massive coraL The coral with live and dead parts had a higher percentage of molluscs than live coral. Table 1. Density of cryptofauna molluscs in different habitats. Habitst Live Coral a . Montipora digitata b. Porites solida Dead br anched coral Acropora surculata Total wet weight (g) Total volume (cc) Internal space (ee) area (em') Weight of molluscs (%) 720 610 318 212 76 21 268 174 2.58 0.91 648 237 82 182 3.40 564 196 48 169 . 1.62 570 640 260 223 62 41 154 172 2.72 1.08 Surface Dead Massive Coral Fauites uirens Live & Dead Coral 8. Pocillopora damicornis b. Favia pal/ida .' Phuket Marine Biological Center Special Publication n o. 16 (1996): 215-219 217 Table 2. Moll uscs collected from different habitats together with their relative abundance. C.L. D. P.~ , Coral with live and dead parts; B ~ Branched; M~Massive. Name of the species Live coral B M • GASTROPODS Dead coral B M • Scutus unguis Trochus radiatus T. stellatus T. tentorium Turbo intercostalis Nerita albicilla N. polita Nodilittorina pyramidalis Planaxis sulcatus • • • • • • • Planispira {allo,ciosa • • • • • '. • * • • • • • * • • Lambis lambis Cypraea caputserpentis Mure:c uirgineus • * • Cerithium obeliscus C. citrinum C. SCQ bridum Drupa tuberculata D. margarUicola Pyrene versicolor P. zebra • • • C.L.D.P. B M • • • • • • • • * • • * • • • * • • • • • • • • BIVALVES • Barbatia {uscn Area symmetrica Lithophaga gracilis L. leuigata L. nigra L. stramineus I sognomon isognomum Pinctada anomoides P. margaritifera Saccostrea cuccullata • • • • • • Venerupis macrophylla Petricola diuergens • P. lithophaga Gastrochaena gigantea G. im.pressa Pholadidea cheveyi Parapholas quadritozonata • • • • • • * * • • • • • • • • • • • • * • • • • • • • • • • • • • • • • • • • 218 Tropical Marine Mollusc Programme (TMMP) • The nature of the bottom, wave action, exposure, temperature, availability of suitable food and behavioural aspects of larvae and adults are involved in determining the distribution and abundance of cryptofauna (Hutchings & Weate 1977). Roughgarden (1975) proposed three conditions n ecessary for a symbiotic relationship to evolve: i) the host should be easy to find . ii) the host should survive well with the symbiont. iii) the host should provide substantial benefit to the guest . In this case, corals provide food and shelter for the molluscs . Due to higher nutrient availability and plankton productivity, molluscs appeared more prominent on the bases and undersides of corals. Branching corals are better for byssus secreting forms, and massive corals are mm·e suitable for cemented or boring bivalves. Large dead molluscs could act as a substrate for coral settlement . However, the role of mollusc cryptofauna in different habitats of coral reefs is not fully understood . ACKNOWLEDGEMENTS The authors thank Mr. N. Jesu Raja, SCUBA diver, for collecting the organisms. REFERENCES Ebbs, N. K. 1966. The coral-inhabiting polychaetes ofthe Northern Florida reef tract. Part 1. 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