Species diversity and assemblages of macrobenthic Mollusca from the South Shetland Islands and Bransfield Strait (Antarctica)

During the research program BENTART 95, carried out from 16 January to 4 February 1995 on board RV Hesperides, a semi-quantitative Agassiz trawl and quantitative Van-Veen grabs were used at 31 subtidal stations between 40 and 850 m depth around Livingston Island, at Deception Island and in the Bransfield Strait. These data were used to search for and analyse the malacological assemblages. Among the molluscs sampled were 1,786 individuals belonging to 70 species of Solenogastres, Gastropoda Prosobranchia and Opisthobranchia, Scaphopoda and Bivalvia. The values of Shannon-Wiener diversity index ranged between 0.00 (one specimen) and 3.95, while Pielou's evenness index varied between 0.0 and 1.00. The bivalve Thyasira cf. dearborni was the most abundant species (227 specimens). Species richness varied from 1 to 19 species. Diversity showed great variations at different stations. The clustering analysis applying the Bray Curtis coefficient allowed species classification according to constancy and fidelity, and distinguished four groups of stations: one that gathers clearly the stations of the inner bay of Deception Island, excepting station 1, and the other three fitting the remaining stations, located north and south of Livingston Island and in the Bransfield Strait, and correlated with environmental factors (granulometric composition, organic matter and carbonates).