Macrobenthic mollusc assemblages and diversity in the West Antarctica from the South Shetland Islands to the Bellingshausen Sea

Although frequent studies have been made on the benthos assemblages living in the Southern Ocean, few studies have dealt with molluscan assemblages and ecology. During the research programmes BENTART carried out in austral summers of 2003 and 2006 in a study area including Low Island, West Antarctic Peninsula, Bellingshausen Sea and Peter I Island, 45 stations were sampled using quantitative box-corer, Agassiz trawl, epibenthic sledge and rock dredge, at depths of 53-3,304 m. These data were used to search and analyse the malacological assemblages. A total of 2,889 living specimens of molluscs belonging to 139 species of shelled Gastropoda, Bivalvia and Scaphopoda were recoded. Gastropods were the best-represented in species richness, but the bivalves accounted the major abundance and Cyamiocardium denticulatum (460 individuals) was the most abundant species. Species richness varied from 1 to 37 species and diversity showed great variations at different stations. Four groups of stations of low similarities and some differences in faunistic composition were observed: one that gathers the Antarctic Peninsula and Peter I Island, one that also includes the Low Island, and two composed by stations of Bellingshausen Sea.