Molluscan assemblages from the shelf and upper continental slope off Guinea-Bissau (north-west Africa)

The diversity and distribution patterns of molluscs in waters off Guinea-Bissau were investigated alongside their relationships with abiotic factors. Samples were collected using commercial bottom trawls during Spanish Bissau-0810 and three FAO-CCLME expeditions carried out on shelf and continental slope areas, over a depth range of 20–1000 m. A total of 126 species of mollusc were identified (86 gastropods, 39 bivalves and 1 scaphopod). Xenophoridae and Muricidae were the most frequent families, and the gastropod Ponderiana digitata was the most frequent species. Maximum mollusc density occurred between 100 and 200 m depth, with the bivalve Neopycnodonte cochlear dominating. Average diversity by strata decreased with increasing depth, with the maximum in shallow waters (<50 m). Separation of the three main assemblages (continental shelf, upper slope and middle slope) was influenced by a combination of environmental factors including depth, bottom temperature, sediment type and carbonates.