Biodiversity and structure of the suprabenthic assemblages from South Shetland Islands and Bransfield Strait, Southern Ocean

During the austral summer 1995, suprabenthic samplings were carried out at 24 stations (depth range 45-649 m) located around Livingston Island, within the caldera of Deception Island and in the Bransfield Strait. At each station, the near-bottom motile fauna was simultaneously collected with a multinet Macer-GIROQ sled in three water layers above the bottom. This study presents original data on the occurrence, diversity, vertical distribution and abundance of suprabenthic taxa in this near-bottom environment. The most speciose taxa were amphipods (at least 140 spp.), followed by isopods (66 spp.), pycnogonids (31 spp.) and mysids (19 spp.). Total abundances ranged between 31 ind./100 m(2) (Bransfield Strait, 361 m depth) and 6817 ind./100 m(2) (South Livingston Island, 163 m depth). According to stations, the groups numerically dominant and more frequent were amphipods (17 stations) or mysids (seven stations). Four suprabenthic assemblages were discriminated in the study area, apparently more structured by the degree of shelter-exposure and development of sessile epifauna than by water depth or sediment features.