Depth-related changes to density, diversity and structure of benthic megafaunal assemblages in the Fimbul ice shelf region, Weddell Sea, Antarctica

The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha(-1) at 245 m to 8,895 ha(-1) at 510 m. While diversity was variable, with H ' ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages; a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas) but diversity was highest in intermediate areas (H ' = 2.35).