Large-scale spatial patterns within soft-bottom epibenthic invertebrate assemblages along the west coast of South Africa, based on the Nansen trawl survey

Abstract

Knowledge of benthic invertebrate biodiversity and distribution patterns over the continental shelf of South Africa is poor and this is hampering efforts to design a network of marine protected areas aimed at conserving regional benthic biota. We analysed invertebrate biodiversity patterns within the offshore benthos along the west coast of South Africa, and 103 species, representing 9 phyla and 16 classes, were collected. The mean abundance of the benthic epifauna was 62 ind. ha^–1 (SD 39), and biomass averaged 5 233 g ha^–1 (SD 193). Demospongiae, Malacostraca and Echinodermata were the dominant taxa. Mean abundance was greatest in the 200–299 m depth zone (114 ind. ha^–1, SD 13) and mean biomass greatest in the 100–199 m depth zone (27 314 g ha^–1, SD 6 666). Based on the benthic invertebrate samples collected, six faunal communities were identified using multivariate analysis. Depth was the major factor determining benthic distribution patterns. Earlier studies used physical features as proxies to identify assemblages, but this study found more than one community within the same depth range.