Unveiling demersal fauna diversity in South Africa’s east coast offshore habitats

Knowledge of deeper marine ecosystems is limited relative to that from coastal regions but is nevertheless important for broader decisionmaking purposes. Limited access to suitable vessels in KwaZulu-Natal Province (KZN) on the subtropical east coast of South Africa means that opportunities to sample offshore demersal macrofaunal communities from soft sediments is constrained. Trawl sampling of demersal fauna on the shelf and slope was conducted in 2010 in areas associated with nutrient sources to improve our understanding ecosystem processes. A total of 41 trawls were conducted along four transect focus areas (i.e. Durban Eddy, uThukela Mouth, Richards Bay South and Richards Bay North) in two seasons: 21 trawls in March (wet season) and 20 trawls in August (dry season). Overall, invertebrates contributed 40% by number and 30% by weight, and catches were considerably higher in the wet season than in the dry season. Catches were diverse, with 7 phyla, at least 15 classes, 15 orders, 110 families, 134 genera and 116 species represented. Arthropoda dominated by number, and Porifera by weight, with substantial contributions from Cnidaria, Mollusca and Echinodermata. The depth (ANOSIM R = 0.932) and focus area (R = 0.488), not season, were prominent and significant drivers of diversity patterns. Although considerable offshore biodiversity in KZN is yet to be described, this study reveals a marked contrast between the demersal fauna of this region and that of other South African marine areas.