Physical factors regulating macrobenthic community structure on a South African estuarine flood-tidal delta

Multivariate techniques were used to identify environmental parameters affecting macrobenthic communities on the flood-tidal delta of the Nahoon Estuary and adjacent beach near East London on the south-east coast of South Africa. Water content of sediments, temperature and exposure were identified as important parameters regulating differences in community structure between high-shore and subtidal sites, and between beach sites of varying elevation. High organic content was important for similarity of communities at sites farthest from the mouth and for distinctness of these communities from the others. Sediment particle size, compactness and current velocity contributed to similar communities of channel sites and their variation from those of other sites, and to distinctness of the lowest beach site from higher beach sites. Sites in the mouth and in the middle of the flood-tidal delta, with similarities in community structure, had varying values for all the measured environmental variables and none of these parameters could explain why these sites had similar communities. In summary, no over-riding parameter was shown to dominate the abiotic driving forces at all sampling sites, and different variables were important for structuring communities at different sites.