Distribution of Macrobenthic Fauna of Soft Substrata in Swartkops Estuary, with Observations On the Effects of Floods

Abstract

The quantitative distribution of the macrofauna inhabiting soft substrata in the Swartkops estuary has been studied in relation to the prevailing abiotic and biotic factors. The most important factors limiting macrobenthic distribution appear to be substrate and competition between communities, while salinity plays only a small rôle. Four major communities have been recognized, each one dominating one reach of the estuary and a minor community dominating the silty heads of creeks. These communities are respectively a Callianassa community, an Upogebia community, a bivalve community and another Callianassa community as one proceeds from the mouth to the upper reaches. The creek community is dominated by four crustaceans and a goby. Biomass values have been recorded and related to the amounts of available food. The effects of floods on the fauna have also been monitored.