A quantitative study to assess standing biomasses of macrobenthos in soft substrata of the swartkops Estuary, South Africa

Abstract

Abstract Totals of 44 intertidal and 19 subtidal transects were surveyed in the soft substrata of the non-marshland areas of the Swartkops Estuary. The sampling method (quadrat, suction and spear) depended on the substratum and the dominant macrobenthic species. Sampling effectiveness was measured and the numbers and standing biomasses of the 10 most abundant species were estimated for the entire estuary. Approximately 78 percent of total macrofaunal standing biomass (75,4 × 103 kg ash-free dry mass) was intertidal and 22 per cent subtidal. The dominant species were the thalassinid prawns, Upogebia africana and Callianassa kraussi, which made up about 82 and 10 per cent of total biomass respectively. The former dominated the muddy intertidal regions of the lower reaches and the latter the inter- and subtidal regions of the mouth and upper reaches. Solen capensis and S. cylindraceus were the dominant bivalves, but made up only some 3 and 1 per cent of the total calculated standing biomass respectively. The importance of these benthic forms as a food source to birds and fish is discussed.