Distribution and abundance of the macrobenthic fauna of the kariega estuary

The Kariega estuary is an open estuary which is about 18 km in length. The freshwater inflow into the estuary is very sporadic and consequently the water is often hypersaline at the head. Quantitative and qualitative sampling has been undertaken to describe the distribution and abundance of the macrobenthos along the estuary. Of the 107 species that have been recorded, 80% can be classified as euryhaline. One of the possible reasons for the high species diversity, when compared to other eastern Cape estuaries, is the growth of Zostera capensis along the entire length of the estuary. The major contributors to the macrobenthic biomass are the crustaceans, Cleistostoma edwardsii, C. algoense, Upogebia africana, Sesarma catenata and Uca urvillei and the bivalve Solen cylindraceus. The latter is particularly abundant in the middle reaches of the estuary where it can reach densities of 400 m-2. Its successful colonization is attributed to food availability and stable physical conditions within the estuary which in turn can be linked to the low freshwater input.