The zoobenthic fauna of the Nhlabane coastal lake system, KwaZulu-Natal, South Africa, 20 years after construction of a barrage

The zoobenthos of the Nhlabane coastal lake system in northern KwaZulu-Nata l was sampled quarterly during 1992 in order to study the zoobenthic fauna of the Nhlabane lake and estuary. The ecology of the system was changed in 1977 when a barrage was constructed across the upper end of the estuary. Ph ysico-chemical parameters revealed that the previously escuarine southern b asin of the lake had become completely fresh. The estuary remained closed d uring the study period due to a drought, the presence of the barrage and wa ter abstraction from the lake. Benthic composition of the lake was typical of a shallow subtropical coastal lake, comprising a dominant estuarine asso ciated crustacean component and a typical freshwater component characterise d by oligochaetes, insect larvae and molluscs. Benthic densities varied wit h sediment type: with highest densities in detrital mud. The benthic compos ition of the estuary, dominated by estuarine amphipods and polychaetes, dif fered from that of the lake. There was a marked seasonal change in the bent hic community in response to the low salinities in the estuary. Benthic spe cies richness in the estuary was low relative to other estuaries, with a di stinct dominance of a few numerically important taxa, indicating an unstabl e benthic community. Reduced freshwater discharge due to the barrage and th e drought was the cause of the estuary mouth remaining closed throughout th e study period.