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SUMMARY
A preliminary investigation of the macrobenthic invertebrates of the sediments of Lake Cubhu, a freshwater coastal lake near Richards Bay was conducted on a quarterly basis during 1987. The most important factor which determined the abundance and distribution of each species appeared to be the type of substratum. Analysis of the surface sediments enabled the lake bed to be separated into three main substratum categories; sand, mud and detritus. The highest densities of benthic animals occurred in sandy substrata while areas with detritus supported a greater number of species. In terms of animal density, muddy substrata were the least productive. Fourteen taxa of macroinvertebrate were recorded in the lake. Of these, only eight were identified as far as species. Two species of relict estuarine amphipods, Grandidierella lignorum and Corophium triaenonyx were numerically dominant in the benthos. The former was particularly abundant in sandy substrata where it reached densities of 12 500 m−2. However, the proportional contribution of G. lignorwn to the total density of animals decreased markedly in detrital substrata while that of C. triaenonyx remained constant. This suggests that of the two species, C. triaenonyx has a greater adaptability to varying habitats. Reasons for the dominance of these two relict estuarine amphipod species, G. lignorum and C. triaenonyx, in freshwater Lake Cubhu are discussed. Of the truly freshwater component, the major contributor to the macrobenthos was the bivalve Corbicula africana which was most abundant in sandy areas where it reached densities of 1 169 m−2.
