Abstract
The benthic meiofauna of the two river systems, the Swartkops and Gamtoos, in the Eastern Cape of South Africa has been studied extensively. Various biological indices and statistical packages were used to assess the biological status of the nematode communities in the two rivers. Nematode identification was done to the genus level. Various environmental conditions, including, concentrations of Zn, Mn, Fe, Cu and Pb, organic carbon and chlorophyll-a in the sediments, were investigated in relation to the nematode density, diversity and community structure. The results of the studies indicate that higher concentrations of heavy metals had a negative impact on the nematode density, diversity and community structure. Nematode genera such as Rhabditis, Monhystera and Theristus were found to be tolerant to pollution or indicators of pollution. The Swartkops River estuary was found to be polluted more severely than the Gamtoos. It was realised that some nematode genera such as Viscosia can establish themselves along the river estuaries, irrespective of the salinity gradient. The quantitative effects of individual metals on the structure of meiobenthic communities could not be differentiated from one another. Similarly, the effects of metals and organic carbon on the structuring of the nematode communities could not be distinguished from one another. It is suggested that more studies of this kind be carried out along the coast of Africa to establish the potential indicator value of nematodes on the African continent.
Highlights
It has been observed that estuaries are among the most productive ecosystems in the world and are very vulnerable to anthropogenic activities
The percentage organic carbon content of the sediment at the eight sites in the two estuaries is shown in Table 1, and indicates that the Swartkops River estuary is relatively enriched with organic matter
This study has revealed that it is difficult to differentiate between the quantitative effects of individual metals (e.g. Cu, Zn, Fe, Pb), on the structure of nematode communities
Summary
It has been observed that estuaries are among the most productive ecosystems in the world and are very vulnerable to anthropogenic activities. Many researchers have used meiofauna and nematodes in particular as indicators of pollution in different environments. A similar study [10] that applied toxicity tests on the whole nematode community from Restronguet Creek, a severely contaminated estuary, showed that nematodes are more resistant to copper than those from an adjacent, less contaminated estuary. This is a result of an increase in the abundance of Cu resistant species, the evolution of enhanced Cu tolerance in some species and the probable exclusion of more sensitive species. This makes it possible to use the occurrence of metal tolerant individuals to map the ecological impact of contamination by these metals
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