Rapid colonisation of artificial substrates by macroinvertebrates in a South African lentic environment

Abstract

Macroinvertebrate colonisation patterns on artificial substrates were investigated in a small reservoir in the Eastern Cape, South Africa. Semi-closed 1 000 cm3 polythene netting cages filled with either brick, gravel, shredded plastic, or equal proportions of these three materials, were suspended above the benthic substrate. Gravel was preferred by caenid mayflies and chironomids, plastic by odonates, and brick by potamonautid crabs. Colonisation rates were rapid, with half the substrate-specific asymptotic diversity and richness being attained within a week. Overall, taxon richness on the substrates was similar to that in samples collected with a sweep net, but diversity was almost half. Taxon richness was found to be highest on the gravel and brick substrates, and lowest on plastic. By contrast, macroinvertebrate communities on the plastic and mixed substrates were the most diverse and the most even. All substrates, with the exception of gravel, showed that the number of odonates was significantly positively correlated with the number of potential prey that included chironomid midges, caenid mayflies and caddisfly larvae. It is recommended that plastic be used to construct artificial substrates if a high macroinvertebrate diversity is required for monitoring purposes within lentic environments.