Impact of urbanization on aquatic insect assemblages in the coastal zone of Cameroon: the use of biotraits and indicator taxa to assess environmental pollution

Internationally, waterways within urban area are subject to broad-scale environmental pollution. In this study, we used in-stream aquatic insects as surrogates to measure the aquatic health of urban streams in the Douala township. We compared these assessments with samples collected from a suburb stream. Aquatic insects were sampled monthly over a 13-month period in ten urban sites and two forest sites. Measurements of the environmental variables were done simultaneously. Results revealed that urban streams are highly polluted and ecologically impaired. The classification of samples by the self-organized mapping analysis permitted to clearly separate urban and non-urban aquatic insect assemblages. Higher total taxa richness, higher values of diversity indices, and higher Ephemeroptera–Plecoptera–Trichoptera (EPT) scores were recorded in forest sites. Inversely, in urban streams, very low taxa richness was observed, with the proliferation of dipterans, and the absence of EPT taxa. The EPT, coleoptera, and hemiptera taxa, the functional feeding groups of shredders and predators, and the insect taxa relying on gills and plastron for breathing were good predictors of anthropogenic pollution. Indicator taxa and ecological functioning traits identified in this study could enhance the accuracy of water quality assessment methodologies and potentially enable predictive models for evaluating the human impact in stream ecosystems.