First data on the diversity and structure of aquatic communities in the peri-urban river « Blondai » at Anyama (South; Ivory Coast)

The aim of this study was to characterise the diversity and structure of aquatic communities in the « Blondai » River (Anyama) with a view to assessing its ecological status. Three representative points (upstream, middle and downstream) were set up for sampling. The physico-chemical parameters of the water were measured in situ and in the laboratory. Macroinvertebrates were collected using a Van Veen bucket and a dip net, while plankton was collected by filtering 30 litres of water using a plankton net. Macrophytes were inventoried by direct observation on the banks, and fish by experimental fishing and ethno-zoological surveys. Biological diversity was analysed using the Shannon-Weaver index, Piélou equitability index and canonical correspondence analysis. The water in the « Blondai » river is acidic, poorly mineralised and moderately oxygenated. The taxonomic inventory identified twenty-three species of phytoplankton (18 families, 14 orders), eight species of zooplankton (2 families, 2 orders), twenty-one species of macrophytes (14 families, 14 orders), twelve species of macroinvertebrates (11 families, 9 orders) and four species of fish (3 families, 3 orders). The order Cichliformes has proved to be the most diverse among fish. Chlorococcales, Euglenophytes and Euglenides dominate phytoplankton, Poales macrophytes, while Diptera (Chironomidae), Coleoptera and Basommatophores dominate macroinvertebrates. The Shannon index showed low to moderate diversity, reflecting an unbalanced community structure. The CCA revealed significant relationships between organisms and several physico-chemical variables: pH, total nitrogen and dissolved matter influence zooplankton; BOD₅, COD and temperature condition the distribution of macroinvertebrates; turbidity and dissolved oxygen determine that of macrophytes; and total phosphorus and conductivity structure phytoplankton communities. No significant correlation was observed for fish.