TAXONOMIC STRUCTURE OF THE BENTHIC MACROINVERTEBRATE FAUNA FROM A TROPICAL RAINFOREST RIVER IN SOUTHERN NIGERIA.

The taxonomic structure of aquatic ecosystems in Nigeria is under threat from the over-exploitation of its natural resources and the discharge of pollutants into it. The impact of anthropogenic activities within the watershed of Owan River on the benthic macroinvertebrate community structure was investigated. A total of five hundred and thirteen individuals (513), comprising of of eleven (11) species distributed in nine (9) families, seven (7) order and two (2) phyla were recorded during the study. The distribution of benthic macro-invertebrate was in the order Station 1 > Station 2 > Station 3 000> Station 5 > Station 6 > Station 4, with species abundance highest in Station 1 (159) and lowest at Station 4 (28), while diversity was highest in stations 3 and 6. The observed phyla were Arthropoda (8 species) and Mollusca (3 species) from the orders Basommatophora, Caenogastropoda, Decapoda, Diptera, Neotaenioglosa, Odonata and Trichoptera. The species Tympanotonus fuscatus (62.18%) of the phylum Mollusca was the most dominant, while the species Caridina africana (1.56%), Clinotanypus sp (1.36%) and Corynoneura sp (1.56%) of the phylum Arthropoda were rare. Diversity indices of Dominance Index (0.27 to 0.48), Evenness index (0.47 to 0.73) and Margalef index (0.79 to 1.50) showed that the diversity of the species was generally low. The dominance of T. fuscatus and M. tuberculatus is an indication of deteriorating water quality from pollution. There is need to forestall further decline in water quality to enhance the restoration and productivity of the aquatic ecosystem.