Effects of ecosystem disturbance on zoobenthos of a river in Western Nigeria

Abstract

An investigation on the macrobenthic invertebrates of Gbaagbaa River was carried out from February to June 2005 from three stations to assess the environmental impacts associated with the macrobenthic fauna community. Water chemistry samples were collected on monthly basis while, benthic macrofauna was sampled fortnightly by using the Ekman Grab for shallow water bodies. The estimated values for pH, conductivity, dissolved oxygen and biological oxygen demand were within the range of most tropical freshwater bodies. A total of 39 taxa (species) from 35 genera comprising 2,739 individuals were collected from the study area. The dominant groups were Diptera, Odonata, Ephemeroptera and Decapoda while Hempitera, Lepidotera and Amphibia (tadpoles) constituted the rare groups. Taxa richness was highest at Station 3 (5.37) and least at Station 2 (4.42). While, evenness values ranged from 0.77 at Station 2 to 0.89 at Station 3 and relative abundance was least (24.72%) at Station 2 and highest (49.29%) at Station 3. Fauna occurrences in the three stations were significantly similar as revealed by soreness quotient. Positive significant correlations were established between Diptera and all the other groups (P<0.05) except for between Trichoptera and Lepidoptera. Low number of taxa and individuals were recorded for the study period.

Keywords: Benthic invertebrates, species composition, abundance, ecosystem, Gbaagbaa River