An assessment of macrobenthic invertebrates of the Ossiomo river, southern Nigeria
A study on macrobenthic invertebrates of the Ossiomo River was carried out in order to ascertain their composition, abundance, diversity and distribution in the river. This study which spanned a period of eight months (February to September, 2013) recorded a total of 65 species comprising 2,380 individuals shared among 3 phyla, 5 classes, 13 orders and 32 families in four designated stations along the river. Ephemeroptera and Diptera which constituted 37.98% and 37.73% respectively of the overall abundance of the macrobenthic invertebrates comprised the dominant taxa obtained. Representatives of the order Plesiopora which constituted 15.48% were accorded subdominant status while Decapoda, Hemiptera, Coleoptera, Odonata, Plecoptera and Trichoptera which individually constituted a value less than 5% were considered rare taxa. The abundance of the macrobenthic invertebrates across the stations showed a highly significant difference (P<0.01). The a posteriori Duncan Multiple Range comparisons revealed that the abundance of macrobenthic invertebrates at stations 1, 2 and 3 were significantly higher than that at station 4. Applying Jaccard and Bray Curtis similarity indices, no significant dissimilarity was recorded in the taxa composition among stations 1, 2 and 3. Species diversity as determine by Shannon-Wiener was generally high in all the stations, with the highest and least values in stations 4 and 1 respectively. Furthermore, these stations in turn recorded the highest and lowest values of evenness. The Ossiomo River depicts an ecological stable and robust ecosystem with minimal perturbation. The information provided in this study can serve as a reference for future studies in this river and also augment the scarce data available on the macrobenthic invertebrates in the Ossiomo River.
Key words - Macro-benthic invertebrates, Ossiomo River, composition, distribution, diversity