Identifying and categorizing potential indicator macroinvertebrate taxa in a southern Nigerian reservoir using a multivariate approach

       Anthropogenic activities within and around freshwater ecosystems are serious threats to the structural and functional assemblages of aquatic biodiversity. In the present study, identification and categorization of the potentially sensitive and tolerant macroinvertebrate taxa in a southern Nigerian reservoir were assorted, using a multivariate approach. Macroinvertebrates and selected physicochemical variables were sampled monthly in four sites for a period of two years (January 2009 to December 2010). PCA performed classified Site 1 as less impacted, and Site 4 as heavily impacted. Elevated mean values of pollution indicating Physico-chemical variables such as BOD₅, phosphate, and TSS were recorded in Site 4, and an increased concentration of DO was recorded in Site 1. Diptera dominated the 28 taxa of macroinvertebrate that were recorded in the entire study period, noting that the absolute abundance of Diptera taxa was higher at Site 4. NMDS revealed Sites 1 and 2 to form cluster B portraying similarity in the assemblage structure of taxa recorded in both sites, and cluster A formed a mixture of macroinvertebrate taxa assemblages from all the sampled sites. CCA and further categorization analyses performed identified and classified Centroptilum spp. to be very sensitive to pollution, while Mytilus dubia was the only taxon that was identified and classified as very tolerant of pollution. Overall the study pointed out the usefulness of using a multivariate approach in identifying and classifying potential indicator taxa for effective monitoring and management of freshwater ecosystems most especially in Sub- Saharan Africa where studies of this kind are still scanty.