MARCOINVERTEBRATES FUNCTIONAL FEEDING GROUP IN ORHIONMWON AND IKHIOGBE RIVERS

ABSTRACT

Declines in macroinvertebrate biodiversity pose a significant threat to key ecosystem services. Current analyses of biodiversity often focus on taxonomic diversity which does not account for the functional role of a species. Therefore, data on the functional composition of macroinvertebrates in tropical rivers are needed to develop models of ecosystem functioning and to assess anthropogenic effects on ecological condition. The macroinvertebrate functional feeding structure of Orhionmwom and Ikhiogbe Rivers, Edo state Nigeria was examined, and macroinvertebrate samples were collected from four ecologically distinct stations monthly for both wet and dry season from August 2021 to January 2022. Taxa recorded were allocated to functional feeding groups (FFG) using published literature and examination of gut contents. Clearly, the spatial distribution of most species reflected morphological and trophic suitability to particular environmental conditions. The results revealed that collector-gatherers (Baetis sp., Chironomus sp. and Oligochaetes) dominated the functional feeding groups, followed by predators (odonata, coleoptera, and diptera species), followed by Shredders (Caridina africana and Formicidae) at stations I, II, III and IV. Scrapers and collector filterers were only sporadically present mostly in stations I, III and IV respectively. The scantiness of shredders at all stations examined could be explained by the enhanced microbial activity replacing shredder activity at high temperatures common in most tropical streams. Twelve indices (comprising FFG, taxonomic, and diversity) used in ecological assessment were used to discriminate between each station. Our result suggests that the abundance and relative proportion of the functional feeding groups showed variation across the study sites, and can be used to assess and understand the role of aquatic macroinvertebrates in river ecosystems.