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Macro-Invertebrates Status of Oluwa River in Ondo State,Southwest, Nigeria

Olaniyan RF, Ugwumba AO and Ayoade AA

The macroinvertebrate fauna of Oluwa river, Ilaje Local Government Area, Ondo State, Nigeria were investigated for eighteen months (June 2014-November 2015) covering both the rainy and dry seasons. The major objective of the study was to provide baseline information on aspects of the biology (taxonomic composition, occurrence, distribution, and abundance) of the benthic macroinvertebrates. A total of six sampling stations were established to represent the various sections and regime of the river. Sediment samples were collected from each station at monthly intervals using an improvised Van-veen grab. Altogether a total of one hundred and sixty-two composite samples were collected and analyzed and assessed. The benthic macroinvertebrates made up of seventeen species belonging to three phyla; Arthropoda, Annelida, and Mollusca. They consisted of five classes: Crustacea, Gastropoda, Insecta, Oligochaeta, and Polychaeta. Altogether a total abundance of 2,264 individual macroinvertebrates species were collected from the bottom sediment. The gastropods were the most abundant and constituted 50% of the total benthic macro-invertebrates organisms encountered in Oluwa river. Pachymelanin aurita had the highest percentage (12.9%). The least amongst this group was Lanistes varicus (5.1%). Polychaeta accounted for 27% of the total benthic macroinvertebrates organisms in Oluwa river. Glycera capitata had the highest percentage (8.7%) abundance. The least amongst this group was G. convolute (4.1%). The class Insecta accounted for 12% of the benthic macro-invertebrates in Oluwa river, Chironomus larvae had the highest percentage (4.5%) abundance, while Chaoborus larvae accounted for the least value (3.1%). The class Crustacea accounted for 7% of the total benthic macro-invertebrates in Oluwa river. Amongst the groups, Nototropis swamidami accounted for the highest percentage (3.8%), while Iphinoe tripanosa accounted for the least value (3.4%) of the total composition. Oligochaetae accounted for 4% of the total benthic macro-invertebrates organism in Oluwa river. Ophinidomais serpentina was the only species recorded and accounted for 3.8% of the abundance.In conclusion, on the basis of benthic macroinvertebrate taxa composition and abundance, Oluwa river can be inferred to be rich in fauna composition and therefore fairly polluted.