Macro-invertebrate community of Ozomu Lake, Benin City, Nigeria

Abstract

Macrobenthic invertebrates in lakes are frequently used to evaluate the overall ecosystem health of an aquatic ecosystem and can live on all bottom types. The study was conducted along the stretch of Ozomu Lake in Edo state, between March and December 2013. It aimed at determining the macroinvertebrate community structure of the lake. Samples were collected from three micro habitats; surface water, allochthonous and bottom sediment using an Eckman grab and a D-frame net. Few drops of 100% formalin were added to samples collected and transported to the laboratory. Identification to the lowest possible taxonomic level was performed under light microscope. A total of thirty-eight (38) taxa which comprises of 2276 individuals were collected. Plesiopora accounted for 1.14%, Haplotaxida 3.29%, Cyclopoidea 0.57%, Odonata 9.62%, Ephemeroptera 13.32%, Hemiptera 20.12%, Coleoptera 9.62%, Trichoptera 0.70%, Diptera 30.71%, Araneida 8.40%, Prostigmata 2.33%, Mesogastropoda 0.18%. The family Baetidae (Ephemeroptera), Culicidae, Chironomidae (Diptera), Gerridae, Pleidae (Hemiptera), and Dytiscidae (Coleoptera) were the most abundant species. The diversity indices revealed that taxa richness was highest in station 1 and lowest in station 2. Shannon- Wiener and Evenness index were higher in stations 1 and 3 than station 2. The macro invertebrate fauna was abundant during the rainy season than the dry season because the volume of water in the lake was reduced during the dry season. The dipterans of Ozomu Lake preferred bottom sediment habitat, surface water habitat than allochthonous habitat. The highest number of macro-benthic invertebrate was recorded in stations1 and 3, where there was restriction of human activities. However, human activities disturb the community of macro-benthic invertebrates in this ecosystem.

Keyword: Allochtonous, Bottom sediment, Community, Macro-invertebrate, Ozomu Lake, Surface water