Plankton and macro-benthic invertebrate diversity of Apodu Reservoir in Malete, Nigeria

The present study investigated the physicochemical, phyto- and zoo-plankton, macro-invertebrate composition and abundance in Apodu Reservoir in Malete, Ilorin, Kwara state, Nigeria. Samples were collected twice a month in duplicate using standard techniques between February and July 2021. The physicochemical parameters of water: pH, electrical conductivity, water temperature and total dissolved solids were measured in situ using a portable water tester, and the other parameter were measured using standard methods. A sampling net with a mesh size of 0.5 mm were used for plankton collection while benthos were sampled using an Ekma grab sampler. The species richness and diversity were calculated using PAST 4.03 software. The result of the physicochemical parameters, phyto- and zoo-plankton and benthic macro-invertebrates showed significant differences between dry and rainy seasons. Nineteen species of phytoplankton and 13 species of zooplankton were identified in the reservoir. The Simpson index (1-D) values for dry and rainy seasons were 0.7654 and 0.8595, respectively, while the Margalef index values for dry and rainy seasons were 1.82 and 2.919, respectively. The study indicated that the reservoir water was slightly alkaline (pH 7.63 – 8.63) and had a low level of dissolved oxygen (4.9–5.8 mg/l). The occurrence of pollution-resistant phytoplankton species: Oscillatoria spp., Microcytis spp., and Microthamnion zooplankton species: Bosmina meridinalis, Keratella tropica, Branchionus calyciflorus and macro-invertebrates species: Namalycastis abiuma indicated the eutrophic status of the reservoir water indicating the reservoir is under anthropogenic pressure. Therefore, reservoir management activities such as protecting the reservoir areas and proper functioning of the reservoir to reduce, human activities are recommended.