Zooplanktonic Community Assessment over Space and Time: A biomonitoring Tool in an Artificial Lake

Aims: The prime objective of this study is to determine the taxonomic composition of the zooplankton fauna of Esa-Odo Reservoir in Osun State and determine the spatial (horizontal and vertical) and seasonal variations in the composition, distribution abundance, and community structure of the zooplankton community in the reservoir. Study design: sampling stations were selected horizontally and vertically to cover the entire zones of the reservoir. Planktonic samples were collected at two months intervals for two years. Methodology: Samples were collected from the depth using an improvised Meyer’s water sampler. Net and Total plankton were sampled by filtration and sedimentation methods. Planktonic samples were preserved as 5% formalin and 1% Lugol’s solution.  Measurement, enumeration, and scaled pictures of the recorded zooplankton were taken using a photomicrograph. The taxonomic composition of zooplankton biota was determined using identification keys. Data analysis was done using PAST Statistical Package. ANOVA was used to determine the spatio-temporal variations. Results: Fiftyty-three (53) pecies of total zooplankton recorded in this study belong to 4 groups:  Rotifera, Cladocera, Copepoda, and Insecta. Rotifera was the most represented group (61.21%). Horizontally, 24 species with the highest mean abundance characterized the lacustrine; while 12 species and 10 species were unique to the transition and riverine zones, respectively.  Vertically, most species had their mean abundance decreased from the surface to the bottom of the reservoir. A total of nine (9), two (2) and one (1) species were peculiar to the surface, bottom and mid-depth, respectively. Zooplankton organisms were most abundant during the dry season. Conclusion: Esa-Odo Reservoir comprised highly diversified zooplankton fauna with great potential to support rich aquatic community and fishery production. The reservoir can be classified as fairly clean based on the abundance of the rotifer group. However, the lake should be subjected to regular proper monitoring because of the presence of some pollution tolerant copepod species identified among the zooplankton fauna.