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ABSTRACT
Zooplankton diversity of the Amagba-Okoroma River, Benin City, Edo state, Nigeria was investigated from March 2023 to July 2023. Three stations were studied from upstream to downstream associated with various anthropogenic activities. Water and zooplankton samples were collected and analysed seasonally from March to April 2023 (dry season) and June to July 2023 (rainy season) using standard methods. A total of twenty-three (23) taxa were identified comprising 10 species of rotifers, 9 cladocerans and 4 copepods in the following order of dominance: cladocera> rotifera> copepoda. A total zooplankton population of three hundred and sixty (360) individuals was recorded during the study period. Cladocera and rotifera represented the predominant species (making up 47% and 31% of the total zooplankton community respectively) followed by copepoda (22%). The dominant cladocera species were Diaphanosoma sarsi and Euryalona orientalis, the different rotifera species identified were represented by just a few individuals, and the dominant copepoda species were Mesocyclops aspericornis and Mesocyclops salinus representing 22.2% and 16.6% of the total zooplankton, respectively. The calculated diversity indices indicated that station 2 was the most diverse followed by station 1, while zooplankton species in station 3 was the least diverse. Species number and density found in station one was fairly the same both in the dry and wet seasons. In station two, higher species number and density was seen in the dry season and in station three, species number was higher during the wet season. Correlation matrix revealed strong relationship between the physico-chemical parameters and zooplankton species. The results showed that water quality parameters exhibited great seasonal variation and controlled the structure of zooplankton community in the river.
