How do Environmental Factors Influence Zooplankton Diversity in the Peri-Urban Amagba-Okoroma River?

Rivers are renowned for the provision of essential ecosystem services; and their presence in peri-urban and rural areas play and essential part in supporting their welfare and development. The zooplankton diversity in the Amagba-Okoroma River located in a peri-urban area in Benin City, Nigeria was investigated to provide foundational data on the ecological state of the river. Zooplankton and water samples were collected and analysed seasonally, three times each in the month of March and July, 2023 from three stations using standard methods. Principal component analysis shows that out of the 20 environmental factors, seven significantly influenced the zooplankton community. Three zooplankton groups comprising a total 360 individuals from 23 taxa were recorded. Of these, 11 species of rotifers, 8 cladocerans and 4 copepods were the predominant species found. Ecological indices suggested that species diversity were heterogeneous in favour of stations 2 and 1, as opposed to 3 being the least diverse. The zooplankton population was numerically higher in the dry season than in the wet season, albeit statistically similar. Cluster analysis showed that the organisms were grouped by stations into 2 clusters. Canonical correspondence analysis demonstrated a robust correlation between zooplankton and the physico-chemical parameters of the peri-urban river, with species such as Diaphanosoma sarsi and Euryalona orientalis being responsive, suggesting positive connection with BOD5 and DO. Whereas species like Moina micrura, Mesocyclops aspericornis and Mesocyclops salinus were tolerant. Generally, the studies show that the zooplankton diversity is influence by the physico-chemical factor of the river, and hence can be used as a biomonitoring tool for water quality.