Are zooplankton useful indicators of ecological quality in Afrotropical ephemeral stream impacted by human activities?

Ephemeral river systems in Nigeria are under severe threat by increasing anthropogenic pollution. However, little is known about the ecological health of ephemeral rivers in Afrotropical regions, especially Nigeria. It is also unclear how zooplankton communities respond to anthropogenic stressors in ephemeral rivers in the African continent. In this study, we explored the responses of zooplankton to environmental indicators of human activities to assess the health of River Kafin Hausa, an ephemeral river system in north-western Nigeria. Our specific objectives were to explore the response patterns of zooplankton communities to anthropogenic pollution in the north-western ephemeral rivers and examine their potential use as reliable indicators for long-term monitoring of ephemeral systems impacted by different human activities. We collected zooplankton and physicochemical variables from three sites in five months, from January to February and April to June 2018. One-way ANOVA showed air temperature, water temperature, pH, salinity, BOD, phosphate and nitrate varied significantly (p < 0.05) between the sites across the 5 months. We recorded four zooplankton groups, namely Cladocera, Copepoda, Protozoa and Rotifera. The cluster analysis revealed that the organisms were grouped mainly by sites rather than by seasons. The multivariate canonical correspondence analysis (CCA) revealed a weak association between the zooplankton community assemblages and physicochemical variables. However, there were differential responses of zooplankton to physicochemical variables in the river system, with species such as Eurytemora affinis, Acartia tonse and Sinodiaptomus sarsi being sensitive, indicating positive associations with DO concentration. Conversely, species such as Macrothrix rosea and Bosmina longirostris were tolerant, demonstrating their usefulness as bioindicators of bad water quality as they associated positively with TDS, water depth, nitrates and salinity. Overall, the study revealed further insights into the responses of zooplankton communities to pollution, and their potential use as indicators organisms in ephemeral rivers.