The influence of physicochemical parameters on the diversity and abundance of copepod species in Eruvbi Stream, Benin City, Edo State, Nigeria

Abstract

Zooplankton, particularly copepods, serve as crucial indicators of aquatic ecosystem health due to their sensitivity to environmental changes. This study examined the influence of physicochemical parameters on copepod community structure in Eruvbi Stream, a tributary of Ikpoba River, Benin City, Nigeria. Water and zooplankton samples were collected from three stations (upstream, midstream, and downstream) between March and June 2023. Physicochemical analysis revealed significant variations (p<0.05) in air and water temperature, electrical conductivity (EC), total suspended solids (TSS), turbidity, sulphate, alkalinity, hardness, and chemical oxygen demand (COD), while other parameters showed no significant difference (p>0.05). A total of 61 copepod individuals from two orders, Cyclopoidae and Calanoidae, comprising seven species, were recorded. Thermocyclops crassus (26.23%) and Mesocyclops salinus (22.95%) were the most abundant, while Eurytemora affinis (1.64%) was the lowest. The ecological diversity, using Shannon-Wiener and Margalef’s indices, showed the highest density in Station 1 and the lowest in Station 2. Similarity tests using the Jaccard and Bray-Curtis indices showed some level of similarity across the three stations. All correlation analyses showed significance at a 95% confidence level (r ≈ 0.67). Correlation analysis showed a strong positive relationship between EC and alkalinity (r ≈ 0.95) and between biochemical oxygen demand (BOD₅) and COD (r ≈ 0.89). Canonical Correspondence Analysis (CCA) revealed that copepod abundance was positively influenced by temperature and depth but negatively affected by high conductivity and TSS. These findings highlight the impact of physicochemical parameters on copepod distribution and underscore the influence of human activities on aquatic biodiversity.