Diversity and Structure of Zooplankton Communities in the Bagoé River in Northern Côte d’Ivoire, West Africa

Abstract

The Bagoé River, located in northern Côte d’Ivoire, plays a crucial role in the local economy, notably through its provision of water and fishery resources. However, it is currently under significant anthropogenic pressure, mainly due to illegal gold mining, which severely affects its ecological quality. This study was conducted at three stations along the Bagoé River to assess the composition of the zooplankton community of the river. Sampling, including physicochemical measurements and zooplankton collection using a 55 µm mesh plankton net, was performed monthly from January to June 2025. A total of 30 taxa were identified, distributed across four major groups: Rotifers (17 taxa), Copepods (4 taxa), Cladocerans (4 taxa), and other zooplanktonic organisms (5 taxa), belonging to 17 families. The community was largely dominated by Copepods, representing 68% of total density. The lowest taxonomic richness (9 taxa) and abundance (200 ind/m³) were recorded at station S3, which is impacted by illegal gold mining. Copepods (75–80% of total zooplankton density) dominated in the non-impacted stations, whereas Rotifers (20–31.30% of total abundance) were predominant at the gold mining site, indicating a degradation gradient associated with human activities. The variables most strongly associated with zooplankton distribution were current velocity, transparency, conductivity, depth, temperature, pH, and dissolved oxygen. The relative proportion of Copepods and Rotifers thus appears to be a reliable biological indicator of aquatic ecosystem quality.