Ecological assessment of physico-chemical factors influencing the diversity and abundance of cyanobacteria in lakes of Côte d’Ivoire (Kan, Koubi, Loka, and Tiebissou)

Cyanobacteria are photosynthetic microorganisms found in all aquatic ecosystems. Some species produce toxins, posing risks to human and animal health. In Côte d'Ivoire, information on the composition and dynamics of freshwater cyanobacterial communities remains limited. This study aims to assess the influence of physico-chemical parameters on alpha diversity, cyanobacterial abundance, and phytoplankton biomass, while comparing community responses to anthropogenic pressures (urban, agricultural, and aquaculture). Nine sampling campaigns conducted between March 2023 and May 2024 included in situ measurements (pH, temperature, and turbidity) and laboratory analyses of nutrients and chlorophyll-a. Cyanobacteria were identified microscopically and quantified using a Malassez chamber. A total of 19 genera were recorded. Highly impacted lakes were dominated by opportunistic taxa (Aphanocapsa, Pseudanabaena, and Microcystis), whereas the reference lake was characterized by genera with high ecological plasticity (Cylindrospermopsis and Anabaena). Cyanobacterial abundance was positively correlated with pH and temperature, chlorophyll-a with pH and turbidity, and alpha diversity declined with increasing turbidity. Multivariate analyses (GLM, RDA, and NMDS) confirmed a significant influence of environmental variables on community structure. These findings indicate that cyanobacterial dynamics are primarily driven by physicochemical conditions and the intensity of anthropogenic pressures, highlighting the need for targeted ecological monitoring to support sustainable freshwater management.