Phytoplankton Diversity and Eutrophication Indicators under Anthropogenic Pressure in the Azagny Canal, Côte d'Ivoire

Abstract

Background: The Azagny Canal is a major artificial waterway in southern Côte d'Ivoire, playing a crucial role in the region's water management and economy. It connects the Ebrié Lagoon to the Bandama River and, thus indirectly, to the Atlantic Ocean. However, this transitional ecosystem is under increasing anthropogenic pressure. Aims: This study aims to characterize the phytoplankton communities in the Azagny Canal to assess the impact of human activities and environmental gradients, thereby providing biological indicators and essential scientific data for the sustainable management of this ecological corridor. Methodology: Micro-algae were sampled using a 20 µm mesh plankton net from February to August 2022. The sampling combined physico-chemical and biological analyses across five stations. Results: A total of 90 taxa were identified, revealing a dominance of Chlorophyta (43%) and Heterokontophyta (24%), with a heterogeneous spatial distribution. Station ST5 exhibited the highest taxonomic richness (45 taxa). Multivariate analyses demonstrated that water temperature, transparency, dissolved oxygen, conductivity, salinity, and nutrient levels (nitrite, nitrate, phosphate, and ammonium) significantly shaped the phytoplankton assemblages. The abundance of Chlorophyta and the presence of indicator species for nutrient enrichment confirm an ongoing process of eutrophication. Conclusion: This study validates the use of phytoplankton as a diagnostic tool for water quality monitoring and highlights the urgent need for management measures to protect this vital ecological corridor