Physico-chemical parameters and cyanobacterial communities of the Ebrié lagoon (Côte d'Ivoire): application to the risk of efflorescence

Résumé

 Cyanobacteria blooms in aquatic ecosystems lead to adverse effects in the water through the production of a variety of toxins that pose risks to wildlife and human health. For better management, appropriate monitoring programs must be put in place in potential risk areas. In our study, we examined the physico-chemical and biological indicators involved in blooms in order to map some surface waters of the Ebrié lagoon. The sampling was conducted from May 2021 to March 2022, on the lagoon ecosystem of the coastal region ranging from the cities of Grand Bassam to Jacqueville via Abidjan. The physico-chemical parameters of the water were measured using a WTW model 3430 multi-parameter in eight stations (Azuretti, GrandBassam, Koumassi, Koumassi 05, Adiapodoumé, Bietry, Marcory and Jacqueville,). Sampling of taxa was done with a plankton net of 20 µm mesh size. A light microscope was used to observe the various samples taken. Documents from various authors have helped to identify the different taxa. The results of the observation of the morpho-anatomical criteria of the cyanobacteria collected allowed us to identify 13 taxa grouped into 8 genera. Among these taxa, 3 are attached to species recognized as potentially toxic (Microcystis aeruginosa, Oscillatoria sp, Anabaena sp). The physicochemical parameters contributed to making the environment favorable to the development of microalgae, particularly cyanobacteria. Our study has shown that the alert levels are not reached and that only vigilance levels are raised during the low water season. All of the surveyed sites would be potential risk areas.