Zooplankton functional traits as indicators of the ecological status of sectors IV and V of the Ébrié lagoon, Côte d'Ivoire

The present study aims to assess the ecological status of Sectors IV and V of the Ébrié Lagoon using zooplankton functional groups at five sampling stations located in these sectors. Zooplankton was sampled monthly over a one-year period in the Ébrié Lagoon using a plankton net with a 64-µm mesh size. Physicochemical parameters were measured using a multiparameter probe. Water samples for nutrient analysis were collected using a 2.5 L Niskin bottle. Nutrient concentrations were determined in the laboratory using a UV 2700 molecular absorption spectrophotometer. A total of 48 zooplankton species belonging to three taxonomic groups (rotifers, copepods, and cladocerans) were identified in the Ebrié Lagoon and classified into five functional groups (RF, RC, SCF, MCF, and MCC). The low spatial and seasonal variability of environmental parameters and functional group biomass suggests a relatively homogeneous ecological structure across the lagoon. Zooplankton functional group densities did not differ significantly between the rainy (45.11 ind. L⁻¹) and dry seasons (54.88 ind. L⁻¹). During the rainy season, the highest densities were observed for small-sized filter feeders (SCF) at Mopoyem (28.31 ind. L⁻¹), while during the dry season, maximum values were recorded for filter-feeding rotifers (RF) at Layo (17.3 ind. L⁻¹). Phosphate and nitrate concentrations were positively associated with RF and medium-sized carnivorous copepods and cladocerans (MCC), whereas SCF were mainly influenced by ammonium concentration and water depth. This functional approach improves understanding of trophic dynamics and ecosystem functioning in tropical lagoons and provides a valuable baseline for future ecological monitoring and management.