Spatial and seasonal fish assemblage dynamics in a heavily urbanized estuary affected by interbasin water transference (Northeast, Brazil)

Estuarine ecosystems exhibit substantial spatiotemporal variation in their environmental conditions, resulting in a dynamic fish assemblage. However, anthropogenic alterations in hydrological flow and nutrient concentrations can potentially modify the spatial and temporal structuring of the fish community. This study aimed to elucidate how the characteristics of fish assemblages vary in space and time in an estuary (Cocó River, Ceará State, Northeast Brazil) that experiences significant impacts stemming from untreated domestic effluent discharge and water transfer from other hydrographic basins. The fish assemblage exhibited low total species richness alongside a high number and biomass of freshwater species, including non-natives. A stable spatial structure across seasons was discerned, implying diminished connectivity between estuarine zones. Changes in the trophic structure of the ecosystem could be inferred from variations in trophic composition among different zones. The findings presented herein demonstrate the alterations that interbasin water transfer may induce in estuarine fish assemblages, with potential ramifications for ecosystem functioning.