The effect of habitat structure and the interactions between four juvenile fishes and zooplankton-prey in a tropical estuary

Estuaries provide a variety of habitat types for fishes, where abundant food resources and protection from predators have been identified as important drivers of the high abundance of species that use these areas as nursery grounds. However, scientific consensus regarding the role of some habitats as nurseries remains limited. Here, we analyzed the trophic ecology of four juvenile fish species (Atherinella brasiliensis, Anchoa hepsetus, Rhinosardinia bahiensis, and Diapterus rhombeus) that occupy three habitats in a tropical estuary (mangrove fringes, seagrass beds, and mudflats), using samples collected during rainy and dry seasons. The aim of the present study was to investigate whether variations in the diet composition of juvenile fishes were mediated by changes in zooplankton prey availability in these estuarine habitats during the seasonal cycle (rainy/dry). The fish and zooplankton prey were caught at the same time. The analysis suggested that changes in the abundance of zooplankton prey items in estuarine habitats and seasons may have significant effects on fish diet. However, complex habitat structure did not drive predator-prey relationships. Mudflats are the main foraging sites for juvenile fishes in this tropical estuary, while fringe mangrove showed a weak influence on the abundance and diet of juvenile filter-feeders (R. bahiensis and A. hepsetus). The juvenile fish species were dependent on multiple habitats, and no species used only one habitat type exclusively. Understanding the dynamics of prey resources in different estuarine habitats is critical for their conservation, especially in those habitats that are uncommonly considered, such as mudflats.