Fish feeding interactions in a subtropical coastal system in the southwestern Atlantic

Feeding interactions, which determine the dynamics, productivity and stability of an ecosystem to a large extent, constitute fundamental knowledge for understanding the functionality of an ecosystem. Within an integrated working context, this study aimed to identify the major prey for the fish species of Araçá Bay through an analysis of stomach contents. Araçá Bay is a sheltered, low tide terrace that presents seasonal hydrodynamics, primary productivity and organism communities. A total of 1253 stomachs from 28 fish species were sampled in March 2013 and January 2014 (austral summer) and in June 2013 (austral winter). A hierarchical cluster analysis (Bray-Curtis similarity index) was performed on the matrix of the index of relative importance (IRI%) of the food items of 15 species collected in both seasons. Five and four major trophic groups were recorded for the summer and winter, respectively (SIMPROF). A two-way PERMANOVA test showed significant differences in the prey compositions among the trophic groups but not the seasons. The annual dendrogram showed four trophic groups: shrimp feeders (8 species), teleostean fish feeders (2 species), copepod feeders (2 species), and benthic invertebrate feeders (3 species). Seasonal species shifts among the trophic groups related to the seasonal recruitment of relatively abundant fish species during the summer were recorded mainly between the teleostean fish feeder and shrimp feeder groups. Overall, the seasonal dynamics of the waters and the consequent prey abundance influenced the resource availability. Resource partitioning and feeding plasticity allowed the species to optimize the use of available prey in the bay. These results represent a contribution toward understanding the local food web, to construct a trophic model, and to contribute to its sustainable integrated management.