| Summary: | The genus Haemulon contains some of the most abundant and ecologically important reef fishes in the South Atlantic Ocean. However, their life history attributes have not been widely studied. Knowledge of ontogenetic changes in their resource use is critical to understanding the processes structuring natural communities. The present study analysed ontogenetic diet changes and food partitioning in Haemulon spp. We collected stomach contents from 276 individuals of four different size classes from four sympatric species (H. aurolineatum, H. parra, H. plumieri and H. squamipinna). There was a significant difference in the proportions of prey types between both species and size classes, providing evidence of food partitioning. Moreover, the Bray–Curtis similarity index revealed two distinct groups. The first consisted of larger-sized fish that consumed larger food items and the second group consisted of smaller individuals that fed on small invertebrates. There was an abrupt shift in the diet of Haemulon spp. at around 10.0 cm total length, a size that corresponds with the greatest morphological changes in the genus. Additionally, the diet overlap calculated by Pianka's index was more evident in smaller and larger size classes than in intermediate individuals. Together, these observations suggest Haemulon species undergo ontogenetic diet changes and food partitioning within species and size classes that are associated with changes in their habitat use, alongside morphological changes. Further research is needed to determine their ecomorphology and the competitive mechanisms that allow the coexistence of several sympatric and ecologically similar species of the genus Haemulon.
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