Hábitos alimentares e ecologia trófica de duas espécies sintópicas de sciaenídeos Micropogonias furnieri e Ctenosciaena gracilicirrhus em uma baía tropical no sudeste do Brasil

Abstract

The analysis of fish diet is of great importance to understand not only the coexistence of these groups of organisms, but also the processes developed in ecosystem in which they inhabit. The objective of this study was to analyze the diet of twoc Sciaenidae species, Ctenosciaena gracilicirrhus and Micropogonias furnieri and to assess the occurrence of ontogenetic and seasonal variations in diet, besides the possible mechanisms used to allow the coexistence of these abundant syntopic species in the outer zone of Sepetiba Bay. The tested hypothesis is that these species closely related in form, have partitioning of food resources to coexist in Sepetiba Bay and that occur changes in feeding habits along the growth. The stomach contents of 198 specimens of M. furnieri (85-280 mm of total length) and 198 of C. gracilicirrhus (49-131 mm in total length) obtained from quarterly daytime bottom trawls performed between the winter of 2012 and the fall of 201 in outer zone of the Bay of Septiba, RJ were examined. Different patterns in diets between species, size classes and seasons were determined by the Non-Metric Multidimensional Scalin. Significant differences were detected in the diet between the two species (Pseudo-F= 37.139, p = 0.001) and between size classes (Pseudo-F = 2.23, p = 0.001), but not between seasons (F = 0.36, p = 0.920), according to PERMANOVA. Micropogonias furnieri fed mainly on Polychaeta and Caprella, while C. gracilicirrhus preferred Caprella. Micropogonias furnieri prefered Crutacea in the smaller size classes, extending to the use of Polychaeta in larger size classes. Ctenosciaena gracilicirrhus showed preference for Caprella in larger size classes. No significant seasonal variations were observed for the two species. Both species presented a narrower trophic niche with increasing in size, thus characterizing a trend towards specialization, also confirmed through the Amundsen diagram, with M. furnieri preferring Polychaeta, and C. gracilicirrhus, Caprella. As expected, a high intraspecific overlap of intraspecific trophic niche was observed between size classes within each species, but not at an interspecific level, with both species using different dietary resources. The hypothesis that the two species closely related in form present partition of the trophic niches as a mechanism to facilitate coexistence was confirmed.