Relações tróficas de três espécies de peixes abundantes (Eucinostomus argenteus, Diapterus rhombeus e Micropogonias furnieri) na Baía de Sepetiba

Abstract

The aim of this study was to determine spatial, seasonal and ontogenetic changes in diet of three abundant fishes species (Eucinostomus argenteus, Diapterus rhombeus and Micropogonias furnieri) which use the Sepetiba Bay as recruitment and rearing grounds, to test the hypothesis that they would be using the variation along the trophic axis as strategy to coexist. Two fishing sampling programmes were carried out during the day and night period: one by using beach seine to catch juveniles in two different locales of the bay, Itacuruçá beach located in the outer zone, and Sepetiba beach, located in the inner zone; and the other by using bottom trawls to catch subadults/adults in three bay zones (inner, middle and outer), defined according to environmental gradient (temperature, salinity, depth and transparency) of sea proximity. A total of 2075 stomachs were analyzed, being 769 E. argenteus (489 juveniles and 280 adults), 537 D. rhombeus (250 juveniles and 287 adults) and 769 M. furnieri (483 juveniles and 286 adults). Variations in the diet along the spatial axis were detected, reflecting the use of the available items in each areas. It the sandy beaches, where recruitment take places, juveniles uses mainly items from zooplankton, while in deeper bay areas, subadults/adults use items associated to substrate. E. argenteus juveniles showed as main preys Apendicularia, Calanoida, Tanaidacea and Polychaeta, while subadults/adults, Polychaeta, Harpacticoida and Caprella. D. rhombeus juveniles use mainly Tanaidacea, Apendicularia, Cyclopoida and Calanoida, while for subadults/adults Harpacticoida was the most important item. M. furnieri juveniles, catched in Sepetiba becah only, showed a diet basically comprised by two principal items, Cyclopoida and Polychaeta, while subadults/adults showed Polychaeta sp. 1, Polychaeta, Harpacticoida and Caprella. Ontogenetics changes in diet were evidenced for M. furnieri only, with individuals of size <30 mm showed Cyclopoida as the principal item, while larger fishes use Polychaeta as predominant item in diet. Seasonal changes were not evident, although peaks in species abundances in different seasons indicates resources partition, as observed for M. furnieri and D. rhombeus in the beaches. Migration to deeper areas during the development of species and differentiated proportion of items in diet seems to be the strategy developed by these three species to avoid competition, since overlapping in trophic niche was low among the species. Only M. furnieri and D. rhombeus showed indication of significantly biological interspecific overlapping, due to similarity in principal preys. Intraspecific trophic overlapping was significant among the smallest size classes, due to morphological constraints to use a larger number of preys. This model was also indicated by low niche width for the smallest size classes. The generalist feeding strategy was used by the three species, with D. rhombeus showing the most generalist behavior compared to the other two species due to larger niche width. Both E. argenteus and D. rhombeus showed feeding activity during the day, while M. furnieri fed all they long, without difference between the day and the night. Interespecific and intraspecific differences in diet and in the feeding activity enable resource partitioning, reducing potential for competition, and allowing coexistence of these species in the Sepetiba bay.