Trophic ecology of two syntopic sciaenid species (Micropogonias furnieri (Desmarest, 1823) and Ctenosciaena gracilicirrhus ) (Metzelaar, 1919) in a tropical bay in south-eastern Brazil

Abstract

Analyzed were the diets of two closely related species of Sciaenidae (Micropogonias furnieri and Ctenosciena gracilicirrhus) coexisting in high abundance in the outer zone of Sepetiba Bay. Their sizes and seasonal niche dimensions were also analysed. The tested hypothesis was that these two abundant species do not overlap in the trophic niche despite occurring in the same area and having similar sizes and body shapes and where an intraspecific overlap is likely to occur. The stomach contents of 198 M. furnieri specimens (85–280 mm total length) and 198 C. gracilicirrhus (49–131 mm total length) were examined. Quarterly diurnal fish samplings were performed using bottom trawls between winter 2012 and autumn 2013. In each season, three replicate tows were taken against the current during 20 min at the bottom with a towing speed of circa 4.5 km/hr, covering a distance of approximately 1,500 m. The trawl had an 8 m headline, 11 m ground rope, 25 mm stretched mesh and 12 mm mesh cod-end liner. Significant differences were detected in the diet between the two species (Pseudo-F = 5.16; p = .001) and among size classes (Pseudo-F = 2.23; p = .001), but not among seasons (Pseudo-F = 0.36; p = .920), according to PERMANOVA. Micropogonias furnieri fed mainly on Polychaeta and Caprella, whereas C. gracilicirrhus fed preferably on Caprella. Both species tended to specialize as they grew in size, with M. furnieri preferring Polychaeta, and C. gracilicirrhus specializing in Caprella. As expected, a high intraspecific niche overlap was observed among the size classes within each species, but not at an interspecific level and with the two syntopic species using different feeding resources.