Trophic assessment and isotopic niches of the sympatric penaeids species Penaeus brasiliensis and P. paulensis in SW Atlantic estuarine systems

Abstract

ABSTRACT Penaeus brasiliensis and P. paulensis are shrimp species which overlap their distribution only in the Southwest Atlantic. In addition, they are fishery resources intensively exploited. The interactions between these two sympatric species, especially sharing of food resources, are still unknown. We have investigated the niche breadth of juvenile pink shrimps in two proximal coastal nurseries (Sepetiba and Guanabara bays) located in Southeast Brazil (∼23°W) by means of stable isotopes and stomach content analyses. These two bays are important nurseries for these species and are located in one of the most populous regions of Brazil. Diets were basically composed of benthic invertebrates (mollusks, crustaceans and polychaetes), particulate organic matter and benthic diatoms. We detected significant spatial differences in isotopic compositions (δ13C and δ15N), with pink shrimps from Guanabara Bay displaying the lowest values of both isotopes. The δ13C range and diet support that benthic microalgae are the primary producers in P. brasiliensis and P. paulensis food chains. Trophic diversity was higher in Guanabara Bay based on δ15N range, Standard Ellipse Area, and Centroid Distance metrics, displaying greater individual variability in isotopic signatures compared to Sepetiba Bay, probably due to enhanced food diversity and spatial heterogeneity in the former. The overlap in the ellipses areas between the two shrimp species was greater in Sepetiba Bay and indicates a greater sharing of resources that should be more abundant and available. Niche metrics analysis revealed greater spatial rather than interspecific differences. We advocate paying particular attention to monitoring the pink shrimps of Sepetiba Bay due to their smaller trophic niche width and lower δ15N range, which increases their sensitivity to changing habitat, mainly due to human actions.