We investigated the trophic niches and the resource partitioning of two snook species, the common (Centropomus undecimalis) and the fat snook (C. parallelus), in four tropical estuaries of the northeastern Brazil, using stable isotope analyses of carbon (δ13C) and nitrogen (δ15N). Fish specimens, mainly juveniles, basal resources and a primary consumer were collected in 2015 during dry and rainy seasons in all estuaries, which exhibited differences in system size, geomorphologic shapes, levels of sea access and anthropic pressures. Potential effect of factors like fish body length, estuary and seasonality on isotope ratios were investigated. Positive relationships between the size of fish and δ15N values were found, regardless the species. Our results indicated that snooks can be characterized as secondary consumers and have close trophic niches in most estuaries. Trophic overlaps were more pronounced within the largest estuaries (Catuama and Santa Cruz), whereas smaller systems that have restricted connections to the sea presented low isotopic niche overlap between both species (Suape and Sirinhaém). Moreover, a higher variability of δ13C and δ15N values in snooks was found in larger estuaries undergoing stronger influences from coastal adjacent waters. Although we were not able to detect clear seasonal effects, greater isotopic overlaps were found during the rainy season. Despite the lack of intrinsic differences in life history traits, both species, dominated by juveniles, shared similar trophic niches in these environments. Highlights ► δ 13 C and δ 15 N of two Centropomidae were investigated in four estuaries in Brazil. ► Juveniles of Centropomus undecimalis and C. parallelus have close isotopic niches. ► Trophic overlaps were more pronounced in large estuaries. ► Resource partitioning process might reflects the resource availability in estuaries.

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We used complementary stable isotope (SIA) and stomach content (SCA) analyses to investigate feeding relationships among species of the nektobenthic communities and the potential ecological effects of the bottom trawling of a coastal ecosystem in northeastern Brazil. Carbon (δ13C) and nitrogen (δ15N) compositions were determined for five basal sources and 28 consumers, from zooplankton to shrimp and fish species. Fishes and basal sources showed a broad range of δ15N (fishes: 6.49–14.94‰; sources: 2.58–6.79‰) and δ13C values (fishes: -23.86 to -13.71‰; sources: -24.32 to -13.53‰), while shrimps and crabs exhibited similar nitrogen and carbon ratios. Six trophic consumer groups were determined among zooplankton, crustaceans and fishes by SIA, with trophic pathways associated mostly with benthic sources. SCA results indicated a preference for benthic invertebrates, mainly worms, crabs and shrimps, as prey for the fish fauna, highlighting their importance in the food web. In overall, differences between SCA and the SIA approaches were observed, except for groups composed mainly for shrimps and some species of high δ15N values, mostly piscivorous and zoobenthivores. Given the absence of regulation for bottom trawling activities in the area, the cumulative effects of trawling on population parameters, species composition, potentially decreasing the abundance of benthic preys (e.g., shrimps, worms and crabs) may lead to changes in the trophic structure potentially affect the food web and the sustainability of the fishery.

Gonzalez and Vaske Junior: Feeding of Atherinella blackburni in Brazil 346Feeding ecology of the beach silverside Atherinella blackburni (Atherinopsidae) in a tropical sandy beach, Southeastern Brazil A ecologia alimentar do peixe-rei (Atherinella blackburni) na zona de arrebentação de uma praia arenosa tropical, localizada no sudeste do Brasil, foi acessada a partir da análise do conteúdo alimentar de 198 peixes. Fatores como o tamanho, a estação do ano e o período do dia foram analisados para compreender como estes influenciam a dieta da espécie. Os resultados mostram que A. blackburni é um peixe nerítico costeiro com amplo nicho alimentar. As presas mais recorrentes foram os crustáceos zooplanctônicos, insetos e moluscos bentônicos, sendo os crustáceos da subclasse Copepoda o item dominante na dieta em ocorrência e abundância. A. blackburni aparenta possuir uma leve mudança ontogênica em sua dieta, variando de moluscos bentônicos para crustáceos e em seguida para insetos ao longo do seu ciclo de vida. A atividade diária também demonstrou ser um fator importante para a ecologia alimentar de A. blackburni. O predomínio de peixes pequenos durante o período da manhã, juntamente com as principais presas para esta classe de tamanho, sugere que indivíduos pequenos utilizem as áreas mais rasas para alimentação durante o período da manhã e, durante a noite, movem-se para águas mais profundas em busca de proteção contra predadores. A. blackburni appears to have a slight ontogenetic shift in its diet, changing from benthic molluscs to crustaceans and insects along its life cycle. The diel activity also reveals to be an important factor to the A. blackburni feeding ecology. The predominant occurrence of small fish during the morning, along with the main preys for this size class, suggests that small individuals use shallower waters as feeding grounds during the morning and, during the night, they move to deeper waters for protection against predators. Resumo AbstRActDescriptors: Diel activity, Diet, Ontogenetic shift, Resources partitioning, Surf zone, Zooplanktivorous.

This study provides information about the feeding habits, population aspects and spatial distribution of the spot­ted goatfish, Pseudupeneus maculatus, along the coast of the tropical Brazilian continental shelf. Distribution patterns are described using length frequencies and catch rates. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N), along with stomach contents, were analysed to determine the diet of the spotted goatfish. Multivariate analysis and numerical indicators of the diet, such as numerical frequency, frequency of occurrence and weight percentage, were computed to evaluate the diet composition. The mean trophic position was defined using both stable isotope ratios and stomach content analysis. The length at first maturity for the species was determined as 13.7 cm. A slight pattern in size distribution was observed, with mean size increasing with depth along the shelf. The diet was mainly composed of crustaceans, teleosts and Polychaeta. No clear dietary difference was found between habitat types, water depth or latitude. Both trophic positions estimated by stable isotopes and stomach contents analysis ranged between levels 3 and 4. P. Maculatus was found to be feeding on many rare and infrequent prey items, classifying it as a generalist zoobenthivorous predator, probably due to its efficient search strategy.

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