Abstract Eutrophic estuaries receive organic matter (OM) inputs from multiple sources. This study evaluated the distribution and origin of sedimentary OM in an eutrophic estuary (Pina Sound, NE Brazil). Thirteen samples were collected in the sublittoral in addition to major local sources. Biochemical (chlorophyll - Chl), elemental [(C/N)a and C/S ratios] and isotopic (δ 15N and δ 13C) analyses were carried out for characterizing OM and redox conditions. The SIAR mixing model was used to quantify contribution from main sources. At Pina Sound, distribution of OM is associated with mud, reflecting the hydrodynamics control on deposition of suspended particles. Microphytobenthic production is limited ([Chl a] < 1000 µg/g organic carbon) in the sublittoral where the Chl degradation products prevail (mean [Pheopigments] = 2643 ± 958 µg/g organic carbon). Anoxic conditions (C/S ratio ≈ 2) are typically observed in sediments of deeper portions of Pina Sound. Such sediments receive high organic loads and are subject to poor water renewal. According to SIAR mixing model, sedimentary OM of Pina Sound is composed of, on average: 50% phytoplankton, 24% sewage and 26% C3 plants. This reflects fertilization of Pina Sound with high loads of untreated sewage. Pina Sound has a great potential to retain sewage-derived OM.

Characidium rachovii (Regan, 1913) é uma espécie frequente em riachos da planície costeira do estado do Rio Grande do Sul, sul do Brasil. Entretanto, seu nicho trófico é ainda desconhecido. O presente trabalho teve como objetivos: (i) descrever a dieta de C. rachovii de três riachos costeiros do RS; (ii) avaliar a influência de um ecótono (mar-riacho) na dieta, comparando dois locais, um próximo do mar e outro distante, e (iii) avaliar o efeito do número de indivíduos analisados na riqueza da dieta. A análise do conteúdo estomacal de 139 indivíduos revelou que a espécie é especializada no consumo de Diptera (estágio aquático) e Amphipoda. Ao mesmo tempo, pode-se considerar que C. rachovii apresentou hábito alimentar oportunista, já que, apesar de tal preferência, consumiu grande riqueza de recursos (24 itens), vários deles em baixa frequência e alta abundância. Não houve diferenças na composição da dieta entre os riachos e locais. A riqueza esperada (rarefação) mostrou que o número de indivíduos analisados altera a estimativa de riqueza da dieta em espécies que consomem itens raros.

Characidium rachovii (Regan, 1913) is a frequent species in coastal plain streams on state of Rio Grande do Sul, southern Brazil. However, its trophic niche is still unknown. This paper aimed to: (i) describe the diet of C. rachovii in three coastal plain streams of RS; (ii) evaluate the influence of an ecotone (sea-stream) in the diet by comparing two sites, one near and other distant of the sea, and (iii) evaluate the effect of individuals number analyzed on the richness of the diet. The stomach contents analysis of 139 individuals revealed that the species was a specialist in Diptera (aquatic stage) and Amphipoda. Characidium rachovii was also opportunist, since besides such preference, consumed great richness of resources (24 items) and various with low frequency and high abundance. There were no differences in diet composition among streams and sites. The expected richness (rarefaction) showed that the number of individuals analyzed changes the estimate of diet richness in species that consume several items at low frequency.

Apesar da sua ampla distribuição e importância para o comércio aquariofilista, muitos aspectos da biologia do cará Geophagus brasiliensis no seu habitat natural, como a relação entre sua ecologia alimentar e comportamento reprodutivo, ainda não são bem conhecidos. Nesse trabalho foi investigada sua dieta, enfocando como as diferenças na dieta e no consumo alimentar estão relacionadas ao sexo (macho/fêmea) e a maturidade (imaturo/maturo). O trato digestório de cada indivíduo foi dissecado e teve seu conteúdo analisado, enquanto cada gônada foi analisada microscopicamente para determinar o sexo e a maturidade. Um total de 28 fêmeas e 31 machos foram analisados. Indivíduos maturos foram mais comuns do que espécimes imaturos, tanto para machos (64,50%) quanto para fêmeas (64,30%). A análise de 52 indivíduos com alimento no trato revelou uma dieta composta por 27 itens. De acordo com o Índice de Importância Alimentar (%IAi), os itens alimentares mais importante na dieta foram Gastropoda (37,30%), fragmentos de plantas vasculares (15,16%), detrito (10,14%), Amphipoda (9,24%) e escamas de peixe (6,29%). Machos maturos tiveram mais estômagos vazios (65,00%) quando comparados com machos imaturos (27,27%) e fêmeas imaturas (55,56%) e maturas (40,00%). Além disso, fêmeas maturas apresentaram maior consumo de alimentos (valor médio do volume total de alimentos) do que machos maturos. Algumas hipóteses são propostas na tentativa de explicar se essa diferença no consumo de alimento entre machos e fêmeas maturos está relacionada ao desenvolvimento de caracteres sexuais primários e secundários, ou com a assimetria na quantidade de tempo empregado em atividades relacionadas ao cuidado parental.

Despite the importance of the pearl cichlid Geophagus brasiliensis for the aquarium fish trade worldwide and its wide distribution, many aspects of its biology, such as the relationships between its feeding ecology and reproductive behavior, are not fully understood in natural conditions on its native habitat. In this paper, we investigated its diet focusing on how differences in diet and food consumption are related to differences in gender and sexual maturity. The digestive tract of each individual was dissected and had its content analyzed, whereas each gonad was microscopically analyzed to determine gender (male/female) and sexual maturity (immature/mature). A total of 28 females and 31 males were analyzed. Mature individuals were more common than immature specimens both for males (64.50%) and females (64.30%). The analysis of 52 individuals with non-empty digestive tracts revealed a diet comprised of 27 items. According to the Index of Alimentary importance (%IAi), the most important food items in the diet were Gastropoda (37.30%), fragments of vascular plants (15.16%), detritus (10.14%), Amphipoda (9.24%), and fish scales (6.29%). Mature males had more empty stomachs (65.00%) when compared to immature males (27.27%) and immature (55.56%) and mature females (40.00%). Also, mature females seemed to have more food consumption (greater mean values of total volume) in their digestive tracts than mature males. Some hypotheses are proposed in order to distinguish if this gender-based difference in food consumption in mature individuals of the pearl cichlid could be associated with the development of primary and secondary sexual characteristics or with asymmetrical time invested in parental care activities.