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In higher latitudes of the northern hemisphere, anadromous fishes can act as biological vectors, moving marine-derived nutrients into freshwater ecosystems during their reproductive migration. Much less information is available on the potential role of marine and estuarinerelated fishes as biological vectors in subtropical latitudes. Here, we investigated whether mullet juveniles might transport marine nutrients into the freshwater food webs of coastal streams in southern Brazil (32°17'S, 52°15'W). To test this hypothesis, we analyzed the stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) in 10 basal production sources and 10 consumer species, including juvenile mullets, at 3 sites (surf zone, lower stream reach, headwater reach) along a marine−freshwater gradient. Our results revealed a significant decreasing trend in δ 15 N and δ 13 C values from the sea to the freshwater sites, suggesting an importation and incorporation of marine-derived nutrients into the coastal stream. A mixing model showed a marked shift in assimilation from marine to freshwater production sources by mullet Mugil liza juveniles as they moved from the surf zone into the coastal stream (lower stream and headwater reaches). Our mixing model also indicated that material of marine origin is assimilated by freshwater predators, particularly those found at the lower stream reach. Further experimental and field work is needed to evaluate the implications of marine-derived carbon and nitrogen transport by juvenile mullets for the structure and dynamics of food webs in coastal streams.KEY WORDS: Brazil · Food web spatial subsidies · Freshwater piscivore · Mugil liza · Sea −land connectivity · SIAR mixing models

Resource pulsing is a widespread phenomenon, but its effects on ecosystem dynamics are often difficult to predict. Hydrological pulsing, in particular, is known to influence the structure and dynamics of fluvial and coastal ecosystems, but little information is available about its effects on trophic connectivity between wetlands and estuaries. We investigated the hypothesis that hydrologic pulsing drives 1-way trophic subsidies (e.g. suspended organic matter and freshwater fish) from wetland to estuary. Our study system is a coastal lagoon with an ephemeral mouth that, when closed, stores freshwater as a sustained flood pulse that is subsequently released when a connection with the sea is reestablished. We monitored isotopic composition of consumers and food sources over the course of an entire flood pulse to infer trophic linkages and spatial subsidies. Before the flood peak (April and May), freshwater and estuarine zones were largely dependent on local primary production sources (seston and C 3 plants vs. C 4 plants and microphytobenthos, respectively), essentially functioning as disconnected compartments. A sustained pulse of freshwater inflow (June to August) induced greater habitat connectivity and a net flow of biomass and energy from the freshwater zone into the estuarine zone. The opening of the lagoon outlet channel abruptly terminated the flood pulse and reduced freshwater subsidies to estuarine consumers, and both zones returned to dependence on autochthonous production. Our findings contribute to current concerns that artificial opening of sandbars in coastal lagoons alters natural ecological dynamics with significant effects on biodiversity and ecosystem processes.

Studies on food web structure in estuaries based on stable isotopes have usually not taken spatiotemporal variations in the isotopic variability of food web components into account. We investigated temporal and between-habitat variations in the isotopic composition ( 13 C/ 12 C and 15 N/ 14 N) of basal food sources -i.e. primary producers, particulate organic matter (POM) in the sediment or in suspension, and biofilm -and consumers and explored their implications for food web structure and dynamics. Samples of 9 basal sources (N = 224) and 6 representative invertebrates and fish (N = 303) were collected monthly over 1 yr in a marsh creek and a mudflat of the Patos Lagoon, a large southwestern Atlantic estuary. The relative contributions of food sources to consumers were estimated by mixing models. Overall, δ 13 C values of food sources and consumers were higher (p < 0.05) in the mudflat, whereas δ 15 N values were enriched (p < 0.05) in the marsh creek for most primary producers and consumers. C and N isotope values varied on both monthly and seasonal scales, with several food sources and consumers exhibiting higher values (p < 0.05) during the spring and summer. The primary food sources were POM in the sediment, C 4 plants (e.g. widgeon grass), and, to a lesser extent, suspended POM. Biofilm and macroalgae were also food sources for consumers in the marsh creek and mudflat, respectively, especially during warmer seasons. Our findings corroborate the hypothesis that the Patos lagoon food web is spatially structured and supported by local basal sources and detritus of different origins, which can be seasonally important for consumers in each particular habitat.KEY WORDS: Estuarine food web · Salt marsh detritus · Mixing model · SIAR · Widgeon grass · Biofilm · Fish · Decapod crustaceans · Temporal variability Resale or republication not permitted without written consent of the publisher

Pseudis minuta is abundant in a variety of aquatic environments of the Pampa domain. Therefore, it can be considered a good model for testing hypotheses on environmental heterogeneity and the influence of climate on the activity of anurans. In this study, we examined the spatial distribution pattern of P. minuta in terms of microhabitats and the influence of abiotic factors on seasonal fluctuations in the abundance of this species. Samples were collected monthly from April 2008 to May 2009 in wetlands and coastal dunes in the Lagoa do Peixe National Park. A total of 112 specimens of P. minuta were collected, of which 45 were found in the wetland area and 67 in the dune area. The species showed seasonal fluctuation in abundance, and it was most abundant in months with higher temperatures (spring-summer). Pseudis minuta was mainly associated with aquatic vegetation, an expected pattern in terms of their morphological adaptations to this environment. Among the abiotic parameters analyzed, only the monthly mean temperature showed a significant correlation (p < 0.05; r = 0.67) with the abundance of P. minuta. We concluded that P. minuta is a generalist species with respect to microhabitat use and also that fluctuation in its population abundance is mainly associated with seasonal variation in temperature.Keywords: abundance, anuran, coastal plain, Lagoa do Peixe, spatiotemporal distribution.Padrão de atividade e uso de micro-habitat de Pseudis minuta Günther, 1858 (Anura, Hylidae) no Parque Nacional da Lagoa do Peixe, uma reserva da biosfera na região subtropical do Brasil ResumoPseudis minuta é uma espécie abundante em diferentes tipos de ambientes aquáticos do domínio Pampa. Por essa razão, essa espécie pode ser considerada um bom modelo para testar hipóteses relacionadas à heterogeneidade ambiental e à influência do clima sobre padrões de atividade em anuros. Neste trabalho, foi avaliado o padrão de distribuição espacial de P. minuta em termos de micro-habitats, além de se avaliar a influência de fatores abióticos nas flutuações sazonais da abundância dessa espécie. Coletas foram realizadas mensalmente, entre abril de 2008 e maio de 2009, em áreas úmidas e de cordões de dunas costeiras no Parque Nacional de Lagoa do Peixe. Um total de 112 indivíduos de P. minuta foi coletado, sendo 45 em áreas de banhado e 67 em área de dunas. A espécie apresentou flutuação sazonal na abundância, sendo mais abundantes em meses com temperaturas mais elevadas (primavera-verão). Pseudis minuta esteve associada principalmente à vegetação aquática, um padrão esperado em função de suas adaptações morfológicas a esse meio. Entre os parâmetros abióticos analisados, somente a temperatura média mensal apresentou correlação significativa (p < 0.05; r = 0,67) com a abundância de P. minuta. Foi possível concluir que P. minuta é uma espécie generalista com relação ao uso do habitat e que as flutuações na sua abundância populacional estão principalmente associadas à variação sazonal da temperatura.Palavras-chave: abundância, anuro, planí...

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We investigated the diet, feeding strategy, size-related dietary shifts and prey preferences of South American Hoplias aff. malabaricus in an internationally recognized but poorly investigated Biosphere Reserve in southern Brazil. Fish were caught between April 2008 and March 2009 using a variety of fishing gear. The analysis of 113 individuals revealed a diet essentially composed of fish (16 species), particularly characid species (9). The diet became more diverse and contained larger fish prey with increasing predator size. Feeding strategy analysis revealed a clear specialization towards the consumption of fish. However, individuals did not prey upon particular prey species, instead opportunistically consuming many different fish species, which could be a strategy to avoid intraspecific competition. Characid species were the most important prey, followed by poecillids. A multi-gear sampling of the ichthyofauna revealed that these prey species were the most abundant (Characidae: 61.3%, Poeciliidae 18.8%) of the 14 fish families occurring at the study site, suggesting that the predator exploits the most abundant fish resources available rather than the rarer fish prey. These findings suggest that potential topdown controls exerted by H. aff. malabaricus in this system follow specific food web pathways that seem to be mediated by the abundance of prey resources.