Abstract Aquatic macrophytes are the main autochthonous component of primary production in the Amazon Basin. Floating meadows of these plants support habitats with highly diverse animal communities. Fishes inhabiting these habitats have been assumed to use a broad range of food items and compose a particular food web. We employed carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to draw the trophic structure of these habitats and to trace the energy flow by its trophic levels. Fishes and other animals from 18 independent macrophyte meadows of a floodplain lake of the Solimões River (Amazonia, Brazil) were analyzed. The food web of macrophyte meadows consists of four trophic levels above autotrophic sources. In general, primary consumers exhibited a broader range of food sources than the upper trophic levels. Some fish species depended on a large number of food sources and at the same time are consumed by several predators. The energy transfer from one trophic level to the next was then mainly accomplished by these species concentrating a high-energy flux and acting as hubs in the food web. The broad range of δ13C values observed indicates that the organisms living in the macrophyte meadows utilize a great diversity of autotrophic sources. Basin communities δC δ C (δ13C δ15N δN N (δ15N 1 Amazonia, Amazonia (Amazonia Brazil analyzed general predators highenergy high

An assessment of mercury (Hg) concentrations and nitrogen stable isotope (δ15N) was conducted in the food chain of the Atlantic spotted dolphin (Stenella frontalis), including phytoplankton, zooplankton, planktivorous fish and its major prey (predatory fish and a single species of cephalopod), that compose a tropical trophic chain of the Brazilian southeastern coast. Tissue concentrations of Hg in a voracious predator fish, the largehead hairtail (Trichiurus lepturus), one of the dolphin's prey, were 9.8 times lower than median concentrations found in dolphin tissues. δ15N values in predatory fish were found to be lower to those of its predator the spotted dolphin. Isotopic data suggested significant differences for δ15N along the trophic chain, with the top predator (dolphin) exhibiting heavier value, followed by the voracious predator fish and the benthonic carnivorous fish, the whitemouth croaker (Micropogonias furnieri). Phytoplankton displayed the lightest δ15N, followed by zooplankton and the planktophagous fish, the lebranche mullet (Mugil liza). This fish species and the cephalopod showed the lowest median Hg concentration. All links of the entire trophic chain presented trophic transfer of Hg with a biomagnification factor higher than 1. A significant relationship was found between the log Hg concentration and trophic level (TL) of all evaluated species, with a positive slope (β= 0.87). The calculated trophic magnification factor (TMF= 7.44) indicates that Hg concentration increased per TL, and also that the entire coastal food chain from the South Atlantic Ocean presented a biomagnification power of Hg within a range previously reported for tropical coastal ecosystems.

Se realizó una evaluación de las concentraciones del mercurio (Hg) y del isótopo estable de nitrógeno (δ15N) en la cadena trófica del Delfín Moteado del Atlántico (Stenella frontalis), incluyendo fitoplancton, zooplancton, peces planctívoros y sus principales presas (peces depredadores y una sola especie de cefalópodo), componentes de una cadena trófica tropical de la costa sureste de Brasil. Una de las presas del delfín, un pez depredador voraz, el pez sable (Trichiurus lepturus), presentó una concentración mediana del Hg 9,8 veces inferior que la del delfín. El valor de δ15N es más bajo que al de su depredador. Los datos del isótopo han sugerido que ha habido diferencias significativas para el δ15N a lo largo de la cadena trófica, en la que en el mayor depredador (delfín) se ha mostrado más pesado, seguido por el pez depredador y el pez bentófago, la corvina (Micropogonias furnieri). Se ha observado que el fitoplancton presentó el δ15N más liviano, seguido por el zooplancton y el pez planctófago, el lebranche (Mugil liza). Este pez y el cefalópodo han mostrado la mediana más baja de Hg. Se han encontrado transferencias mayores que 1 en todos los vínculos de la cadena evaluada. Se ha obtenido una relación significativamente positiva entre la concentración del Hg (en logaritmo) y el nivel trófico (TL), incluyendo todas las especies investigadas, presentando una pendiente positiva (β= 0,87). El factor de magnificación trófica (FMT= 7,44) indica que la concentración del Hg ha aumentado per TL, y también que toda la cadena trófica costera presentó un poder de biomagnificación de Hg dentro de un rango previamente reportado para ecosistemas costeros tropicales.

ABSTRACT Barium (Ba) is a trace element which occurs predominantly as barite mineral (BaSO4) in the marine environment. Previous work suggests that barite concentrations are related to the organic carbon flux and marine biological debris in the water column suggesting a direct or indirect involvement in the marine biological cycling. In addition, barite has a high preservation rate (~30%) in sediments and it is less affected by early diagenesis than other proxies for productivity such as carbonates (~10%) and organic carbon (~1%), for example. Therefore, Ba is considered an excellent proxy for ocean (paleo)productivity. However, correlating barite to productivity involves some caveats. Specifically, the post-depositional formation of barite in oxic sediments can lead to Ba release into porewaters under anoxic conditions, which can form barite again under oxic conditions. This diagenetic formation is not correlated to export production as the seawater authigenic barite formed with decaying organic matter in the water column. Therefore, the main goal of this work is to briefly review the marine Ba cycle and highlight its importance for (paleo)productivity research.

As adaptações ecofisiológicas de aguapé (hiperacumuladora de metais) sob condições ambientais adversas ainda não estão totalmente elucidadas. Este trabalho avaliou pigmentos fotossintéticos e fluorescência da clorofila a em aguapé coletados em diferentes regiões (alto, médio e baixo) do rio Paraíba do Sul (RPS) e no rio Imbé, Brasil. Adicionalmente Mn, Fe, Zn, Cu, Pb e Ni foram quantificados na parte área e raízes. Ferro e Mn foram os elementos detectados em maiores concentrações em todas as amostras. Zinco e Cu foram detectados em maiores concentrações nas raízes de plantas do médio e alto RPS, locais de grande atividade antropogênica. As mais elevadas concentrações de quase todos os metais foram verificadas nas plantas do médio RPS. Com relação às adaptações fotossintéticas, plantas do médio e alto RPS mostraram as maiores concentrações de pigmentos fotossintéticos, assim como os mais elevados valores de Fv/Fm e Fv/F0. As avaliações fotossintéticas destas plantas sugerem que elas não estejam sob condições de estresse, mesmo nas regiões de grande atividade antropogênica. Correlação positiva foi observada entre quenching não-fotoquímico e carotenóides, sugerindo que a dissipação de energia na forma de calor seja uma estratégia para manter o funcionamento fotossintético fotoquímico estável, confirmado pelos valores de Fv/Fm. É possível que esta estratégia adaptativa seja eficiente como resposta de longo prazo, uma vez que na literatura esta não parece ser a via preferencial de adaptação a estresses de curto prazo, avaliados sob condições controladas.

The ecophysiological adaptations of water hyacinth (metal hyperaccumulator) under adverse environmental conditions are not yet clearly elucidated. This work evaluated photosynthetic pigments and chlorophyll a fluorescence in water hyacinth plants sampled in different regions (upper, middle and lower) of Paraíba do Sul river (PSR) and Imbé river, Brazil. Additionally Mn, Fe, Zn, Cu, Cr, Pb and Ni were quantified on the shoots and roots. Roots were the preferential site of metal accumulation. Cromium was not detected in the shoots. Iron and Mn were the elements detected in higher concentrations in all samples. Zinc and Cu were detected in higher concentrations in roots of plants from middle and upper PSR, sites of higher anthropogenic activity. The highest concentrations of almost all metals were verified in plants from middle PSR. Regarding photosynthetic adaptations, plants from middle and upper PSR showed the highest concentrations of photosynthetic pigments, as well as the highest values of Fv/Fm and Fv/F0. The photosynthetic performance of plants suggests that they are not under stress conditions, even in regions of higher anthropogenic activity. Positive correlation was observed among nonphotochemical quenching and carotenoids, suggesting dissipation of energy in the form of heat as an strategy to keep the stable photochemical photosynthesis functioning, confirmed by values of the Fv/Fm. It is possible that such adaptative strategy is efficient as a long term response to stress factors, once literature data suggest that this is not a preferential path for photosynthesis in stress circumstances under short time controlled conditions.