A B S T R A C TThe rising of cold water from deeper levels characterizes coastal upwelling systems. This flow makes nutrients available in the euphotic layer, which enhances phytoplankton production and growth. On the Brazilian coast, upwelling is most intense in the Cabo Frio region (RJ). The basic knowledge of this system was reviewed in accordance with concepts of biophysical interactions. The high frequency and amplitude of the prevailing winds are the main factor promoting the rise of South Atlantic Central Water, but meanders and eddies in the Brazil Current as well as local topography and coast line are also important. Upwelling events are common during spring/summer seasons. Primary biomass is exported by virtue of the water circulation and is also controlled by rapid zooplankton predation. Small pelagic fish regulate plankton growth and in their turn are preyed on by predatory fish. Sardine furnishes an important regional fish stock. Shoreline irregularities define the embayment formation of the Marine Extractive Reserve of Arraial do Cabo making it an area with evident different intensities of upwelled water that harbors high species diversity. Consequently, on a small spatial scale there are environments with tropical and subtropical features, a point to be explored as a particularity of this ecosystem. R E S U M OOs sistemas costeiros de ressurgência são caracterizados pela ascensão de águas frias que tornam os nutrientes disponíveis na camada eufótica para o crescimento e aumento da produção fitoplanctônica. No Brasil, a região do Cabo Frio (RJ) é o principal sistema de ressurgência costeira. O objetivo desse artigo foi revisar o atual conhecimento desse sistema através dos conceitos sobre interações biofísicas. A ascensão da Água Central do Atlântico Sul ocorre devido à alta frequência e amplitude dos ventos, à presença de meandros e vórtices na Corrente do Brasil, além da topografia local e da linha de costa. Os eventos de ressurgência são comuns durante os períodos de primavera/verão e a biomassa primária é exportada devido à circulação da água, sendo também controlada pela rápida predação zooplanctônica. Os pequenos peixes pelágicos regulam o crescimento do plâncton e são consumidos pelos peixes predadores, resultando em um importante estoque pesqueiro regional. A irregularidade da costa define as enseadas do Cabo Frio, na Reserva Extrativista Marinha do Arraial do Cabo, apresentando distintas influências das águas ressurgidas e resultando em grande diversidade de espécies. Consequentemente, ambientes com características tropicais e subtropicais são observados dentro de uma pequena escala espacial, o que constitui uma particularidade desse ecossistema.

BackgroundUpwelling systems are characterised by an intense primary biomass production in the surface (warmest) water after the outcrop of the bottom (coldest) water, which is rich in nutrients. Although it is known that the microbial assemblage plays an important role in the food chain of marine systems and that the upwelling systems that occur in southwest Brazil drive the complex dynamics of the food chain, little is known about the microbial composition present in this region.Methodology/Principal FindingsWe carried out a molecular survey based on SSU rRNA gene from the three domains of the phylogenetic tree of life present in a tropical upwelling region (Arraial do Cabo, Rio de Janeiro, Brazil). The aim was to analyse the horizontal and vertical variations of the microbial composition in two geographically close areas influenced by anthropogenic activity (sewage disposal/port activity) and upwelling phenomena, respectively. A lower estimated diversity of microorganisms of the three domains of the phylogenetic tree of life was found in the water of the area influenced by anthropogenic activity compared to the area influenced by upwelling phenomena. We observed a heterogenic distribution of the relative abundance of taxonomic groups, especially in the Archaea and Eukarya domains. The bacterial community was dominated by Proteobacteria, Cyanobacteria and Bacteroidetes phyla, whereas the microeukaryotic community was dominated by Metazoa, Fungi, Alveolata and Stramenopile. The estimated archaeal diversity was the lowest of the three domains and was dominated by uncharacterised marine Crenarchaeota that were most closely related to Marine Group I.Conclusions/SignificanceThe variety of conditions and the presence of different microbial assemblages indicated that the area of Arraial do Cabo can be used as a model for detailed studies that contemplate the correlation between pollution-indicating parameters and the depletion of microbial diversity in areas close to anthropogenic activity; functional roles and geochemical processes; phylogeny of the uncharacterised diversity; and seasonal variations of the microbial assemblages.

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resuMoO metilmercúrio é um poluente altamente neurotóxico que se acumula nos organismos e biomagnifica ao longo da cadeia trófica. O metilmercúrio é formado através de uma reação de transferência de um grupamento metil para o mercúrio inorgânico. Essa transformação, denominada metilação, é mediada principalmente por microrganismos que habitam ambientes anóxicos. A metilação pode ser abiótica como resultado de uma reação não-enzimática na transferência do grupamento metil por via fotoquímica ou interação com substâncias húmicas presentes nos corpos d'água, porém com uma taxa de metilação menor do que pela mediada por microrganismos. As taxas de metilação de mercúrio em sistemas aquáticos são influenciadas tanto pela especiação do mercúrio quanto por sua biodisponibilidade. Diversas variáveis ambientais, que se interrelacionam, tais como a atividade biológica dos microrganismos metiladores, disponibilidade de nutrientes, pH, temperatura, potencial redox, e a presença de complexos orgânicos e inorgânicos podem afetar as taxas de metilação. A importância de cada um desses fatores na produção de metilmercúrio pode variar em diferentes ecossistemas. Palavras-chave: metilmercúrio, microorganismos, ciclo global, metilcobalamina, mercúrio inorgânico, especiação. abstractMercury in aquatic systeMs: environMental Factors aFFecting Mercury Methylation. Methylmercury is a highly neurotoxic contaminant that accumulates in organisms and biomagnifies along the food chain. Methylmercury is formed through the transfer of a methyl group to the inorganic mercury (Hg 2+ ). This reaction is mainly mediated by microorganisms living in anoxic environments like bottom sediments and macrophytes rhizosphere. Abiotic methylation can also occur, however in most cases with lower rates than biological methylation. Mercury methylation rates in aquatic systems are influenced by both the speciation and bioavailability of mercury. Many interrelated environmental variables such as biological activity, nutrient availability, pH, temperature, redox potential, and the presence of inorganic and organic complexing agents can also affects the net rate of methylmercury production. Which factors dominate methylmercury production is likely to differ from one ecosystem to other. Key-words: methylmercury, microorganisms, global cycle, methylcobalamin, inorganic mercury, speciation. breve histórico do MercúrioO mercúrio é conhecido e utilizado pelo homem por mais de 3.500 anos. Provavelmente a aplicação mais antiga seja como pigmento vermelho em pinturas rupestres na forma de sulfeto de mercúrio (HgS). Pouco se sabe sobre quando o mercúrio foi isolado pela primeira vez ou a tecnologia utilizada neste processo na antiguidade. A primeira referência escrita deste metal foi feita por Aristóteles no quarto século AC que o chamou de prata líquida (hydrargyrum) dando origem ao símbolo Hg. Aristóteles e outros autores gregos como Plínio e Dioscorides descreveram aplicações medicinais como o tratamento de doenças de pele e fizeram também referências ao uso de mer...

The ecological interaction between microorganisms and seaweeds depends on the production of secondary compounds that can influence microbial diversity in the water column and the composition of reef environments. We adapted the (3)H-leucine incorporation technique to measure bacterial activity in biofilms associated with the blades of the macroalgae Sargassum spp. We evaluated (1) if the epiphytic bacteria on the blades were more active in detritus or in the biofilm, (2) substrate saturation and linearity of (3)H-leucine incorporation, (3) the influence of specific metabolic inhibitors during (3)H-leucine incorporation under the presence or absence of natural and artificial light, and (4) the efficiency of radiolabeled protein extraction. Scanning electron microscopy showed heterogeneous distribution of bacteria, diatoms, and polymeric extracellular secretions. Active bacteria were present in both biofilm and detritus on the blades. The highest (3)H-leucine incorporation was obtained when incubating blades not colonized by macroepibionts. Incubations done under field conditions reported higher (3)H-leucine incorporation than in the laboratory. Light quality and sampling manipulation seemed to be the main factors behind this difference. The use of specific metabolic inhibitors confirmed that bacteria are the main group incorporating (3)H-leucine but their association with primary production suggested a symbiotic relationship between bacteria, diatoms, and the seaweed.

Holobionts are characterized by the relationship between host and their associated organisms such as the biofilm associated with macroalgae. Considering that light is essential to macroalgae survival, the aim of this study was to verify the effect of light on the heterotrophic activity in biofilms of the brown macroalgae Sargassum furcatum during its growth cycle. Measurements of heterotrophic activity were done under natural light levels at different times during a daily cycle and under an artificial extinction of natural light during the afternoon. We also measured Sargassum primary production under these light levels in the afternoon. Both measurements were done with and without photosynthesis inhibitor and antibiotics. Biofilm composition was mainly represented by bacteria but diatoms, cyanobacteria, and other organisms were also common. When a peak of diatom genera was recorded, the heterotrophic activity of the biofilm was higher. Heterotrophic activity was usually highest during the afternoon and the presence of a photosynthesis inhibitor caused an average reduction of 17% but there was no relationship with Sargassum primary production. These results indicate that autotrophic production in the biofilm was reduced by the inhibitor with consequences on bacterial activity. Heterotrophic activity was mainly bacterial and the antibiotics chloramphenicol and penicillin were more effective than streptomycin. We suggest primary producers in the biofilm are more important to increase bacterial activity than the macroalgae itself because of coherence of the peaks of heterotrophic and autotrophic activity in biofilm during the afternoon and the effects of autotrophic inhibitors on heterotrophic activity.

Comparative tests of net mercury methylation potentials, with cultivated and macrophyte-associated periphyton and using stable ((200)HgCl(2) and CH(3)(199)HgCl) and labeled ((203)HgCl(2)) mercury, have been conducted in the Everglades nutrient removal area (Florida, USA) and in a tropical coastal Brazilian lake (RJ, Brazil). More methylmercury was formed by macrophyte-associated (up to 17% of added (203)Hg(II)) than cultivated (up to 1.6%) periphyton and methylmercury formation was lower in periphyton exposed to light (0.2%). High methylation was also observed for samples incubated with stable mercury isotopes (1.5-7.7% of added (200)Hg(II)), confirming the results obtained with labeled mercury. Simultaneous addition of (200)HgCl(2) and CH(3)(199)HgCl indicated that CH(3)(199)HgCl had no inhibitory effect on Hg methylation. The elevated methylation potentials observed in macrophytes, because of their root-associated periphyton, might contribute significantly to the high levels of methylmercury observed in Everglades biota. Comparative mercury methylation tests were also conducted in the water of a stratified temperate lake (Wisconsin, USA). Similar trends were observed for both stable and radioisotopes, with increasing mercury methylation along the depth profile. The highest levels (0.9% (203)Hg(II) and 0.8% (200)Hg(II)) were obtained below the oxic/anoxic boundary, where sulfide starts to increase, probably as a result of the intense activity of sulfate-reducing bacteria in the anoxic layer.