Abstract Primary production is essential in shaping biogeochemical cycles and microbial and ecosystem dynamics. The distribution of chemosynthetic rates in pelagic zones and their participation in the carbon cycle, especially when compared to photosynthetic rates in the Southwestern Atlantic Ocean, are poorly constrained. This study aimed to measure pelagic photo- and chemosynthetic productivity and to analyze their spatial distribution and abiotic drivers. Samples for photosynthesis experiments collected at the surface and deep chlorophyll maximum (DCM) were incubated with 14C-bicarbonate at eight light levels, simulating in situ conditions. Samples for chemosynthesis experiments were collected throughout the water column, from the surface, DCM, 250 m, 900 m, 1,200 m, and 2,300 m, and were incubated in the dark. Rates were analyzed using statistical tests to verify spatial differences between groups of samples and generalized linear models to identify correlations with environmental variables (temperature, salinity, density, mixed layer depth, dissolved oxygen, nitrite, nitrate, silicate, phosphate, turbidity, CDOM, and phycoerythrin and chlorophyll-a concentrations). Moreover, both processes were integrated from the surface to the DCM and compared at the same stations to determine the relative contribution in the epipelagic zone. The photosynthetic and chemosynthetic rates were, on average, 3.00 ± 3.26 mg C m-3 h-1 and 0.97 ± 1.22 mg C m-3 h-1, respectively. In most stations, chemosynthesis represented an average of 10.2% of total primary productivity, but surpassed photosynthesis in three experiments (reaching 63.4 – 78.8%). Photosynthesis displayed a clear offshore-onshore gradient, along with correlated CDOM concentrations, indicating an autochthonous production of the latter. Chemosynthesis, on the other hand, exhibited high variability and lack of prediction by studied environmental variables, with isolated points of substantially higher activity.

Abstract Iron is a limiting nutrient for Symbiodiniaceae (colloquially known as zooxanthellae), with low solubility in seawater. The use of stable, soluble, and chemically defined iron complexes is proposed as a strategy to control the supply of this metal to target organisms. In this work, we investigated the effect of iron(II) and derivatives of iron(III) (desferrioxamine, deferiprone, deferasirox, and HBED) over the growth and metal loading of five Symbiodiniaceae species. Iron supplementation did not affect growth or metal load in species with high iron stocks. In contrast, for species with low iron stocks, hydrophobic Fe(DFX)2 was very efficient in inducing growth and iron loading. Also, the desferrioxamine derivative of iron Fe(DFO) appeared as an interesting, ecologically friendly source of the nutrient. The effect of iron supplementation on the growth of Breviolum minutum submitted to heat shock was also studied. Iron supplementation prior to the heat shock episode increased the heat tolerance of B. minutum. Such findings provide new insights for the strategy of iron supplementation to improve the fitness of Symbiodiniaceae, both in vitro and in the environment.

Variações de curta escala das concentrações de nutrientes, clorofila-a (Cl-a) e séston foram acompanhadas em uma estação fixa no canal de Bertioga (CB), sudeste do Brasil, em dois ciclos completos de maré de quadratura e sizígia, no inverno de 1991. Dados simultâneos da estrutura hidrográfica, marés e correntes permitiram calcular o transporte resultante daquelas propriedades. A advecção por maré e o fluxo de água doce foram as principais forçantes da estrutura hidrográfica e da distribuição de nutrientes e Cl-a. As concentrações médias de NID e fosfato foram altas (respectivamente: 16,88 e 0,98 ¼M na quadratura e 10,18 e 0,77 ¼M na sizígia). Apesar da disponibilidade de N e P, os valores médios de Cl-a foram baixos: 1,13 mg m-3 (na quadratura) e 3,11 mg m-3 (sizígia), sugerindo que a alta taxa de renovação das águas do CB limitam o acúmulo de fitoplâncton. Os maiores valores de Cl-a relacionaram-se à entrada de águas costeiras enquanto que as altas concentrações de nutrientes foram relacionadas às águas salobras. Os nutrientes dissolvidos foram exportados em ambas as marés, séston e Cl-a foram exportados na sizígia e, na quadratura, a Cl-a foi importada. O estudo dos principais componentes do transporte indicou uma susceptibilidade desse sistema à introdução de poluentes oriundos da área costeira, revelando uma potencial fragilidade ambiental.

Short-term variability of nutrients, chlorophyll-a (Chl-a) and seston (TSS) concentrations were followed up at a fixed station in the Bertioga Channel (BC), Southeastern Brazil, over two full tidal cycles of neap and spring tides, during the winter of 1991. Simultaneous data on hydrographic structure, tidal level and currents allowed the computation of the net transport of those properties. Tidal advection and freshwater flow were the main forcing agents on the water column structure, nutrient availability and Chl-a distribution. Dissolved inorganic nitrogen and phosphate average values were high (16.88 and 0.98 ¼M, respectively, at neap tide and 10.18 and 0.77¼M at spring tide). Despite N and P availability, Chl-a average values were low: 1.13 in the neap and 3.11 mg m-3 in the spring tide, suggesting that the renovation rate of BC waters limits phytoplankton accumulation inside the estuary. The highest Chl-a was associated with the entrance of saltier waters, while the high nutrient concentrations were associated with brackish waters. Nutrients were exported on both tides, TSS and Chl-a were exported on the spring tide and Chl-a was imported on the neap tide. The study of the main transport components indicated that this system is susceptible to the occasional introduction of pollutants from the coastal area, thus presenting a facet of potential fragility.

A contribuição dos canais estuarinos de Santos e São Vicente para a eutrofização da baía de Santos foi avaliada quantificando-se o transporte instantâneo de sal, fosfato e nitrogênio inorgânico dissolvido (NID), material em suspensão orgânico (MSO) e inorgânico (MSI) e clorofila-a, durante a estação seca (inverno austral- Agosto/1999) e chuvosa (verão austral- Janeiro/ 2000). As amostragens foram realizadas em períodos de sizígia e quadratura, durante as marés enchentes e vazantes, nas secções transversais das bocas dos canais de São Vicente e Santos. Os valores de transporte instantâneo obtidos durante o período de amostragem indicaram exportação de NID, principalmente sobre a forma de N-NH4 (valor máximo de 1155,1 g s-1) na estação chuvosa; importação de fosfato durante a estação seca (máximo de 385,6 g s-1) e exportação de MSI, MSO e clorofila-a em períodos de maior contribuição fluvial. Estes resultados indicam uma importante contribuição dos canais estuarinos de Santos e São Vicente para a eutrofização da baía de Santos, especialmente durante o período chuvoso.

The contribution of the polluted São Vicente and Santos estuarine channels to the eutrophication of Santos bay was assessed through the quantification of instantaneous transport of salt, dissolved inorganic nitrogen (DIN) and phosphate, organic and inorganic matter (OSM and ISM) and chlorophyll-a (Chl-a), during dry (austral winter- August/ 1999) and rainy (austral summer- January/2000) seasons. Samplings were carried out during spring and neap tides, in flood and ebb phases, in two transversal sections at the mouths of the São Vicente and Santos channels. Instantaneous transport values generally indicated importation of salt to the estuarine channels, exportation of DIN to the bay, mainly as N-NH4, at a maximum rate of 1155.1 g s-1 during the rainy season; importation of phosphate during the dry season (maximum of 385 g s-1) and exportation of ISM, OSM and Chl-a during periods of greater freshwater discharge. These results demonstrate the great contribution made by the Santos and São Vicente estuaries to the eutrophication of Santos bay, especially in the rainy season.

A mistura vertical entre a Água Central do Atlântico Sul (ACAS) e a Água Costeira (AC) foi simulada através de experimentos tipo microcosmos, com o fitoplâncton autóctone (fração < 150 mm) e sem enriquecimentos nutricionais. A ACAS é fria (T< 18°C) e rica em nutrientes, enquanto a AC é mais quente (T> 20°C) e oligotrófica. O potencial trófico dessas águas e de uma mistura equivalente de ambas (ACAS+AC) foi comparado a 100, 30 e 10% da luz solar, sob temperatura da água do mar na superfície, em condições de inverno e verão. Os resultados demonstram a importância da ACAS como agente fertilizador da camada de mistura tanto por introduzir nutrientes, favorecendo a ocorrência de produção nova, como pelo incremento da biomassa fitoplanctônica autóctone ao atingir a zona eufótica. A fase de adaptação observada no inverno foi de 4-5 dias enquanto no verão foi de 1-2 dias. A hipótese da existência de diferenças fisiológicas entre as populações fitoplanctônicas de superfície e fundo em uma coluna de água profunda (80 m) e termicamente homogênea (padrão comum de inverno) foi também testada utilizando microcosmos. Os resultados mostraram que potencial de crescimento fitoplanctônico nas águas de fundo foi significativamente maior que nas de superfície.

The vertical mixing between South Atlantic Central Water (SACW) and Coastal Water (CW) was simulated through microcosm experiments using the autochthonous phytoplankton community (fraction < 150 mm), without nutrient enrichments. SACW is cold (T< 18°C) and nutrient rich, while CW is warmer (T> 20°C) and oligotrophic. The phytoplankton growth potential of SACW, CW and an equivalent mixture of both (SACW+CW) was compared, under 100, 30 and 10% of sunlight, at surface seawater temperature, in winter and summer conditions. Results demonstrate the importance of SACW as a natural eutrophication agent for the mixing layer, allowing the occurrence of new production by nutrient input, and also as a biological seeder through the development of its autochthonous phytoplankton community when it reaches the euphotic zone. The time lag for phytoplankton development during winter was around 4-5 days, against 1-2 days in summer. The hypothesis of physiological differences between surface and bottom phytoplankton populations from a deep (80 m) and thermally homogeneous water column (common winter feature) was also tested through the microcosm experiments. Results obtained clearly demonstrate that bottom water presented higher phytoplankton growth potential than the surface one.

A comunidade planctônica e condições hidrológicas foram avaliadas como parte de um diagnóstico ambiental no Canal de São Sebastião, previamente à construção de um emissário submarino de água de produção, oriunda do terminal marítimo da PETROBRÁS. As amostras foram coletadas em vinte estações oceanográficas situadas na área adjacente ao terminal petrolífero, durante a primavera de 1991. As concentrações de nutrientes inorgânicos dissolvidos e de cIorofila-a obtidas, indicam um ambiente oligo-mesotrófico. Fenóis e sulfetos não foram detectados e os valores de 080, com exceção de três pontos, foram característicos de ambientes não poluídos, apesar da contaminação por óleos e graxas ter sido observada em metade das estações amostradas. O fito e o zooplâncton apresentaram altos índices de diversidade e equitatividade para toda área estudada. O fitoplâncton foi dominado por fitoflagelados, enquanto que o zooplâncton foi dominado por copépodos, especialmente Paracalanus quasimodo. A composição da comunidade planctônica foi similar à de outras áreas adjacentes, sob baixa pressão aotropogênica.

Plankton community and hydrological conditions were assessed as a part of ao environmental diagnosis in São Sebastião Channel, before the building of a submarine outfall of produced water from the oil maritime terminal of PETR08RÁS. Samples were collected in twenty oceanographic stations located in the oil terminal neighboring area, during the springtime of 1991. Oissolved inorganic nutrients and chlorophyll-a concentrations observed indicate an oligo-mesotrophic environment. Phenols and sulfides were absent, 800 values, except for three sampling points, were characteristic of unpolluted environments, although oil and grease were found in half of the sampled stations. Phytoplankton and zooplankton communities presented high diversity and evenness indices for the entire area. Phytoplankton was dominated by phytoflagel1àtes and zooplankton was dominated by copepods, mostly Paracalanus quasimodo. Plankton community composition was similar to that from adjacent regions under low anthropogenic influence.