Phytoplankton biomass dynamics and environmental variables around the Rocas Atoll Biological Reserve, South Atlantic

The Rocas Atoll Biological Reserve is located in the Atlantic Ocean, at 3º 51' S and 33º 49' W. It lies 143 nautical miles from the City of Natal, Rio Grande do Norte (Brazil). The purpose of this study was to analyze the hydrology, water masses, currents and chlorophyll a content to determine the dynamics of phytoplankton biomass around the Rocas Atoll. Samples were collected in July 2010 in the area around the Atoll, using the Research Vessel Cruzeiro do Sul of the Brazilian Navy. Two transects were established according to the surface currents, one of which at the southeast of the Atoll (SE) and the other at norwest (NW). Three collection points were determined on each of these transects. Samples were collected at different depths (surface and DCM - Deep Chlorophyll Maximum) and different times (day and night). According to PCA (Principal Component Analysis), the nutrients analyzed, DIN (dissolved inorganic nitrogen), DIP (dissolved inorganic phosphorus) and silicate, were inversely correlated with temperature and dissolved oxygen. Most environmental variables showed a significant increase due to the turbulence on the Northwest transect. There was an increase in the concentration of chlorophyll a and nutrients when the temperature and oxygen in the mixed layer was reduced due to the influence of the SACW (South Atlantic Central Water). Despite the increase observed in some variables such as nutrient salts and chlorophyll a, the temperature in the mixed layer attained a mean value of 23.23 ºC due to the predominance of Tropical Water. The increase of the phytoplankton biomass on the NW transect was, therefore, caused by the "island effect" and not by upwelling.A Reserva Biológica do Atol das Rocas situa-se no Oceano Atlântico, a 3º 51 'S e 33º 49' W, distante 143 milhas náuticas da cidade de Natal, estado do Rio Grande do Norte (Brasil). Este estudo teve como objetivo analisar a hidrologia, massas de água, correntes e o teor de clorofila a para determinar a dinâmica da biomassa fitoplanctônica em torno do Atol das Rocas. As amostras foram coletadas em julho de 2010 na área em torno do atol, usando o navio Oceanográfico da Marinha do Brasil, Cruzeiro do Sul. Dois transectos foram estabelecidos de acordo com a corrente superficial, um transecto em direção sudeste (SE) e o outro, em direção noroeste (NO) do Atol das Rocas. Nestes transectos foram determinados três pontos de coleta para cada um. As amostras foram coletadas em diferentes profundidades (superfície e PMC - Profundidade Máxima de Clorofila) e diferentes períodos do dia (dia e noite). De acordo com a ACP (Análise de Componentes Principais), observou-se que os nutrientes analisados, NID (nitrogênio inorgânico dissolvido), PID (fósforo inorgânico dissolvido) e silicato, correlacionaram-se inversamente com a temperatura e oxigênio dissolvido. A maioria das variáveis ambientais apresentou aumento significativo em função da turbulência no transecto noroeste. Pode-se observar que houve aumento dos teores de clorofila a e nutrientes, e redução da temperatura e oxigênio na camada de mistura em função da influência da ACAS (Água Central do Atlântico Sul). Apesar do aumento observado em algumas variáveis, como sais nutrientes e clorofila a, a temperatura na camada de mistura esteve com valor médio de 23,23 ºC, devido ao predomínio da Água Tropical. Portanto, o aumento de biomassa fitoplanctônica no transecto NW foi provocado pelo "efeito ilha" e não pela ressurgência

O ecossistema recifal de Serrambi (Nordeste do Brasil): biomassa fitoplanctônica e parâmetros hidrológicos.

O ecossistema recifal de Serrambi, situado no litoral sul de Pernambuco, encontra-se constituído por recifes de arenito do tipo franja. A área recifal se destaca pela elevada produtividade, biodiversidade, pesca artesanal e atividades recreativas. Buscando avaliar as condições ambientais, analisou-se a distribuição sazonal e espacial da clorofila a e algumas variáveis ambientais. Foram realizadas coletas em três meses de cada período sazonal, em três pontos de coleta, na superfície, baixa-mar e preamar em maré de sizígia. A maioria dos parâmetros hidrológicos apresenta a diferença sazonal significativa devido a interferência da pluma do rio Sirinhaém, provocando aumento do material em suspensão, nutrientes e diminuindo salinidade, temperatura e transparência. De acordo com a ACP (Análise de Componentes Principais), pluviosidade foi a forçante física que mais interferiu no sistema, correlacionando-se diretamente com material particulado em suspensão, nitrato, silicato, fósforo e nitrito e inversamente com transparência, temperatura e salinidade. A clorofila a variou tanto espacial como sazonalmente (0,35 a 3,34 mg.m-3), havendo maior concentração no período chuvoso e a fração < 20μm (pico e nanoplâncton), foi a que mais contribuiu para a área. Os teores de clorofila a associados à elevada taxa de saturação de oxigênio e baixos teores de nutrientes, indicaram tratar-se de uma área ainda isenta de eutrofização.The reef ecosystem of Serrambi, is situated on the southern coast of Pernambuco, is composed of sandstone reefs of fringe type. In the marine coastal area, the reef stands for its productivity, biodiversity, fisheries and recreational activities. Aiming to evaluate the environmental conditions associated with that ecosystem, the seasonal and spatial distribution of chlorophyll a and some environmental variables were analyzed. Most of the hydrological parameters showed significant seasonal differences due to interference of the plume of the Sirinhaém river during the rainy season, increasing the suspended particles, the concentration of nutrients and reducing salinity, temperature and transparency. According to the PCA (Principal Component Analysis), rainfall was the most important physical forcing that affects the system, correlating directly with suspended particulate matter, nitrate, silicate, phosphate and nitrite and inversely with transparency, temperature and salinity. Chlorophyll a showed both, spatial variation and between seasons (0,35 a 3,34 mg.m-3), with the highest concentration at the rainy season. The fraction ≤ 20μm (pico and nanoplankton) was the largest contributor to the phytoplankton biomass. The chlorophyll a levels associated with the high rate of oxygen saturation and low nutrients concentration, indicated that this is an area free of eutrophication

Phytoplankton biomass dynamics and environmental variables around the Rocas Atoll Biological Reserve, South Atlantic

Abstract The Rocas Atoll Biological Reserve is located in the Atlantic Ocean, at 3º 51' S and 33º 49' W. It lies 143 nautical miles from the City of Natal, Rio Grande do Norte (Brazil). The purpose of this study was to analyze the hydrology, water masses, currents and chlorophyll a content to determine the dynamics of phytoplankton biomass around the Rocas Atoll. Samples were collected in July 2010 in the area around the Atoll, using the Research Vessel Cruzeiro do Sul of the Brazilian Navy. Two transects were established according to the surface currents, one of which at the southeast of the Atoll (SE) and the other at norwest (NW). Three collection points were determined on each of these transects. Samples were collected at different depths (surface and DCM - Deep Chlorophyll Maximum) and different times (day and night). According to PCA (Principal Component Analysis), the nutrients analyzed, DIN (dissolved inorganic nitrogen), DIP (dissolved inorganic phosphorus) and silicate, were inversely correlated with temperature and dissolved oxygen. Most environmental variables showed a significant increase due to the turbulence on the Northwest transect. There was an increase in the concentration of chlorophyll a and nutrients when the temperature and oxygen in the mixed layer was reduced due to the influence of the SACW (South Atlantic Central Water). Despite the increase observed in some variables such as nutrient salts and chlorophyll a, the temperature in the mixed layer attained a mean value of 23.23 ºC due to the predominance of Tropical Water. The increase of the phytoplankton biomass on the NW transect was, therefore, caused by the "island effect" and not by upwelling