These authors have contributed equally to this work.The Southern Ocean is currently subject to intense investigations, mainly related to its importance for global biogeochemical cycles and its alarming rate of warming in response to climate change. Microbes play an essential role in the functioning of this ecosystem and are the main drivers of the biogeochemical cycling of elements. Yet, the diversity and abundance of microorganisms in this system remain poorly studied, in particular with regards to changes along environmental gradients. Here, we used amplicon sequencing of 16S rRNA gene tags using primers covering both Bacteria and Archaea to assess the composition and diversity of the microbial communities from four sampling depths (surface, the maximum and minimum of the oxygen concentration, and near the seafloor) at 10 oceanographic stations located in Bransfield Strait [northwest of the Antarctic Peninsula (AP)] and near the sea ice edge (north of the AP). Samples collected near the seafloor and at the oxygen minimum exhibited a higher diversity than those from the surface and oxygen maximum for both bacterial and archaeal communities. The main taxonomic groups identified below 100 m were Thaumarchaeota, Euryarchaeota and Proteobacteria (Gamma-, Delta-, Beta-, and Alphaproteobacteria), whereas in the mixed layer above 100 m Bacteroidetes and Proteobacteria (mainly Alpha-and Gammaproteobacteria) were found to be dominant. A combination of environmental factors seems to influence the microbial community composition. Our results help to understand how the dynamic seascape of the Southern Ocean shapes the microbial community composition and set a baseline for upcoming studies to evaluate the response of this ecosystem to future changes.
We describe the phytoplankton community and biomass during a summer coccolithophorid bloom sampled over the Patagonian shelf (48.58S-50.58S). Those phytoplankton species can contribute to the flux of calcium carbonate out of surface waters. Results from both microscope and high-performance liquid chromatography (HPLC) analysis are shown to complement information on the phytoplankton community. From CHEMTAX analysis of HPLC data, the most important organisms and groups identified were the coccolithophorid Emiliania huxleyi, the haptophyte Phaeocystis antarctica, dinoflagellates, diatoms, cryptophytes, prasinophytes and cyanobacteria. Phytoplankton microscope counts were converted into phytoplankton group-specific biovolume estimates. Although some microscope-identified taxa could not be determined by CHEMTAX, e.g. the autotrophic ciliate Myrionecta rubra, cluster analyses from both techniques showed similar results for the main groups. Both Emiliania huxleyi cell concentration and biomass, and the pigment 19 ′ -hexanoyloxyfucoxanthin were the most important biological features during the sampling period. At surface, nitrate was moderately high (0.2 -4.2 mM) in coccolithophorid-dominated samples, whereas phosphate (,0.33 mM) and silicate (,1.35 mM) concentrations were low. Among the environmental factors low Si:N ratios were mainly associated with the dominance of E. huxleyi. Competition and probably differential grazing could also promote a coccolithophorid outgrowth over other photoautotrophs during the summer season in the Patagonian shelf.
A B S T R A C TEstuaries are extremely dynamic environments that are vulnerable to anthropogenic alterations. Thus, monitoring phytoplankton abundances and composition is an essential tool for the prediction of eutrophication and its effects on coastal ecosystems. Phytoplankton biomass, as chlorophyll-a, in the São Vicente estuary (Brazil) varies in response to tidal cycles and seasonal rainfall. Objectives. To present two datasets designed to assess the relationship between chlorophyll-a and changes in water turbidity driven by tide and rain. Methods. Weekly observations were made in the shallow embayment (February to September 2008; site 1) and observations recorded on alternate days (summer 2010, site 2). Results. At site 1, turbidity differed between high and low tides, but on most days was over 3000 RU, maintaining moderate chlorophyll-a levels (4 mg.m -3 ) and only two blooms developed during low turbidity. Site 2 mean turbidity was 1500 RU, nutrient level was higher during neap tides and phytoplankton blooms were mainly observed at the end of neap tides at 15-day intervals, dominated by chain-forming diatoms and occasionally flagellates and pennate diatoms. Conclusions. Taxonomic composition of the blooms was different and their frequency altered by events characterized by intense freshwater discharges from the Henry Borden Hydroelectric Dam (> 9*106.m 3 ), inhibiting phytoplankton accumulation during neap tide periods.
R E S U M OEstuários são ambientes dinâmicos e susceptíveis a alterações antropogênicas. Nesses ambientes, torna-se imprescindível monitoramento do fitoplâncton na previsão da eutrofização e de seus efeitos para o ecossistema. No estuário de São Vicente (Brasil) a biomassa fitoplanctônica, como clorofila-a, varia sazonalmente em resposta às chuvas e marés. O presente estudo visa apresentar dois programas de monitoramento para detectar florações fitoplanctônicas em relação a turbidez da água guiada pelas marés e chuvas. Métodos. As observações foram semanais na porção rasa (Fevereiro a Setembro de 2008; área 1) e observações em dias alternados no canal (verão de 2010; área 2). Os resultados mostram que a área 1, turbidez acima de 3000 RU manteve níveis de clorofila-a médios (4 mg.m -3 ) e duas florações ocorreram apenas em baixa turbidez, sendo esta diferente entre marés alta e baixa. Na área 2, a turbidez manteve-se entre 1500 RU, os nutrientes foram maiores durante as marés de quadratura, e as florações tiveram frequência de aproximadamente 15 dias, no final da quadratura, predominando diatomáceas em cadeia e eventualmente flagelados e diatomáceas penadas. A composição taxonômica variou entre florações e o padrão quinzenal foi significativamente alterado durante eventos com alta descarga de água doce oriundos da usina hidroelétrica Henry Borden (> 9*106.m 3 ) o que impediu o acúmulo de fitoplâncton no período das quadraturas.
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