| Summary: | Tese de doutoramento, Biologia (Ecologia), Universidade de Lisboa, Faculdade de Ciências, 2012 The study of phytoplankton dynamics is a fundamental tool in environmental assessment and monitoring, studies of trophic relationships and modeling ecosystems. The present study was a rare opportunity to study two different ecosystems, such as a polar zone, the Antarctic, and a temperate zone influenced by upwelling processes, the Portuguese coast. The main objective of this study was to understand the physical-chemical processes related to the phytoplankton communities’ distribution in these areas. Particularly, the Nazaré submarine canyon region (coast of Portugal) and around the tip of the Antarctic Peninsula, and characterize their communities through pigment analysis (HPLC) and identifying dominant species by microscopy. A great spatial variability in chlorophyll a (Chl a) was observed in the Antarctic Peninsula: highest levels in the vicinity of the James Ross Island (exceeding 7 mg m-3 in 2009), intermediate values (0.5 to 2 mg m-3) in the Bransfield Strait, and the lowest concentrations in the Weddell Sea and Drake Passage (below 0.5 mg m-3). On the other hand, in the region of Nazaré submarine canyon, a clear onshore-offshore gradient was visible: high Chl a concentrations were recorded in the canyon head, near the coast, where values greater than 4 mg m-3 were observed; in contrast, Chl a was relatively low in offshore regions, with values below 0.5 mg m-3. The use of taxonomic tools such as CHEMTAX software allowed efficient quantification of the contribution of different taxonomic groups present to total Chl a (biomass index). This study also showed that the spatial distribution of macronutrients is one of the key factors regulating the distribution of phytoplankton communities in the Nazaré Canyon region, while in the neighboring Antarctic Peninsula, other factors, such as light availability and/or iron distribution, mostly associated with the structure of the water column, determined the spatial ...
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