Phytoplankton Assemblages of the Subtropical South West Atlantic: Composition and Dynamics in Relation to Physical and Chemical Processes

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Marine ecosystems respond first to physical-chemical changes in the upper euphotic layers through its phytoplankton community, an assemblage of unicellular eukaryotic and prokaryotic photoautotrophs growing at the same time and spatial scales of hydrodynamic processes. Temporal and spatial environmental changes are followed by physiological adaptations of opportunistic species that dominate the phytoplankton assemblage at a certain time and location. This chapter aims to describe the composition and distribution of the phytoplankton in shelf waters of the subtropical Southwestern Atlantic Ocean, one of the poorly studied areas of the global ocean. It includes regional scale frontal systems caused by thermal upwelling and estuarine plumes together with a variety of meso- and submesoscale hydrodynamic processes that potentially fertilize the euphotic zone and phytoplankton dynamics in shelf systems. Cause-effect relationships of phytoplankton composition and distributional patterns in relation to environmental properties rely on published information which are geographically limited and seasonally fragmented. Nevertheless, the chapter gives a general overview of particular ecological features of the subtropical Brazilian province and its environmental drivers. Despite the recent progress of biomolecular techniques in facilitating taxonomic identification in order to expand the knowledge of phytoplankton dynamics and composition in the South West Atlantic, a joint regional effort is necessary to better understand the baselines of the ecosystem functioning provided by phytoplankton organisms. This will be necessary for modeling future scenarios of regional marine ecosystem services facing the global climatic changes expected in the next decades.