The Phytoplankton of the Patagonian Shelf-Break Front

Abstract

Intense phytoplankton blooms in the Patagonian Shelf-Break Front (PSBF) in the southwest Atlantic Ocean (~35 °S–55 °S) are responsible for making this large marine ecosystem one of the most productive and rich in resources and biodiversity of the Global Seas. This systematic review presents up-to-date knowledge of the phytoplankton community composition, biomass and primary productivity along the permanent PSBF from temperate to subpolar latitudes. The interaction between wind stress, shelf waters, the steep slope and western energetic edge currents (i.e. Malvinas and Brazil Currents) originates upwelling areas and phytoplankton outbreaks, with maxima in spring and summer. On a sub-regional scale, the structure of the phytoplankton community is driven by the interplay between the complex geomorphological and hydrographical characteristics across the shelf-to-open ocean transition, also modulated by seasonal changes in light and nutrients. Hence, different assemblages of phytoplankton functional groups and size classes are observed along contrasting areas of the PSBF. Phytoplankton blooms have been studied from field observations in oceanographic cruises, satellite imagery and modelling. As a general outcome, blooms of micro-phytoplankton, e.g. large diatoms and dinoflagellates, are responsible for the high chlorophyll levels in austral spring, while blooms of pico- and nanophytoplankton occur in summer, e.g. blooms of calcified and non-calcified haptophytes such as the coccolithophore Emiliania huxleyi and Phaeocystis antarctica. Potentially toxic phytoplankton and associated phycotoxins have been increasingly documented in the last decade, especially multispecific blooms of dinoflagellates of the genera Azadinium and Amphidoma, producers of azaspiracids (AZAs). The occurrence of these natural hazards raises scientific and social concern about their drivers and impacts on marine resources and human health. This review motivates further discussion on the taxonomical and functional biodiversity of phytoplankton and their biogeochemical roles in the PSBF, which will help to elucidate possible shifts at the base of the food web driven by Global Change that might have repercussions on ecosystem services.