Spring phytoplankton biomass and hydrography in a productive área of the northern Patagonian shelf and shelf-break

FERRONATO, CAROLA; GUINDER, VALERIA A.; CHIDICHIMO, MARÍA PAZ; LÓPEZ ABBATE, CELESTE; GARZÓN CARDONA, JOHN; MARTINEZ, ANA MARÍA; LARA, RUBÉN

Mar del Plata

Congreso; XVIII Congreso Latinoamericano de Ciencias del Mar COLACMAR 2019; 2019

The Patagonian Shelf hosts one of the most productive marine ecosystems globally. Inparticular, the northern portion of the shelf, ―El Rincón‖ and its frontal areas (38-41°S),constitutes the main spring spawning and feeding habitat for numerous species ofcommercial and ecological interest such as Cynoscion guatucupa (stripped weakfish),Micropogonias furnieri (whitemouth croaker) and Engraulis anchoita (argentineanchovy). Fish larvae actively feed on small copepods and phytoplankton, and hencetheir survival is related to the timing and magnitude of the spring phytoplankton bloom.Since 2013, oceanographic expeditions have been carried out during spring in ElRincón area by the Argentine Institute of Oceanography (IADO-CONICET), under theframework of national financial efforts (i.e. the ―Pampa Azul‖ initiative and institutionalprojects PUE-CONICET). Seawater samples were taken for phytoplanktonquantification and dissolved inorganic nutrients together with temperature and salinityprofiles. Here we used the collected dataset in early spring 2017 to assess themicrobial plankton composition (sizes between 5-200 µm), biomass and trophicregimes across different environmental settings from the coast to the 1000 m isobath.In the coast, diatom abundances were 5 times lower than the average for the sameseason during previous years (2013-2016), but yet the most frequent phytoplanktongroup in the coastal stations. Conversely, nanoflagellates and heterotrophic ciliatesdominated between 50 and 100 m isobaths. In the shelf break, diatoms andphototrophic dinoflagellates dominated. The fluorescence profiles at the shelf showedpeaks of chlorophyll a at 20-25 m depths likely associated to picoplankton production.In addition, potentially toxic species such as Pseudo-nitzschia spp., cf. Azadinium sp.and Prorocentrum cordatum reached high densities in some stations of the shelf andshelf-break. Their prevalence during the productive season draws the attention towardthe possible bioaccumulation of toxins in upper trophic levels and deleterious effects onmarine biota from this socioeconomic important region.