Spring phytoplankton biomass and hydrography in a productive area of the Northern Patagonian Shelf and Shelf Break

CHIDICHIMO, M. P.; MARTINEZ, A. ; FERRONATO, C.; LOPEZ ABBATE, M. C.; LARA, R.; GUINDER, V.; GARZÓN CARDONA, J.E.

Mar del Plata

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

Asociación Latinoamericana de Investigadores en Ciencias del Mar (ALICMAR)

Microbial plankton community is the base of pelagic food webs and their high structural and functional diversity at spatio- temporal scales, motivates the construction of high-resolution datasets. The Patagonian Shelf hosts one of the most productive marine ecosystems globally. In particular, 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 of commercial and ecological interest such as Cynoscion guatucupa (stripped weakfish), Micropogonias furnieri (whitemouth croaker) and Engraulis anchoita (argentine anchovy). Fish larvae actively feed on small copepods and phytoplankton, and hence their survival is related to the timing and magnitude of the spring phytoplankton bloom. Since 2013, oceanographic expeditions have been carried out during spring in El Rincón area by the Argentine Institute of Oceanography (IADO-CONICET), under the framework of national financial efforts (i.e. the ?Pampa Azul? initiative and institutional projects PUE-CONICET). Seawater samples were taken for phytoplankton quantification and dissolved inorganic nutrients together with temperature and salinity profiles. Here we used the collected dataset in early spring 2017 to assess the microbial plankton composition (sizes between 5-200 µm), biomass and trophic regimes 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 same season during previous years (2013-2016). Conversely, nanoflagellates and ciliates dominated between 50 and 100 m isobath. The fluorescence profiles at the shelf showed peaks 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 and shelf-break. Their prevalence during the productive season draws the attention toward the possible bioaccumulation of toxins in upper trophic levels and deleterious effects on marine biota from this socioeconomic important region.