CONTRASTING ECOLOGICAL REGIMES OF MICROBIAL PLANKTON ALONG BEAGLE CHANNEL AND BURDWOOD BANK IN SUB-ANTARCTIC WATERS

GUINDER, VALERIA A.; MALITS, ANDREA; FERRONATO, CAROLA; KROCK, BERND; GARZÓN-CARDONA, JOHN; MARTINEZ, ANA MARÍA

Mar del Plata

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

Asociación Latinoamericana de Investigadores en Ciencias del Mar-ALICMAR

Marine microbial plankton hold high structural and functional diversity, however, highresolutiondata are lacking in a large part of the Global Ocean. The Burdwood Bankhosts rich benthic biodiversity in low chlorophyll waters of the southern PatagonianShelf, Argentina. So far, the microorganisms that sustain the productivity over the bankhave not been described. During austral summer 2016, we assessed the microbialplankton (0.2-200 μm cell size) diversity and biomass along a longitudinal transect(54.2-55.3°S, 58-68°W) from the Beagle Channel (BC) to the BB, characterized bycontrasting hydrography. Results displayed a marked zonation in the composition andstructure of the microbial communities. Protistan phytoplankton biomass was 28 timeshigher in the BC than in oceanic waters above the BB, attributed mainly to large diatomblooms. In contrast, over the BB, small coccolithophores such as Emiliania huxleyi,nanoflagellates and phototrophic picoplankton dominated. In turn, the biomass ofmicroheterotrophs above the BB doubled the biomass in the BC due to large ciliatesand dinoflagellates. Notably, toxic phytoplankton species and their associatedphycotoxins were detected, in particular high abundance of Dinophysis acuminata andpectenotoxins above the bank, highlighting their prevalence in open subpolar regions.Picoeukaryotes and Synechococcus were remarkably important over the bank, both atsurface and deep waters. Their biomass surpassed that of phototrophic protists by 5times, emphasizing the importance of small-sized phytoplankton in low chlorophyllwaters. The homogeneous water column and high retention over the bank seem tofavor the development of picophytoplankton and microzooplankton and theirexportation to the benthos. Overall, our findings unfold the plankton configuration in theSouthern Patagonian Shelf, ascribed as a sink for anthropogenic CO2, and highlight thediverse ecological traits that microorganisms develop to adjust their yield to changingconditions.