Microbial plankton configuration in the epipelagic realm from the Beagle Channel to the Burdwood Bank, a Marine Protected Area in Sub-Antarctic waters

GUINDER V. A.; MALITS A.; FERRONATO C.; KROCK B.; GARZÓN-CARDONA, J.E.; MARTINEZ A

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2020

1932-6203

Marine microbial plankton hold high structural and functional diversity, however, high resolution data are lacking in a large part of the Global Ocean, such as in subpolarareas of the SW Atlantic. The Burdwood Bank (BB) is a submerged plateau (averagedepth 100 m) that constitutes the westernmost segment of the North Scotia Ridge(54°?55°S; 56°?62°W). The BB hosts rich benthic biodiversity in low chlorophyll watersof the southern Patagonian Shelf, Argentina, declared Namuncurá Marine ProtectedArea (NMPA) in 2013. So far, the pelagic microorganisms above the bank have notbeen described. During austral summer 2016, we assessed the microbial plankton(0.2-200 μm cell size) biomass and their taxonomical and functional diversity along alongitudinal transect (54.2-55.3°S, 58-68°W) from the Beagle Channel (BC) to the BB,characterized by contrasting hydrography. Results displayed a marked zonation in thecomposition and structure of the microbial communities. The biomass of phytoplankton>5 μm was 28 times higher in the BC, attributed mainly to large diatom blooms, than inoceanic waters above the BB, where the small coccolithophore Emiliania huxleyi andflagellates <10 μm dominated. In turn, the biomass of microheterotrophs above the BBdoubled the biomass in the BC due to large ciliates. Notably, toxic phytoplanktonspecies and their phycotoxins were detected, in particular high abundance ofDinophysis acuminata and pectenotoxins above the bank, highlighting their presencein open subpolar regions. Picophytoplankton (<2 μm), including Synechococcus andpicoeukaryotes, were remarkably important above the BB, both at surface and deepwaters (up to 150 m). Their biomass surpassed by 5 times that of phytoplankton > 5μm, emphasizing the importance of small-sized phytoplankton in low chlorophyllwaters. The homogeneous water column and high retention above the bank seem tofavor the development of abundant picophytoplankton and microzooplanktoncommunities. Overall, our findings unfold the plankton configuration in the SouthernPatagonian Shelf, ascribed as a sink for anthropogenic CO2, and highlight thediverse ecological traits that microorganisms develop to adjust their yield to changingconditions.