Fig 1.
Study area at the south of the Argentine Patagonian shelf, SW Atlantic.
In the lower panel, the 29 sampling stations of the BOPD cruise in December 2016 are shown. Bathymetric data: IOC, IHO, and BODC (2003). PO = Pacific Ocean, AO = Atlantic Ocean, TF = Tierra del Fuego, YB = Yaghan Basin, BB = Burdwood Bank. In the temperature-salinity diagram, the acronyms indicate the water masses: Beagle Magellan Water (BMW), Subantarctic Shelf Water (SSW) and Subantarctic Water (SAW).
Fig 2.
Vertical profiles of physical parameters.
Potential temperature (°C), salinity, Brunt Wäisälä parameter of water column stability (cyc h-1) and fluorescence (RFU, relative fluorescence unit). The parameters are shown in two transects: from the Beagle Channel to the eastern Staten Island (left panels, stations 1 to 7) and from the Western Staten Island to the Burdwood Bank (right panels, stations 10 to 28). Stations 8, 9, 17, 18 and 29 are not included in these transects.
Fig 3.
Surface in situ chlorophyll a concentration (μg L-1) and abundance (cells L-1) of microbial plankton > 5μm.
Phytoplankton includes diatoms + flagellates + coccolithophore (Emiliania huxleyi) + phototrophic dinoflagellates (dinoflagellates P). The three bottom panels are heterotrophic protists: ciliates, Mesodinium rubrum (a mixotrophic ciliate which is an obligate prey of the toxic Dinophysis acuminata) and dinoflagellates H.
Fig 4.
Relative abundance (cells L-1, upper panel) and biomass (μg C L-1, lower panel) of planktonic groups (> 5 μm) expressed in % at the sampling stations.
Fig 5.
(A) Cluster analysis based on Bray Curtis similarity index of the microbial plankton > 5 μm, at the study stations during the expedition in the austral summer. The abundance of the species (cells L-1) were transformed using log (x+1). (B) The results of the cluster analysis are shown in the map of the study area.
Fig 6.
Most representative species of phytoplankton > 5 μm responsible of the spatial zonation resulted from SIMPER analysis.
Panels (A) and (B) are diatoms, (C) shows the diatom cf. Shionodiscus gaarderae, the coccolithophore Emiliania huxleyi and nanoflagellates.
Fig 7.
Distribution of picoplankton (in cells L-1) in the surface (A) and in the water column (B).
Fig 8.
Surface biomass (carbon content) of diatoms and picophytoplankon (picoeukaryotes + Synechococcus) along the sampling stations.
The diatom species that contributed most to the biomass in each area are indicated.
Fig 9.
Surface distribution of phycotoxins (circles, in ng NT-1) and the potential planktonic producers (bars, in cells L-1).
AZA-2: azaspiracids, DA: domoic acid and PTX-2: pectenotoxins. Only the stations where toxins were detected are indicated with numbers.
Fig 10.
Normalized averaged densities (cells L-1) of the microbial plankton groups in the three areas depicted with the cluster analysis.
The BC-shelf area includes stations 1 to 10, the transition zone includes stations 11 to 16, and the BB encompasses stations 18 to 29. Green and blue colors correspond to phototrophic and heterotrophic modes, respectively.
Fig 11.
Dominant blooming species and water column structure at station 17.
The photography shows two weakly silicified cells of the small diatom cf. Shionodiscus gaarderae (biovolume: 2828 μm3, carbon content: 181 pg C cell-1), and a cell of the coccolithophore Emiliania huxleyi. Scale bar: 15 μm. In the lower panels, the vertical profiles of water column stability (Brunt-Väisälä parameter, in cyc h-1) and the fluorescence at station 17 are shown.