MICROPLANKTON DOMINANT GROUPS DURING THE 2013/2014 AUSTRAL SUMMER IN ADMIRALTY BAY, KING GEORGE ISLAND, WEST ANTARCTIC PENINSULA

e present study presents the variability of the microphytoplankton community taxonomic composition during the austral summer of 2013/2014.To this end, water temperature, salinity, dissolved inorganic nutrients, chlorophyll, and phytoplankton were studied in December 2013 (Early Summer) and February 2014 (Late Summer) at fi ve sampling sites and three depths (surface, 15 m, and near the bottom) in the shallow (~30 m) region of Admiralty Bay (AB).Microphytoplankton abundances in AB during the 2013/2014 austral summer were, on average (4.5 ± 3.0 x 10 3 cells.L -1 ), similar to those observed during the 2009/2010 austral summer, but 10-fold lower than those registered in 2010/2011.Spatially, three regions were considered in AB.An outer region, near Arctwoski Station, showed higher water temperature (0.76ºC), lower phosphate (1.27µM) and nitrogen (16.9µM) concentrations, and higher silicate (59.8µM) concentrations and microplankton densities (5.4 x 10 3 cells.L -1 ) during Late Summer.Phytoplankton cell densities showed a similar order of magnitude between Early and Late Summer, with a maximum value of 1.5 x 10 4 cells.L -1 at Late Summer in the Arctowski region.During Early Summer, dinofl agellates were dominant at Martel and Mackellar Inlets, whereas diatoms were dominant (~70%) in the Arctowski region.During Late Summer, an increasing trend of the contribution of diatoms was also observed from Martel Inlet (~60%) to the Arctowski region (~80%).Our results showed: (i) unusually low average microplankton abundances; (ii) events of dominance of mid-sized diatoms (30-80 µm), e.g., alassiosira antarctica, as observed in February 2014, probably associated with cold coastal water and higher silicate concentrations; and (iii) periods of dominance of small dinofl agellates (< 30µm) of the genera Prorocentrum and Protoperidinium.