Microphytoplankton assemblages in shallow waters at Admiralty Bay (King George Island, Antarctica) during the summer 2002-2003

Microphytoplankton populations were studied in shallow coastal water (< 60 m) near the Brazilian Antarctic Station Comandante Ferraz (EACF) and three reference areas in Admiralty Bay in early and late summer (2002-2003). Phytoplankton was diverse (113 taxa), but not abundant (10(3) cells l(-1)). The highest abundances (> 10(4) cells l(-1)) were caused by pennate benthic diatoms (Fragilaria striatula Lyngbye) that occurred mainly in early summer, associated with the presence of ice. In late summer, when the water temperature (-0.4 to 1.5 degrees C), salinity (34 to 35), and phosphate (2.6 to 4.5 mu mol l(-1)) were highest and the dissolved oxygen was lowest (6.4 to 2.9 ml l-1), centric diatoms (Thalassiosira spp.) were more abundant, suggesting an influence of oceanic waters. Phytoplankton abundance (<= 10(2) cells l(-1)) and chlorophyll a concentrations (0.22 mu g l(-1)) were lowest close to EACF. Pennate diatoms were dominant close to shore and in surface waters elsewhere, probably because of ice melting or sediment resuspension caused by water mixing.