SIZE-FRACTION, TROPHIC CATEGORIES AND MORPHOTYPES STRUCTURE OF PLANKTON SMALLER THAN 20 ¼m DURING THE AUSTRAL SUMMER (ADMIRALTY BAY, KING GEORGE ISLAND, WAP)

Abstract

e density and distribution of plankton community smaller than 20 μm in Admiralty Bay (King George Island, Antarctica) were studied at three sampling sites during the austral summer of 2013/2014 (two surveys at the beginning – early summer, two at the end – late summer). e aim was to identify the environmental factors that in uence their variability. Salinity (34.2 ± 0.1) and temperature (0.47 ± 0.24°C) showed little variation in late summer, but in general, the concentration of dissolved nutrients increased towards this period. Organisms smaller than 10μm showed the higher contribution (74%) for Chlorophyll a concentration. Picoplankton (<2 μm), dominated by basically heterotrophs (98.5%), had density of 3.9 ± 1.8 x108 cell L-1. e fraction between 2 and 20 μm, dominated by autotrophs (60%), presented densities up to 3.6 ± 1.2 x106 cell L-1. is community was dominated by cocci and spherical morphotypes. Our results suggest that: (i) cell density increase along the study period followed nutrient and organic matter inputs; (ii) lower densities relative to 2009-2011 summers were related to lower temperatures and melting rates, besides predation forces, demonstrating the complex spatial-temporal relationships that take place between plankton community and environmental parameters at Admiralty Bay coastal zone.