Plankton structure a in shallow coastal zone at Admiralty Bay, King George Island, West ­Antarctic Peninsula (WAP): pico, nano and ­microplankton and chlorophyll biomass

Abstract

The phytoplankton composition and biomass are being monitored in Admiralty Bay, Antarctic Peninsula since 2002 to detect possible interannual changes on a long-term perspective. In this report, we present the preliminary results of the 2009/2010 monitoring program regarding phytoplankton size-structure and biomass. Even if mean microplankton densities were similar between December 2009 and February 2010, diferent phytoplankton groups dominated each sampling period. Pennate diatoms showed highest contribution in December, whereas athecate dinoflagellates were the most abundant microplanktonic group in February. Pico and nanoplankton were only detailed during the second sampling period, and results showed that phytoplankton were dominated by cells <10 μm (~104 and 107 cells.L–1, respectively). The shift in phytoplankton structure pointed out by the dominance of picoand nano-size cells in phytoplankton and heterotrophic dinoflagellates in late summer must be confirmed by continuing the long-term monitoring program and the implementation of microvariation sampling effort to identify the factors that are actually influencing phytoplankton populations in this environment.