Characterization of the Western Antarctic Peninsula Ecosystem: Environmental Controls on the Zooplankton Community

The zooplankton community of Marguerite Bay, western Antarctic Peninsula, was investigated in relation to variability in chlorophyll concentrations and sea ice dynamics, using a combination of satellite remote sensing techniques and plankton net data. SeaWiFS chlorophyll data were validated with concurrent in situ data measured by HPLC and fluoromentric methods, and results indicate that SeaWiFS chlorophyll is an accurate measure of in situ values when HPLC data are used as ground truth. Climatology data of SeaWiFS chlorophyll west of the Antarctic Peninsula showed that the Bellingshausen Sea and Marguerite Bay usually had higher and more persistent chlorophyll concentrations compared with northern regions. These predictable phytoplankton blooms could provide the Antarctic krill, Euphausia superba, with the food required for successful reproduction and larval survival. Unusually high krill reproduction in 2000/2001 was coincident with above-average chlorophyll concentrations throughout the study area and was followed by the largest juvenile recruitment since 1981. High larval densities at the shelf break along the Antarctic Peninsula may have resulted, in part, from krill spawning in the Bellingshausen Sea. Interannual differences in sea ice also probably contributed to the variability in larval krill abundances. Interannual differences were observed in the species composition of the zooplankton of Marguerite Bay during fall, and these were linked to variability in the environmental conditions. Thysanoessa macrura was the most abundant euphausiid in 2001, while Euphausia crystallorophias dominated in 2002, and E. superba had intermediate densities during both years. Copepods were more abundant in 2001 by a factor of 2.6. Copepods and T. macrura showed a rapid population response to unusually high chlorophyll concentrations in the Bellingshausen Sea and Marguerite Bay during spring-summer 2000/2001, whereas E. superba and E. crystallorophias had a longer term response and showed increased recruitment in fall 2002. There were no clear associations between the distribution of zooplankton and environmental conditions in fall; however there was a significant relationship between chlorophyll concentrations in the Bellingshausen Sea during the preceding spring and zooplankton patterns during fall