Climate change and zooplankton dominance in the Antarctic marine ecosystem: implications for the food web

There is a growing body of evidence that the climate of the Antarctic Peninsula region has been warming over the past 40 years with an associated decreased frequency of winters with extensive sea-ice development. These trends potentially will have a major impact on the structure and function of the Antarctic marine ecosystem. In the Antarctic Peninsula region winter sea-ice coverage is a major factor regulating recruitment and population size of Antarctic krill (Euphausia superba) and population dynamics of salps (Salpa thompsoni). Strong krill recruitment success there follows years of extensive winter sea-ice development and large summertime salp blooms follow winters with relatively little sea-ice. An order of magnitude decrease of krill population size, increased incidence of massive salp blooms, and decreased abundance of krill-dependent Adelie penguins (Pygoscelis adeliae) in the past 15 years suggests that the food web may be affected by climate change. The 1994/95 austral summer season followed the first prolonged winter sea-ice season in three years and provides a strong contrast to the previous years which had little or no winter sea-ice development. The hypothesized relationships between krill and salp population dynamics and winter sea-ice conditions are confirmed and the relative importance of krill and salps within the Antarctic food web are assessed here.