Frozen desert alive : the role of sea ice for pelagic macrofauna and its predators : implications for the Antarctic park-ice food web

In spite of its harsh climate, the Antarctic Seasonal Sea Ice Zone (SIZ) is remarkably diverse and hosts globally significant fisheries resources, such as the Antarctic krill (Euphausia superba). The species community of the ice-water interface layer is assumed to be fundamental to the food web of the Antarctic SIZ. A novel sampling device was developed to investigate this barely accessible community, the Surface and Under Ice Trawl (SUIT). Investigations with SUIT yielded the first large-scale evidence that life under Antarctic pack-ice is surprisingly diverse and abundant. Especially Antarctic krill was closely associated with the underside of sea ice. Comparison with deeper-fishing nets indicated that krill often concentrate closely under ice floes and are less abundant in the water column. Thus, the midwater sampling usually applied for krill stock estimates probably under-estimates the abundance of krill in pack-ice. The importance of sea ice also for large animals was highlighted by a penguin and seal survey finding that the distribution of crabeater seals (Lobodon carcinophaga) was closely related to ice thickness and ocean depth. Furthermore, investigations on the energy content and distribution of fishes in offshore waters suggested that certain fishes can be equally important to krill in the food web of the Antarctic SIZ. These results challenge the classic krill-centered concept of the Antarctic food web. These findings can help to better estimate the response of Antarctic marine ecosystems to changing sea ice characteristics caused by global warming and are relevant for fisheries management and conservation in Antarctica.