Declining abundance and shifting distribution for Antarctic krill, Euphausia superba, in the western Antarctic Peninsula

Sammanfattning: Antarctic krill, Euphausia superba, a polar ocean specialist, thrives in the Antarctic severe physical conditions. The krill life cycle consists of strategies that have enabled and supported the species’ dominance of the Antarctic Ocean. Sea Ice extent and duration creates condition that are crucial for survival of the Furcilia larvae. The species has flexibility to food resources and is omnivorous, i.e. are feeding on phyto- and zooplankton. Krill are stenothermal, has a have narrow interval for temperature tolerance. The development from egg to juvenile has several critical phases. One of the first feeding phases, Furcilia, is reliant on winter sea ice for the larval growth, development and survival, at least in the younger stages. The ice provides shelter and substrate for grazing of under sea ice food resources. The Antarctic krill is a key species, an “ecosystem engineer” functioning as the basic food resource for many marine such as vertebrates as fishes, birds, seals, and whales. The krill also makes an important contribution to the world food production. The Antarctic climate and periodic variation in winds, temperatures and circumpolar currents rules the variations in the physical conditions and influence krill food resources and habitat. Global warming changes the preconditions for krill. The Sea Surface Temperature (SST) increases and the Antarctic total ice sheet mass lose volume every year. In the Sea southwest of the Antarctic Peninsula do the Sea ice extent and duration decline in February and in autumn due to the global warming. Diminishing nursery hot spots in these regions will change krill living conditions and influence reproduction cycle, which may lead to a krill populations collapse. The decline of winter Sea ice extent and duration the previous winter is significantly correlated with reduced ice algae food. The krill numerical densities have probably declined sharply in their northern limit since 1970, which is the area supporting the maximum growth of the largest Furcilia stages. The krill population distribution is likely to shift southwards from their past centre in the southwest Atlantic Ocean. In a high emission scenario the krill larvae habitat can be reduced by as much as 80% due to future global warming.