ever, the sea-ice habitat is of most important for larvae The presence of extensive areas of sea ice is of overrid-
and juvenile stages of the krill species Euphausia su- ing importance to many polar marine mammals. Most
perba. Concentrations up to 3000 individuals per square of the marine mammals that are year-round residents
metre have been observed in under-ice crevices during of the Arctic or the Antarctic spend much of the year in
spring
60
. Sea-ice algae and bacterial assemblages on the close association with sea ice. Predictions for changes in
underside of ice floes enable the krill larvae to survive sea-ice conditions in polar regions due to global warm-
the winter months when food in the water column is ing are a cause for great concern with respect to polar
absent. Sea ice also provides them with an important marine mammal populations. Worst case scenarios cer-
refuge from predators. tainly include the extinction of some species in the com-
ing decades in the Arctic
31,64
.
Mammals and birds dependent on sea ice
Climate change also poses risks to these polar marine
Marine mammals endemic to polar regions have evolved mammals beyond the direct impacts on habitat brought
into specialists that deal extraordinarily well with condi- about by alterations to the physical environment. These
tions that would be considered very harsh for most other include
31,65–67
:
mammals
61–63
. Their morphology, life history and behav- changes to their forage base (such as shifts in the spe-
iour patterns are all finely tuned to deal with cold temper- cies, density and distribution of prey species);
atures and the high degree of variation in temperatures increased competition from temperate species expand-
and conditions between seasons and from year to year. ing northward;
Figure 5.15a: Underside of multi-year sea ice. Figure 5.15b: Gammarus wilkitzkiii, one of the most abundant
Photo: Haakon Hop, Norwegian Polar Institute
ice amphipods associated with under-ice habitats.
Photo: Haakon Hop, Norwegian Polar Institute
82 GLOBAL OUTLOOK FOR ICE AND SNOW