In the sea ice of the polar oceans, algae and other small organisms are found that can form a food source for other marine animals living underneath the ice. Information on how animals use this food source remains incomplete. Additionally, sea ice has other functions in the life of marine species, for example, as a shelter from predators. In this thesis, the importance of sea ice in the life of animals in both polar regions, such as Antarctic krill and polar cod, was investigated. This was done by looking at distribution, diet and energy content, in relation to certain sea-ice properties. Further knowledge on how polar species utilize the sea ice and how sea ice affects their distribution is necessary to predict the consequences of ongoing climate change. Knowledge on the sea-ice associated food web is, furthermore, important to enable making a fisheries policy that ensures that harvesting a part of the population does not permanently, negatively impact the ecosystem.