When the sea ice melts, juvenile polar cod may go hungry

Biologists confirm how heavily the fish depend on ice algae

Date: March 15, 2017

Source: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

Polar cod fulfil a key role in the Arctic food web, as they are a major source of food for seals, whales and seabirds alike. But the polar cod themselves might soon be the hungry ones. Under the ice of the central Arctic, the juvenile fish are indirectly but heavily dependent on ice algae. As a result, retreating sea ice could have far-reaching impacts on the food web. Though researchers have long since suspected this relation existed, an international team of researchers led by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have now successfully confirmed it.

Arctic sea ice offers a veritable nursery ground for polar cod: young fish between one and two years old live in cracks and crevices under the ice. They drift along with the ice, which is most likely how they make their way from their spawning grounds in the waters of northern Siberia to the central Arctic. During their journey, the young polar cod feed on amphipod crustaceans, which in turn feed on ice algae. As such, there is a direct relation between the polar cod and the ice algae, which could ultimately threaten the young polar cod's survival. This was the key outcome of a study recently published in the journal "Progress in Oceanography." Amongst others, the research institute Wageningen Marine Research in the Netherlands joined in the study.

"Generally speaking, our findings indicate that polar cod are heavily dependent on ice algae," says first author and AWI biologist Doreen Kohlbach. "That means the rapid retreat of Arctic sea ice poses an especially serious threat for polar cod. When the ice retreats, it takes with it the basis of their diet. Given the polar cod's pivotal role, this could also produce changes throughout the entire food web."

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