Credit: Daniel J Cox/Getty

Even creatures living many metres below the Arctic Ocean's surface rely on algae that grow in sea ice and so, like those living near the surface, may feel the negative effects of shrinking ice.

A team led by Doreen Kohlbach of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, collected small crustaceans and other animals at different depths in the central Arctic Ocean and analysed their fatty-acid content to identify the source of carbon in their diets. Organisms living at the water–ice interface (such as Apherusa glacialis; pictured) got as much as 92% of their carbon from the ice algae. But creatures sampled at up to 50 metres below the surface got 14–55% of their carbon from the algae.

Melting sea ice means a shrinking habitat for algae, which could lead to decreased nourishment for the entire Arctic food web.

Limnol. Oceanogr. http://doi.org/bmtq (2016)