Polar ecosystems thrive significantly on carbon synthesized by sea ice-associated microalgae during long periods of the year. Continued alterations of the sea ice system might not only have dramatic consequences for the sympagic (ice-associated) ecosystem, but will also have a large impact on the pelagic food web due to the close connectivity between the sea ice and the pelagic system. Thus, it is crucial to identify to which extent ecologically important species in the Arctic Ocean trophically depend on ice algae-produced carbon versus carbon produced by pelagic phytoplankton.