A dominant Antarctic ecological paradigm suggests that winter sea ice is the feeding ground for krill larvae. However, several recent observations conflict with this hypothesis. Our study presents the first direct evidence that winter sea ice is actually a food-poor environment when compared to neighbouring open water regions. We found that complex under ice habitats are vital for larval krill, providing shelter from currents. During the day the larvae feed on the sparse ice-associated food but after sunset, they migrate into the water below the ice. This behaviour allows access to more food and promotes the dispersal of larvae to spring feeding grounds. Current larval krill overwintering and nursery habitats in the SW Atlantic are predicted to become ice-free in the future. This will lead to an enhanced food supply and faster larval development and growth but might increase the dispersal of larvae out of the SW Atlantic ecosystem.

Supplement to: Meyer, Bettina; Freier, Ulrich; Grimm, Volker; Groeneveld, Jürgen; Hunt, Brian P V; Kerwath, Sven; King, Rob; Klaas, Christine; Pakhomov, Evgeny A; Melbourne-Thomas, Jess; Murphy, Eugene J; Thorpe, Sally; Stammerjohn, Sharon; Wolf-Gladrow, Dieter A; Auerswald, Lutz; Götz, Albrecht; Halbach, Laura; Jarman, Simon; Kawaguchi, So; Krumpen, Thomas; Meiners, Klaus M; Nehrke, Gernot; Ricker, Robert; Summer, Michael; Teschke, Mathias; Trebilco, Rowan; Yilmaz, Noyan (2017): The winter pack ice zone provides a sheltered but food-poor habitat for larval Antarctic krill. Nature Ecology & Evolution