The Icelandic Waters ecoregion foodweb is characterized by high primary production. Capelin is a key species in the ecoregion and its lifecycle and migration pattern is an important energy transfer in the ecosystem. Capelin feeds mainly on copepods and euphausiids in waters north of Iceland and then moves to Icelandic waters where it is one of the most important prey for many species, e.g. cod, haddock, saithe, Greenland halibut, seabirds, and marine mammals. Other prey species of lesser importance are shrimp and sandeel. The annual consumption of fish, cephalopods, and crustaceans by cetaceans within the Icelandic Waters ecoregion has been estimated at 6.3 million tonnes.
The foodweb has been affected by changes in hydrography, the capelin fishery, increased immigration of mackerel, and the increasing abundance of large baleen whales. Unlike capelin, mackerel feeds in the ecoregion and are a minor prey item, thereby exporting energy from the system.