A keystone prey species in the Southern Ocean is retreating towards the Antarctic because of climate change. Krill are small, shrimp-like creatures that swarm in vast numbers and form a major part of the diets of whales, penguins, seabirds, seals and fish. Scientists say warming conditions in recent decades have led to the krill contracting pole-ward.
Antarctic krill are usually less than 6 cm in length, but their size belies the major role they play in sustaining much of the life in the Southern Ocean. They are the primary food source for many species of whales, seals, penguins and fish.