krill

krill, a Norwegian word applied to the stomach contents of the baleen whales killed in the Southern Ocean. The contents weighing several tonnes were almost entirely a single species of plankton, a euphausiid. This shrimplike crustacean (Euphausia superba) is the keystone species in the ecosystem, and is the main food of several whales, seals, penguins, fish, and seabirds. Initially ‘krill’ referred just to E. superba, but is now used generally for any of the 86 species of euphausiid that occur in the plankton of the world's oceans. Many krill species are herbivores, filtering phytoplankton out of the water. In the Southern Ocean the presence of huge swarms of E. superba has led to a fishery developing to catch and process the krill. Commercial exploitation of krill by Russians and Japanese in the Southern Ocean began in 1972, and catches rapidly rose to over half a million tonnes a year. But annual catches have now (2004) fallen for political and logistical reasons to less than a hundred tonnes a year. Any exploitation of living resources in the Southern Ocean is now carefully regulated under the terms of the Antarctic Treaty—an international agreement to maintain Antarctica for exclusively peaceful purposes—to prevent further large-scale damage to the Southern Ocean ecosystem.

Prior to the days of whaling, baleen whales in the Southern Ocean were consuming hundreds of millions of tonnes of krill each year. However, the slowness with which the whale populations have been recovering since the virtual cessation of whaling in 1985 suggests that other species have moved in to exploit the krill resource, and other krill-eating species including penguins and fur seals have undergone population explosions. Krill tends to be most abundant along the ice edge where algal productivity is enhanced by the ice melt. If future climate change alters the seasonal pattern of pack-ice formation and melting, the whole Southern Ocean ecosystem could be at risk.

M. V. Angel