BioEd Online

The creatures living in Antarctic oceans are accustomed to being cold. But even they barely survived the extra-frigid temperatures of the last ice age, a new study suggests.

At the peak of the last ice age, around 18,000 years ago, seals, birds and other polar animals would have had to eke out an existence around a few clearings — called polynyas — in the sea ice, says Sven Thatje, a polar biologist at the National Oceanography Centre in Southampton, UK. The small openings would have served as year-round oases for algae to grow and form the basis of a food chain supporting fish, birds, seals and whales.

At that time, the permanent sea ice that rings Antarctica would have reached much farther north than it does today — extending up to almost 45 degrees south latitude in the winter. Things were so cold that even some species of penguin had to move as far north as Argentina, in order to survive.

This was despite the fact that some Antarctic creatures have extreme physiological adaptations to help them weather the cold — some fish, for example, have natural antifreeze flowing in their blood.

Thatje presented his work — which rounds up emerging theories on how polar animals specifically adapted to changing climate conditions in the past — in Boston on 15 February, at the annual meeting of the American Association for the Advancement of Science. It also appears in the journal Ecology¹.

Invasion of the killer crabs

Rising ocean temperatures, driven by rising carbon dioxide levels in the atmosphere, are expected to hammer such sea animals in the future. These marine communities have almost no capacity to deal with warming waters — particularly when invading species show up.

Warm-water creatures are already moving into areas once occupied exclusively by polar animals. King crabs, for instance, were spotted last year in the deep waters off the Antarctic Peninsula, where waters are slightly warmer than at the surface thanks to deep-sea currents. As the climate warms, these crabs are expected to move up into areas now hosting pristine, defenseless Antarctic communities. Temperatures along the peninsula have already risen by 1 to 2 degrees Celsius during the past half-century.

"This is the last stand for pristine marine communities," says Richard Aronson, a marine ecologist at the Dauphin Island Sea Lab on Dauphin Island, Alabama.

Sharks could also soon be on the scene, says Cheryl Wilga, a biologist at the University of Rhode Island in Kingston. Currently, Antarctic oceans are so cold that the metabolism of sharks simply can't deal with the physiological demands. But if the oceans warm by another couple of degrees, she says, sharks would be able to move even farther south, into the waters ringing Antarctica.

"Predators will find a veritable smorgasbord waiting for them," says Wilga.