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Predators such as crabs, rays and even sharks are ready to invade the Antarctic as global warming raises sea temperatures. Their arrival could devastate the continent’s fragile and unique marine ecosystem.

The alien species, armed with bone-crushing jaws and claws against which native species have no defence, are extending their range in the Southern Ocean towards Antarctica’s continental shelf, new research has found.

Because very cold temperatures have kept predators away, some of the world’s most bizarre animal life thrives in Antarctica, including giant sea spiders the size of dinner plates, isopod crustaceans that resemble aquatic woodlice, and sea snails.

As none of these species has evolved alongside swift and voracious predators such as crabs and bony fish, they have few defences against them. The Antarctic’s native fish, which make antifreeze proteins so that their bodily fluids do not freeze, eat small, shrimp-like crustaceans and other soft foods. The main predators on the sea floor are slow-moving sea stars and giant, floppy ribbon-worms.

Research led by Richard Aronson, of the Dauphin Island Sea Lab in Alabama, and Sven Thatje, of the National Oceanography Centre at Southampton, found that warming sea temperatures had allowed crabs to approach closer than ever to the Antarctic continental shelf, suggesting an imminent invasion. The study is also published in the journal Ecology.

Dr Thatje told the Boston conference: “The crabs are on the doorstep. They are sitting in deep water, and only a couple of hundred bathymetric metres now separate them from the slightly cooler shallow water in the Antarctic shelf environment.”

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