Advance of the killer crabs

AN ARMY of voracious giant crabs is on the brink of invading the shallow seas off Antarctica, where an array of unique, almost prehistoric sealife has evolved for millions of years without any predators.

Scientists warned yesterday that global warming was raising the temperature of the seas, allowing the crabs to creep ever higher up the slope leading to the continental shelf.

These waters, whose temperature is about freezing point, are home to fish with anti-freeze proteins in their blood along with brittle stars, giant sea spiders, sea snails and other invertebrates. Some, like the snails, have lost their protective armour and spines.

They would be defenceless against the bone-crushing claws of the invading crustaceans.

The crabs are prevented from venturing into waters that are much colder than 1C, because it causes levels of toxic magnesium to build up in their bodies. But, as temperatures rise, magnesium poisoning will became less of a barrier to them.

In the past 50 years, sea surface temperatures off the western Antarctic Peninsula rose by one degree, double the global average, letting the crabs move to the edge of the continental shelf.

Dr Sven Thatje, of the National Oceanography Centre in Southampton, said: "This Antarctic fauna has existed for tens of millions of years without any predators because it is too cold for them.

"The fauna that we see there has evolved its uniqueness because of a lack of predators.

"Now the crabs are virtually on the doorstep of the shallow, colder waters of the Antarctic shelf. If the warming continues, it is likely that in the near future this temperature barrier preventing the invasion of the shallower waters will be lifted.

"Some species will suffer greatly and may even go extinct. The predators coming in is just one feature of climate change; they will also struggle to cope with the warming itself. But I cannot say whether they will eradicate the entire fauna."

Dr Thatje, who gave a presentation at the American Association for the Advancement of Science's annual meeting in Boston, said the situation provided another reason to reduce greenhouse gases and try to prevent global warming.

"Certainly it has to do with values and maintaining the diversity of the environment," he said. "And we have taken them to the brink of extinction not knowing if these species may be useful in pharmaceuticals, for example.

"The message is that global climate change is not only altering the western world, it is reaching the most remote places on earth. This is a warning; we still have a chance to work against this trend in the Antarctic."

The isolation of crustaceans and other creatures in the seas off Antarctica has created a community akin to Arthur Conan Doyle's Lost World. They resemble those once found in the Pala-eozoic era, hundreds of millions of years ago, before the arrival of modern predators throughout most of the world's oceans.

"That would be a tragic loss for biodiversity in one of the last truly wild places on earth," said co-researcher Dr Rich Aronson, from the Dauphin Island Sea Laboratory in Alabama. "Unless we get control of greenhouse-gas emissions, global warming will ruin the marine life in Antarctica and make the world a much sadder, duller place."

RED TIDE RAVAGES NORWAY

THE crabs on the brink of invading Antarctica's coastal waters are related to another crab army currently marching south along the Norwegian coast.

The giant red king crabs have been moving from Russian waters round the northern tip of Norway in their millions, devastating sealife in their path. Though seen as a delicacy, the species has few natural enemies and eats everything from other crabs to cod larvae. It originated in the north Pacific and was introduced to the Barents Sea in 1960 by the Russians – who wanted to create a commercial fishery.