Wednesday, September 14, 2011

503. Climate Change: Giant Red Crabs Invade the Antarctic Abyss

By Andy Goghlan, New Scientist, September 7, 2011

Huge crabs more than a metre across have invaded the Antarctic abyss, wiped out the local wildlife and now threaten to ruin ecosystems that have evolved over 14 million years.
Three years ago, researchers predicted that as the deep waters of the Southern Ocean warmed, king crabs would invade Antarctica within 100 years.
But video taken by a remotely operated submersible shows that more than a million Neolithodes yaldwyni have already colonised Palmer Deep, a basin that forms a hollow in the Antarctic Peninsula continental shelf.
They are laying waste to the landscape. Video footage taken by the submersible shows how the crabs prod, probe, gash and puncture delicate sediments with the tips of their long legs. "This is likely to alter sediment processes, such as the rate at which organic matter is buried, which will affect the diversity of animal communities living in the sediments," says Craig Smith of the University of Hawaii at Manoa, whose team discovered the scarlet invaders.
Hungry invaders
The crabs also appear to have a voracious appetite. Echinoderms – sea urchins, sea lilies, sea cucumbers, starfish and brittle stars – have vanished from occupied areas, and the number of species in colonised areas is just a quarter of that in areas that have escaped the invasion.
"[Echinoderms] constitute a significant proportion of the large animals on the seafloor in many Antarctic shelf habitats," says Smith.
The crabs come from further north and moved in as Antarctic waters have warmed, probably swept into Palmer Deep as larvae in warm ocean currents. They now occupy the deepest regions of Palmer Deep, between 1400 and 950 metres. In 1982, the minimum temperature there was 1.2 °C – too cold for king crabs – but by last year it had risen to a balmier 1.47 °C.
Melting ice sheets tend to make shallower waters in Antarctica cooler than deeper ones. There were no king crabs at depths of 850 metres or less, suggesting that these waters are still too cold for them. But with waters warming so rapidly, they could spread to regions as shallow as 400 metres within as little as 20 years, says Smith.
"Several years ago, my colleagues and I predicted that warming sea temperatures off the west Antarctic Peninsula would allow predatory sea crabs to invade and disrupt the completely unique marine bottom fauna," says Richard Aronson of the Florida Institute of Technology in Melbourne.
"Craig Smith and his team have now discovered a population in a deep basin gouged into the continental shelf off the western peninsula," says Aronson. "What's exciting, new and a bit scary about their find is that somehow, the crabs had to get from the deep sea over part of the continental shelf and then into the basin that is the Palmer Deep."
"That means they're close to being able to invade habitats on the continental shelf proper, and if they do the crabs will probably have a radical impact on the bottom communities."
The best long-term solution? To slow the rate of global warming, says Smith.

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