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.
Onwards
"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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