Friday, September 09, 2011
Writing in the journal Proceedings B, scientists report a large, reproductive population of crabs in the Palmer Deep, a basin cut in the continental shelf.
They suggest the crabs were washed in during an upsurge of warmer water.
The crabs are voracious crushers of sea floor animals and will probably change the ecosystem profoundly if and when they spread further, researchers warn.
Related species have been found around islands off the Antarctic Peninsula and on the outer edge of the continental shelf.
But here the crabs (Neolithodes yaldwyni) are living and reproducing in abundance right on the edge of the continent itself.
Judging by the density of the crabs and their tracks, the scientists estimate there may be 1.5 million crabs in the basin.
A female crab retrieved from the area was found to be carrying mature eggs and larvae.
"Our best guess is there was an event, or maybe more than one, where warmer water flushed up across the shelf and carried some of the larvae into the basin," said project leader Craig Smith from the University of Hawaii.
It is believed that this species cannot tolerate water colder than 1.4C.
The seas here get warmer as you descend; and the crabs were only found below 850m.
The researchers calculate that they have probably been there only for 30-40 years; before that, the water would have been too cold even at the bottom of the Palmer Deep.
They cannot as yet survive on the continental shelf, which is at a depth of about 500m; but that could change.
"If you look at the rate at which the seas are warming, (the continental shelf) should be above 1.4C within a couple of decades, so the crabs are likely then to come into shallower waters," Professor Smith told BBC News.
With a legspan of up to a metre, the animals are generally top predators in the seafloor ecosystem.