luni, 15 septembrie 2008

Antarctic Warming Creating Predator 'Smorgasbord'

Headed South?

- Global warming is setting the stage for an invasion of predators on the sea floor around Antarctica, the likes of which have not been there for more than 40 million years.

Back in the late Eocene epoch, predatory animals such as sharks and crabs were driven away from Antarctic depths when the continent and its surrounding waters turned into an icebox, said researchers on Friday at a symposium at the meeting of the American Association for the Advancement of Science in Boston.

The result was a virtually predator-free zone on the seafloor and a paradise for worms, sea lilies, clams, brittle stars and other bottom-dwelling animals.

All that is about to end, however. Global warming is now raising water temperatures to the point where, very soon, those long-exiled predators could return and wreak havoc on the ocean floor, say biologists.

"It's going to be a smorgasbord," said researcher Cheryl Wilga of the University of Rhode Island. She studies the metabolic limitations of sharks that have kept them from Antarctic waters for millions of years, but may not do so much longer.

"The species in the Antarctic (seafloor) have no defense for shell-crushing predators," said extreme species researcher Brad Seibel, also of the University of Rhode Island. "I don't think that anyone was really aware of this issue."

Along the Antarctic Peninsula, the northernmost, warmest part of the continent, global warming is raising air temperatures quickly. Water temperatures have been warming as well, at a rate of about 0.04 degrees Celsius per year, Wilga says. That comes to about one degree per 25 years.

Compared to the relative stability seen for tens of millions of years, that's incredibly fast. Already, crabs are showing up, and some sharks are poised to pounce once the thermal dinner bell rings.

Antarctic King Crab?

The first exiled predator to return to Antarctica is the king crab. The leggy crustaceans have been found way down on the deep slopes off the Antarctic continental shelf -- where the water is slightly warmer than elsewhere.

There they are fighting the cold, explained marine scientist Richard Aronson of Dauphin Island Sea Lab and the University of South Alabama.

The frigid water makes it hard for the crabs to efficiently flush magnesium out of their bodies, said Aronson. Too much magnesium acts like a narcotic on a crab.

"When it's too cold, the magnesium makes them pass out and die," Aronson said. That's probably why the crabs have been absent for eons. Now, however, in those slightly warmer depths off the continental shelf, it's just warm enough for the crabs to survive there.

As the upper waters continue to warm, nothing will stop the king crabs from moving up onto the continental shelf and feasting. That will "hammer" the old seafloor communities, Aronson said.

"We expect the populations (of seafloor invertebrates) to take a dive," said Aronson.

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