venerdì 9 settembre 2011

Crab Invasion from Antarctica?

King crabs and other crushing predators are thought to have been absent from cold Antarctic shelf waters for millions of years. Scientists speculate that the long absence of crushing predators has allowed the evolution of a unique Antarctic seafloor fauna with little resistance to predatory crabs. A recent study by researchers from the University of Hawaii at Mānoa, Duke University, Ghent University, Lamont-Doherty Earth Observatory, and Hamilton College, indicates that one species of king crab has moved 120 km across the continental shelf in West Antarctica and established a large, reproductive population in the Palmer Deep along the west Antarctic Peninsula. King crabs, also called stone crabs, are a superfamily of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food, the most common being the red king crab. The worrisome intruder is a bright-red deep-sea predator that previously had been spotted only in the Ross Sea, on the other side of West Antarctica. The study's robot camera, viewed over 1.2 miles, spotted 42 crabs, all of them at depths lower than 2,760 feet, where the water was a relatively balmy 34.5 degrees Fahrenheit. "This is a very interesting discovery for several reasons," said Craig Smith, Professor of Oceanography at the University of Hawaiʻi at Mānoa. "First, it provides evidence that king crabs can now disperse across the Antarctic shelf, and reproduce in at least some Antarctic shelf waters. It also suggests that these predatory king crabs will cause a major reduction on seafloor biodiversity as they invade Antarctic habitats because they appear to be eating all the echinoderms in the Palmer Deep." The researchers used a remotely operated vehicle (ROV) to explore the seafloor around Antarctic, and to evaluate the abundance and foraging behavior of king crabs in the Palmer Deep. They found that the king crab, a species known as Neolithodes yaldwyni, is acting as a major ecosystem engineer, digging in soft sediments, preying on seafloor animals and altering basic habitat structure at the ocean bottom. Echinoderms, such as sea lilies, brittle stars, asteroids and sea urchin, which generally are common and diverse in Antarctic waters, were wholly absent in the crab zone in Palmer Deep. The crab population in Palmer Deep was also both reproducing and surprisingly large; the researchers estimate that more than 1 million crabs live in the area of 146 square kilometers in water deeper than 950 m in Palmer. Smith and his co-workers also found that the Palmer Deep and Antarctic shelf waters are warming rapidly enough that the king crabs may be able to colonize the vast west Antarctic Peninsula shelf at depths of 400-600 within 1-2 decades; such colonization could have devastating ecological effects for the major components of the unique Antarctic fauna.

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