for National Geographic News
A teeming horde of brittle stars has been discovered atop an undersea mountain chain near Antarctica, challenging long-held assumptions about the ecological role of such submerged peaks, known as seamounts.
The find, nicknamed "Brittle Star City," was made by a team surveying waters near the Macquarie Ridge, 870 miles (1,400 kilometers) south of New Zealand, as part of the Census of Marine Life, a ten-year scientific study of life in the oceans.
(Related photos: "Ocean Life Survey Reveals World of Deep-Sea Creatures" [May 2006].)
Voyage leader Ashley Rowden said the researchers were amazed as images from towed cameras revealed tens of millions of brittle stars—invertebrates related to starfish and sea urchins—feeding in the fierce currents that swirl around Antarctica.
The brittle stars occupied the very summit of the seamount, "the first occurrence, we believe, of this observation," said Rowden, a deep-sea ecologist at New Zealand's National Institute of Water and Atmospheric Research.
Normally communities of corals and sponges crown seamounts, Rowden said, but a unique combination of conditions somehow favored brittle stars in this range.
"This is a shallow seamount—it only comes up to 90 meters [295 feet]—and some species of corals and sponges ... wouldn't be able to survive at that shallow depth," Rowden said.
That left an empty niche, "which can be dominated by another filter feeder," he added.
Rowden said the area's relatively brisk 2.4-mile-an-hour (4-kilometer-an-hour) current—a result of being squeezed between adjacent seamounts—probably provides the brittle stars an abundant supply of food.
"The amount of food in the water may be just the same as anywhere else, but the fact that it's delivered at such a high rate is going to be the key factor," he pointed out.
Peter Batson, a marine biologist at New Zealand's University of Otago, said colonies of "bed forming" brittle stars have been found in other parts of the world, including U.K. and Japanese waters, though never on a seamount.
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