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Bone-Eating Worms Found in Antarctic Waters
13 August 2013 7:15 pm
When you drop a whale backbone into Antarctic waters and retrieve it a year later, you’ll find it covered with a pelt of wriggling, rosy-hued worms. Drop a chunk of wood in the same spot, and you’ll discover that it’s hardly changed. That’s the result of a simple experiment to find out if some of the world's weirdest worms also live in Antarctic waters. The discovery extends the range of bone-eating worms to the Southern Ocean and suggests that Antarctic shipwrecks may be remarkably intact.
Boneworms, known as Osedax, are among the “strangest animals of the deep sea,” says Adrian Glover, a marine biologist at the Natural History Museum in London and the lead author of the new paper. First reported in 2004, the threadlike creatures, varying from 0.6 mm to 15 mm in length, are mouthless and gutless, yet they’re able to feed on the skeletons of dead animals, including whales, birds, fish, reptiles, and even cows. Previous studies have shown that the worms form large colonies of elongated females, their trunks ending in reddish, wavy plumes that function as gills, while their greenish, rootlike structures release an acid that enables them to tunnel into the bone. The males, in contrast, aren’t readily visible, because they’re nonfeeding dwarfs that live in the gelatinous tubes surrounding the females.
Shipworms, a diverse group with the most well-known species in the family Teredinidae, are equally curious. First studied in 1733, because they were devouring the wooden pilings the Dutch used to protect their lowlands from flooding, the naked, cylindrical creatures (which are actually mollusks, not worms) bear a pair of tiny shells at one end of their bodies that they use to grind into wood. They’re the reason that Christopher Columbus abandoned four of his ships on his 1502 journey to the Caribbean. They’ve been found in nearly every ocean basin and from intertidal to hadal (6000 meters below the surface) zones.
Although not related, both boneworms and shipworms are specialists at consuming hard organic materials. Lacking mouths, both use internal symbiotic bacteria to digest their meal, and somehow both are able to locate their relatively tiny targets—a skeleton or a shipwreck—in the vast sea.
With the latter ability in mind, Glover and his colleagues designed an experiment to search for these animals in the Southern Ocean. They outfitted two old deep-sea landers, platforms designed to carry equipment or other materials to the sea floor, to carry 130 kilograms of wooden planks and whale bones, including ribs and jaws. These were deployed in December 2007 at two sites about 500 to 650 meters deep in the Bransfield Strait, on the west Antarctic Peninsula continental shelf. A third lander carried a single whale vertebra to a depth of 20 meters in Whalers Bay, near Deception Island, off the west Antarctic Peninsula. Fourteen months later, the landers were hauled to the surface.
“The bones were covered in Osedax worms,” Glover says. One whale rib alone had 202 wriggling worms per 100 square centimeters—roughly the size of a square beer mat—the team reports online today in the Proceedings of the Royal Society B. In contrast, the planks of wood were almost pristine. “There wasn’t a trace of the wood-eating worms,” Glover says.
The team wasn't really expecting to find the wood-eating worms, simply because the Antarctic continent has been treeless since about 30 million years ago. In contrast, the Southern Ocean’s abundance of baleen whales, including minke, humpback, fin, and blue whales, has likely provided a feast for bone-eating worms. Indeed, another team of researchers, including Glover, reported earlier this month their 2010 discovery of a natural whale-fall, as these skeletons are called, at a depth of 1444 meters in the Southern Ocean. It was coated in wispy Osedax worms as well.
The single whale bone the scientists dropped in the shallower waters of Whalers Bay also bore Osedax worms—extending the range of the creatures from 2893 to 21 meters below the surface. These proved to be a different species from those collected at the deeper Bransfield Strait site—so different, in fact, that the scientists say the worms must have colonized the Antarctic Ocean more than once.
Finding the bone-eating worms in the Southern Ocean and at these shallower depths “is a remarkable range extension,” says Robert Vrijenhoek, an evolutionary biologist at the Monterey Bay Aquarium Research Institute at Moss Landing, California, who was one of the co-discoverers of the Osedax genus. “It confirms that Osedax worms are present in ocean floors throughout the world,” adds Martin Tresguerres, a marine biologist at the Scripps Institution of Oceanography in San Diego, California. That it took the worms only 14 months to colonize the bones “suggests that Osedax is very abundant in Antarctic waters,” and the discovery of two markedly different species suggests they're "highly diverse," Tresguerres says.
If wood-eating worms are really absent from the Antarctic, it will be a boon to marine archaeologists, Glover predicts. Just picture famed Antarctic explorer Ernest Shackleton’s ship Endurance, which sank in 1915 in western Antarctic waters. Its pine and oak hull now lie on the sea floor, most likely pristine and intact, awaiting discovery.