Ocean currents and polar front form 'moat' that keeps destructive mollusks at bay
Courtesy of Adrian Glover/Natural History Museum
Quirks of ocean currents may have turned the waters around Antarctica into a rare sanctuary for undiscovered wooden shipwrecks, free of the destructive mollusks known as shipworms.
The front formed by the junction of frigid polar and warmer waters as well as a strong current circling the continent may block tiny shipworm youngsters from moving in, says Thomas Dahlgren of Uni Research, the University of Bergen’s partner research company in Norway.
Fourteen months after leaving wooden planks and whale bones underwater on western Antarctica’s continental shelf, researchers found no evidence of wood-boring mollusks. Whale remains sprouted bone-eating worms but the wood emerged “pristine,” Dahlgren and his colleagues report August 14 in the Proceedings of the Royal Society B.
In most other ocean waters, including the Arctic, mollusks that specialize in boring into wood typically show up within months, Dahlgren says. Yet off-shore Antarctica is a terrible habitat for wood borers because the continent probably hasn’t grown trees for at least 30 million years. And research on other marine species has suggested that the Antarctic circumpolar current and the polar front can block some invaders from moving in.
With the results from the sunken-plank test, Dahlgren says, “it is pretty cool that our chances to find Shackleton’s ship — the Endurance, one of the most famous ships in the history of science — untouched by shipworms have increased.”
Explorer Ernest Henry Shackleton’s ship was crushed by ice and sank in 1915 during his harrowing three-year attempt to cross Antarctica.
If more exploration confirms Antarctica’s dearth of wood-boring mollusks, it would join the Black and Baltic seas as the main gaps in the world’s shipworm map — for now. “Invasive shipworms are now entering the Baltic and may well be threatening ancient shipwrecks,” says Janet Voight, a curator at the Field Museum of Natural History in Chicago.
Sea-sunken timber can attract two main groups of specialized wood-eating mollusks, the teredinids, with long wormy bodies sticking out of shells, and the more depth-loving, clamish-looking xylophagains. These deeper-dwelling wood-borers live much like the Osedax worms that bore into whale bones on the ocean floor, says marine evolutionary biologist Kenneth Halanych of Auburn University in Alabama. So he was intrigued that the experiment found that bone borers flourished where wood borers didn’t.
The submerged whale bones attracted Osedax worms, which really are worms. At least two kinds are species new to science, apparently living the specialized Osedax lifestyle of gutlessly relying on microbes to extract nutrients from fallen carcasses. Antarctica may not have trees, but it attracts plenty of whales.
Editor's Note: This story was updated on August 16, 2013, to correct Thomas Dahlgren's work affiliation.
A.G. Glover et al. Bone-eating worms from the Antarctic: the contrasting fate of whale and wood remains on the Southern Ocean seafloor. Proceedings of the Royal Society B. Posted online Aug. 14, 2013. doi: 10.1098/rspb.2013.1390 [Go to]
A.G. Glover et al. World-wide whale worms? A new species of Osedax from the shallow north Atlantic. Proceedings of the Royal Society B. Vol. 272, 2005, p.2587. doi:10.1098/rspb.2005.3275 [Go to]
D.J. Thornhill et al. Open-ocean barriers to dispersal: a test case with the Antarctic Polar Front and the ribbon worm Parborlasia corrugatus (Nemertea: Lineidae). Molecular Ecology. Vol. 17, December 2008, p. 5104. doi: 10.1111/j.1365-294X.2008.03970.x [Go to]
S. Milius. Gutless wonder. Science News. Vol. 155, July 31, 2004, p. 68. [Go to]
S. Milius. Decades of dinner. Science News. Vol. 167, May 2005, p. 298. [Go to]
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