The dreaded wood-eating shipworm is invading northern Europe's Baltic Sea. The animal threatens to munch through thousands of Viking vessels and other historic shipwrecks, scientists warn.

The sea's cool, brackish waters have for centuries protected the wrecks from the wormlike mollusks. But now global warming is making the Baltic Sea (map) more comfortable for the critters, a new study speculates.

Shipworms, which can obliterate a wreck in ten years, have already attacked about a hundred sunken vessels dating back to the 13th century in Baltic waters off Germany, Denmark, and Sweden, reported study co-author Christin Appelqvist.

"Since 1990 there has been a big range expansion in the southern Baltic," said Appelqvist, a marine biologist at the University of Gothenburg in Sweden.

Until recently the wood-boring molluscs, which generally require relatively salty waters, were unable to survive in the low-salt Baltic.

Why shipworms are suddenly able to spread there remains a mystery, but studies suggest rising sea temperatures have something to do with it. In warmer water the animals, Appelqvist said, appear to be somehow "less stressed" by low salinity.

Global Worming Disaster?

The shipworm invasion could prove disastrous for marine archaeology in the region, home to long-submerged prehistoric timber settlements and remarkably preserved wrecks such as the salvaged 17th century Swedish warship the Vasa, a major museum attraction in Stockholm.

To defend the region's well-preserved wrecks from shipworms, researchers have suggested draping submerged vessels in polypropylene covers or covering ships with seabed sediments and sandbags.

Such a project could reach positively oceanic proportions, given that the Baltic holds about a hundred thousand well-preserved shipwrecks—and counting.

"Really nice tall ships with the mast and everything intact are still being discovered," Appelqvist said. "Every time [researchers] go down there with remotely operated vehicles they find new wrecks."