How One City May Put an Alien Species to Good Work

Cameron Walker
for National Geographic News
April 12, 2005

The city of Olympia, Washington, has proposed using a pesky invasive species of water snail to help prevent storm-water flooding.

The idea: Use millions of shells from the non-native aquatic snail that infests Puget Sound. Packing them beneath city sidewalks should slow down storm-water runoff.

In December the city applied for a grant from the U.S. Environmental Protection Agency to test the plan. The results are expected soon.

The project would be a unique way of creating an economically valuable use for an invasive species, said Scott Smith, aquatic invasive species coordinator for the Washington State's Department of Fish and Wildlife. "That's what really intrigues me," he said.

Native Oysters Knocked Out

During the gold rush days, big spenders along the U.S. West Coast developed a taste for a new delicacy—the Olympia oyster. Since then the tiny Puget Sound oyster, about the size of a half-dollar coin, has remained a favorite of connoisseurs. But during the last century oyster populations began to plummet. Pollution in Puget Sound, combined with intensive oyster harvesting, made the oysters decline to near extinction.

Improved water quality in Puget Sound has allowed the oysters to recover somewhat. But now a new menace lurks below the water. An alien aquatic snail species, the arched slipper limpet (Crepidula fornicata), has made its way to the sound from its native habitat on the East Coast.

Invasive species like these snails often travel as stowaways, hitching rides in the ballast water of ships or on boat hulls. Species like this often flourish in new areas because they have no natural predators.

Slipper limpets have also made their way across the Atlantic, taking over areas off the coast of the British Isles and Northern Europe.

Researchers aren't exactly sure when this particular snail arrived in Puget Sound, which hosts dozens of other alien invaders, including some species of sea grasses and crabs. But it's certainly made itself at home, forming thick carpets of shells on the seafloor, crowding out indigenous species.

"Native species must either adapt to the new habitat created by invasive species, or die," Smith said. But management plans like this one could help mitigate the effects of the invasive, giving native oysters a fighting chance, he said.

Storm-Water Problems

Continued on Next Page >>


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