A first: Scientists oust a marine invader.

California scientists announce they have evicted from local waters a South African worm that had been devastating area mollusks.

If confirmed, it will be "the first successful eradication of a well-established [nonnative] marine pest" anywhere, says project leader Armand M. Kuris of the University of California, Santa Barbara.

The spread of nonnative species is a large and growing problem (SN: 2/13/99, p. 103). Most go unnoticed until they are firmly established. Already widely dispersed--and lacking natural predators--they then prove all but impossible to eliminate.

The invading worm first came to light 6 years ago, when a California abalone farmer reported that his native stock was failing to grow. Shells of the sickened mollusks were no longer fairly flat, striated, and hard, but instead domed, amorphous, and crumbly. They also lacked the respiratory holes used to release materials including feces and reproductive cells.

Enter Kuris, an ecological parasitologist at the university's Marine Science Institute (MSI). Examining the shells, he discovered microscopic worms. Upon further investigation, the worms turned up in all of California's 17 other abalone farms. Carrie Culver, also of MSI, suspects that local growers unwittingly imported the pests in abalone from South Africa, where the worms had gone unnoticed.

Taxonomists Kirk Fitzhugh of the Los Angeles County Museum of Natural History and Greg Rouse of the University of Sydney in Australia now report that this abalone worm represents a new genus and species. In the fall INVERTEBRATE BIOLOGY, they christen it Terebrasabella heterouncinata.

"In the worst case, there can be thousands of these worms per shell," observes Culver. She's found that they induce abalone to secrete a protective tubelike shell over them. Once covered, the worms thrive even if their host dies.

Economic losses due to the worm have already put one pioneering California abalone grower out of business, notes Culver. The epidemic, however, didn't stay confined to shellfish farms. In 1996, she and Kuris discovered the worm in coastal waters just outside an abalone farm north of Morro Bay.

The scientists immediately coaxed local public and private agencies into recruiting volunteers to cull the affected waters of aquaculture debris and some 1.5 million large snails, which the pests also infect. Their goal: to reduce local mollusks so that larval worms fail to find a host and simply die off.

"It's now been 2 years since we've seen any sign of infestation," Kuris says.

Unable to swim, the microscopic worms must crawl in search of a host. Kuris' team owes its success to identifying and quickly "exploiting this slow dispersal--the pest's Achilles' heel," says Elliott A. Norse of the Marine Conservation Biology Institute in Redmond, Wash.

"It's a marvelous example of the way we should deal with eradications," agrees Roger Mann of the College of William and Mary's Virginia Institute of Marine Science in Gloucester Point, Va. He only wishes he could find a similar vulnerability in the life cycle of another new invader--a voracious oriental whelk threatening shellfish in the Chesapeake Bay.