Killer Algae May Have Reached California

A volleyball-court-sized patch of bright green algae in a San Diego lagoon has set off alarm bells among ecologists and officials. Scientists strongly suspect that the algae, Caulerpa taxifolia, is the same fast-growing, non-native clone that has swept over the northwestern Mediterranean sea floor in the past decade with devastating ecological consequences. A consortium of agencies and private groups has cordoned off the lagoon and is laying plans to poison the seaweed.

Scientists say such actions are needed to preserve biodiversity in the face of voracious non-native plants and animals (Science, 17 September 1999, p. 1834). "It's a rare chance to stop an invasion once it's started," says marine biologist Andrew Cohen of the San Francisco Estuary Institute.

C. taxifolia is native to various tropical seas. In 1980 an aquarium in Stuttgart, Germany, began sharing with other aquaria a showy clone that grew fast in cold water. The organism's potential for triggering an ecological disaster didn't become apparent, however, until 1989, when French scientist Alexandre Meinesz noticed a flourishing C. taxifolia patch in the waters off the Monaco aquarium. The alga now carpets 4600-and-counting hectares of sea floor, wiping out native grasses from Spain to Croatia.

The story was familiar to Rachel Woodfield, a marine biologist with the consultant firm of Merkel & Associates in San Diego, who spotted some unfamiliar seaweed growing in a lagoon in mid-June. The 10-meter-by-20-meter patch and smaller, scattered patches had apparently edged out the eelgrass within a few years. Woodfield consulted with algae experts, including Meinesz, who fingered the Mediterranean clone or one just as invasive.

And that set off alarm bells. If the alga, now 30 kilometers north of San Diego, gets loose throughout California, says Bob Hoffman of the National Marine Fisheries Service Southwest Region, "the whole rocky reef plant and animal assemblage off our coast would be dramatically transformed."

Experts are now awaiting results of genetic tests to confirm the invader's identity. But with evidence pointing toward the Mediterranean clone, 10 agencies and groups are already scrambling to wipe out the algae. As a first step, they've quarantined the lagoon, owned by a power plant and used as for boating, to prevent tiny fragments of C. taxifolia from being spread by boat anchors. Within a week or two, they plan to cover the seaweed patches with tarps soaked with an herbicide, most likely chlorine or copper sulfate. The next step is long-term monitoring, including pamphlets to alert boaters and divers to look out for other colonies. "This is almost a test case of the new resolve to deal with this problem" of invasive species, says ecologist Daniel Simberloff of the University of Tennessee, Knoxville.

Related sites
Review of Killer Algae in Science
Caulerpa taxifolia's Mediterranean invasion
U.S. Aquatic Nuisance Species Task Force