Rogue alga routed

One of the world’s worst weeds, Caulerpa taxifolia, has been eradicated from a lagoon in southern California, government officials reported last month. It was the alga’s only known invasion in the Western Hemisphere.

Once marketed globally for use in aquariums, this captive-reared alga seems to have evolved into a form quite unlike its wild brethren (SN: 7/4/98, p. 8: http://www.sciencenews.org/pages/sn_arc98/7_4_98/bob1.htm). For instance, the escaped alga survives winter chills that would kill its wild kin and has almost no predators. Like a dense shag carpet, it smothers natural underwater inhabitants. Since the species’ release in Monaco 2 decades ago, the alga has blanketed large portions of the Mediterranean. The U.S. infestation seemed to have resulted from a separate aquarium discard.

Immediately after the alga’s discovery in the Agua Hedionda Lagoon in Carlsbad, Calif. (SN: 7/15/00, p. 36: Ultimate Sea Weed Loose in America), government and private organizations created an action team. Whenever team members found Caulerpa, they put a tarp over it and poisoned it with chlorine. In March, the team reported that its regular surveys of the lagoon during the past 4 years had found no sign of the alga. The invader had initially covered roughly 1,500 square meters of the lagoon.

Had the alga not been contained, “it would have irreversibly changed the ecosystem in California’s near-shore coastal environment,” says Tim Keeney, deputy assistant secretary of the National Oceanic and Atmospheric Administration. “It was only through the rapid response and cooperative efforts of organizations at all levels that we were successful in preventing an ecological crisis.”

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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