Scientists monitoring eelgrass transplanted to the lagoon as part of a restoration effort found a patch of C. taxifolia measuring about 30 by 60 feet, and nine smaller patches. Eradication efforts began immediately. A coalition of 10 federal, state, and county agencies and two private companies are attacking the alga with chlorine, which kills the plant in laboratory conditions. The first treatment seemed to be successful on the small patches.

This clone of C. taxifolia, a tropical Pacific species, was developed in the 1970s at the aquarium of the zoo at Stuttgart, Germany, as an attractive, fast-growing warm-water aquarium plant. It was distributed freely to other European aquaria, including the Monaco Aquarium. It has now covered over 10,000 acres of the Mediterranean seafloor, wiping out native seagrasses and other plants, invertebrates, and many fishes, creating monotypic meadows that rapidly eliminate habitat and diversity.

The clone grows much faster and many times larger than the original species. It tolerates cold water, adapts to any kind of seafloor habitat, and contains a toxin that, though not harmful to humans, kills many marine organisms. It propagates by fragmentation—new plants can start from one-millimeter bits of frond, and a single plant can have as many as 200 nine-foot-long fronds—so it is easily spread by boat anchors and fishnets. Many methods of eradication had been tried, with little success; often the plant returns even more vigorous and tenacious than before. Mediterranean regions have already felt significant economic impacts on tourism, recreational diving, and commercial fisheries. Though little known in the U.S., there is extensive documentation of European studies, conferences, and eradication efforts.

Recognizing the perils the C. taxifolia clone would pose if introduced to American waters, in 1998 100 scientists petitioned the federal government to ban importation, sale, and possession of the plant. In 1999 the federal government imposed the ban, designating C.taxifolia a prohibited species under the Federal Noxious Weed Act. It is still sold and distributed by the aquarium business in some countries, however. (A web search found aquarium enthusiasts eagerly requesting stalks of Caulerpa from others whose tanks were overgrown. It was not possible, however, to determine whether the invasive clone was among those discussed.) There is hope that the California invasion may have been caught early enough to eradicate this “killer alga” before it spreads, but scientists also fear that its eventual introduction and spread may be inevitable and unstoppable. Game wardens are posted around the clock at Agua Hedionda Lagoon to prevent anyone from carrying away pieces of the killer alga.

—HMH

For more information see Caulerpa taxifolia links at: www.sfei.org/invasions.html (San Francisco Estuary Institute).