Caulerpa Update: Invasive "Killer" Seaweed Controlled

March 5, 2004 - Updated February 2, 2005

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

Caulerpa meadow in the Mediterranean Sea. [Photo credit: University of Nice, France]

Nearly four years since the "killer seaweed" Caulerpa taxifolia was discovered in two lagoons in Southern California, biologists are cautiously claiming victory over the highly invasive seaweed. They believe the seaweed, which has smothered vast tracts of the Mediterranean Sea in a desert of green, has been controlled in the Golden State.

NOAA Fisheries, the lead federal agency in the Caulerpa eradication effort, is, however, hopeful it will be able to declare it gone, following another year of surveying.

Diver surveys have revealed no new strands of the plant in either the Agua Hedionda Lagoon in Carlsbad or Huntington Harbour in Orange County, the only two sites in North America where Caulerpa taxifolia has ever been found, since the fall of 2002.

Diagram of Caulerpa taxifolia.

Caulerpa is a hearty, tropical seaweed and a popular decorative aquarium plant. Escaped Caulerpa fragments from an aquarium in Monaco were likely the source of the now massive Caulerpa infestation in the Mediterranean Sea. The California infestation was also likely caused by someone releasing the contents of a home tank into a storm drain or nearby waterway.

Under the aegis of the Southern California Caulerpa Action Team (SCCAT), agencies including the California Regional Water Quality Control Board, the California Department of Fish and Game and NOAA Fisheries have been coordinating an aggressive eradication plan to ensure what happened in Europe would not be repeated here. Of particular concern was the potential for renegade Caulerpa fragments to escape to the open ocean. This worst-case scenario, it now seems, has been averted.

A close-up of a Caulerpa frond.

California Sea Grant has supported the vigilant Caulerpa eradication efforts led by SCCAT. In 2002, California Sea Grant was a co-host of the first "International Caulerpa taxifolia Conference," which brought together academics and resource managers to discuss eradication strategies. In 2003, California Sea Grant and MIT Sea Grant hosted the "Third International Conference on Marine Bioinvasions," at which recent research on Caulerpa was presented by leading researchers.

Size of a Caulerpa taxifolia frond in California. Possession of these once popular aquarium plants is now illegal. [Photo: Lars Anderson, USDA-ARS Exotic and Invasive Weed Research, UC Davis]

California Sea Grant has also funded two Caulerpa research projects. One, led by Susan Williams, director of the Bodega Marine Laboratory, documented aspects of the plant’s basic biology. The second, led by Steven Murray of California State University at Fullerton, was a socioeconomic study to document the prevalence of Caulerpa species in retail aquarium stores. The state legislature has since banned the intrastate sale and possession of nine Caulerpa species, including Caulerpa taxifolia.

The marine seaweed, Caulerpa taxifolia, in a California lagoon.
[Photo Rachel Woodfield, Merkel & Assoc., Inc.]