Caulerpa is a group of seaweeds that occurs naturally in tropical waters worldwide, including the Caribbean, Indo-Pacific, and Red Sea. Prized for their beauty and ability to uptake excess nutrients, many species of Caulerpa are now widely used in saltwater aquarium systems. In the 1980s, a cold-tolerant and fast-growing strain of the species Caulerpa taxifolia was cultivated in Germany and eventually distributed to aquarists worldwide.
Although many species of Caulerpa are used in aquariums, the aquarium strain of Caulerpa taxifolia is of greatest concern. It grows more rapidly, up to one half inch per day (1 cm/day), and is genetically distinct from the native strain. The aquarium strain has the ability to form a dense carpet on any surface including rock, sand and mud from just a 1-millimeter piece.
In 1984, the invasive aquarium strain was accidentally released from the Oceanographic Museum of Monaco into the Mediterranean Sea where it formed one small patch that rapidly grew into a large bed. Spread by small fragments transported primarily by boat anchors and fishing gear, Caulerpa taxifolia now blankets over 30,000 acres of seafloor off six Mediterranean countries. Fisheries and tourism have suffered as a result, and in some cases boating restrictions have been instituted to slow the spread of the species. Early eradication was not attempted in the Mediterranean, and the infestation is now considered beyond control.
In June of 2000, this same aquarium strain was discovered in California’s Agua Hedionda Lagoon in Carlsbad and again 75 miles north in Huntington Harbour. Genetic studies concluded that both California infestations were a clone of the same aquarium strain that has invaded Mediterranean AND Australian waters. The discoveries marked the first known occurrence of this strain within the Western Hemisphere and are believed to pose a major threat to coastal ecosystems, and recreational and commercial activities dependent upon coastal resources.
Improper releases of Caulerpa taxifolia from aquariums caused the California infestations. Because the infestations were detected while they were still confined, eradication efforts were promptly initiated. After six years and more than $7 million, Caulerpa taxifolia was declared eradicated from these two sites in July 2007.
Nine species banned in California
Eradication of Caulerpa from California
Facts about Caulerpa taxifolia
The problem: The aquarium strain of Caulerpa taxifolia is an extremely invasive seaweed that is currently infesting tens of thousands of acres in the Mediterranean Sea and has also been found in several locations in Australia. Genetic analysis demonstrated that the infestations discovered in southern California in 2000 were also the aquarium strain.
Aquarium use: Due to its fast-growing, hardy nature, attractive appearance, and ability to strip excess nutrients from aquariums, Caulerpa taxifolia is used as a decorative saltwater aquarium plant or in refugia. The variety of this species cultured for use in aquaria, known as the “aquarium strain,” tolerates colder water and grows more rapidly than the native strain. The native strain is not known to be invasive and is genetically distinct from the aquarium strain. It is now illegal to possess, sell or transport Caulerpa taxifolia in California.
Description: Caulerpa taxifolia is bright green, with feathery, fern-like fronds that extend upward from a main stem.
Distribution: Caulerpa taxifolia is native to tropical waters, including the Caribbean, Indo-Pacific and Red Sea. Infestations of the aquarium strain have been found in the Mediterranean Sea, Australia and California.
Growth: The aquarium strain of Caulerpa taxifolia has the ability to form a dense carpet on any surface including rock, sand and mud. It is capable of extremely rapid growth; up to one half inch per day (1 cm/day).
Depth: Caulerpa taxifolia can grow in shallow coastal lagoons as well as in deeper ocean waters, possibly to depths of greater than 150 feet (nearly 50 meters).
Ecological risks: Plant and animal diversity and abundance are reduced where Caulerpa taxifolia has invaded. The aquarium strain of Caulerpa taxifolia has been documented to displace native vegetation, particularly seagrass beds, and become the dominant plant life.
Human health threat: There are no human health risks associated with Caulerpa taxifolia.
Natural control: Outside of the tropics where Caulerpa occurs naturally, there is no known marine life that eats Caulerpa taxifolia in any significant quantities. Caulerpa taxifolia contains toxins that are distasteful to species that might feed on it.
Source and spread: Genetic evidence indicates that the most likely source of infestations in areas where Caulerpa taxifolia is not native is through releases from aquaria. Once introduced, Caulerpa taxifolia spreads by fragmentation, and even a small, broken-off fragment can form a new plant. Distances between colonies can be great due to transport on boat anchors and fishing gear. Caulerpa taxifolia does not float, has never been observed to grow on boat hulls and is unlikely to be transported in ballast water. Sexual reproduction has not been observed in the aquarium strain of Caulerpa taxifolia.
Mediterranean infestation: The aquarium strain of Caulerpa taxifolia was first found in the Mediterranean Sea off Monaco, adjacent to the Oceanographic Museum of Monaco, around 1984. Since then, Caulerpa taxifolia has spread along the Mediterranean coast and dramatically altered and displaced native plant and animal communities. Early eradication was not attempted in the Mediterranean, and the infestation is now considered beyond control. As of 2001, it was estimated that Caulerpa taxifolia had infested over 30,000 acres of seafloor in Spain, France, Italy, Croatia and Tunisia. Caulerpa taxifolia infestations have negatively impacted tourism, commercial and recreational fishing, and recreational activities such as SCUBA diving. A second species of Caulerpa, known as Grape Caulerpa, or Caulerpa racemosa, has also invaded large areas of the Mediterranean Sea, with similar biological impacts.
Australian infestation: The invasive aquarium strain of Caulerpa taxifolia has been reported in South Australia and New South Wales and is invading in a pattern similar to the Mediterranean infestation. Efforts are being made to control its spread.
Southern California infestations: Caulerpa taxifolia was first identified in June 2000 in Agua Hedionda Lagoon, a coastal marine lagoon located in Carlsbad in San Diego County. Its growth pattern was similar to that observed in the Mediterranean Sea, having spread to many areas and displaced the native seagrass. In July 2000, another infestation of Caulerpa taxifolia was reported in a portion of Huntington Harbour in Orange County. Test results indicated that the Caulerpa taxifolia in both Huntington Harbour and Agua Hedionda is genetically identical to the aquarium strain. Releases from aquaria, either directly into the water body, or indirectly through a storm drain, are the most likely sources of both southern California infestations of Caulerpa taxifolia. Caulerpa was declared eradicated from both sites on July 12, 2007, at a cost of approximately $7 million.
Legislation and regulations: Assembly Bill 1334 (Harman), signed into law by the Governor of California in September 2001, prohibits the possession, sale and transport of Caulerpa taxifolia throughout California. This bill also establishes the same restrictions on eight other species in the genus Caulerpa that are similar in appearance to Caulerpa taxifolia and that are believed to have the ability to become invasive. Earlier in 2001, the City of San Diego adopted an ordinance banning the possession, sale and transport of the entire genus of Caulerpa within city limits. Furthermore, the importation, interstate sale (including Internet sale) and transport of the Mediterranean strain (i.e., aquarium strain) of Caulerpa taxifolia is prohibited under the federal Noxious Weed Act (1999) and the federal Plant Protection Act (2000) (see State, federal and local laws).
Eradication effort: The Southern California Caulerpa Action Team, SCCAT, is a committee established to respond quickly and effectively to the discovery of Caulerpa taxifolia in southern California. The group consists of representatives from local, state and federal governmental entities, as well as private organizations. The goal of SCCAT is to completely eradicate all Caulerpa taxifolia infestations and to prevent and detect new infestations. Eradication efforts were initiated promptly after the infestations were found. Intensive surveys were conducted in waters near where the infestations were found. Wherever Caulerpa taxifolia was found, it was covered with black plastic tarps, and chlorine was placed under the tarps.
Prevention of new infestations: Aquarium water and other contents should never be emptied into or near any gutter, storm drain, creek, lagoon, bay, harbor or the ocean. Aquarium water should be disposed of only in a sink or toilet. Rock and other solid material from an aquarium should be disposed of in a trash can. Caulerpa taxifolia from an aquarium (and anything it is attached to) should be placed in a plastic bag, put in a freezer for at least 24 hours and then disposed of in a trash can. If any seaweed suspected to be Caulerpa taxifolia is found on fishing gear, anchoring gear or vessels, it should be removed, carefully bagged (since even a small fragment has the potential to regenerate into a new plant) and reported. To prevent new infestations and comply with the law, Caulerpa taxifolia should not be purchased, sold or distributed.
Contact information: Any sightings of Caulerpa taxifolia should be immediately reported to the California Department of Fish and Game at (858) 467-4218 or online through this Web site. Additional information is available from Rachel Woodfield, marine biologist and manager of efforts to eradicate and prevent infestations of Caulerpa, at (858) 560-5465.