Caulerpa Species on the West Coast
The genus Caulerpa comprises a group of green algae that can be highly invasive and pose a substantial threat to local marine ecosystems.
New Invasion Discovered in San Diego Bay, California
In September 2023, NOAA Fisheries was notified of an invasive algae species discovered in Coronado Cays, San Diego County, California. The algae, which is native to Florida and other subtropical and tropical locales, is scientifically known as Caulerpa prolifera. This is the second positive identification of Caulerpa prolifera on the U.S. West Coast, and is closely related to the previous eradication efforts:
- Caulerpa prolifera, previously discovered in southern California in 2021.
- Caulerpa taxifolia, previously discovered in southern California and determined to be successfully eradicated in 2006.
NOAA Fisheries believes any species of Caulerpa that is allowed to establish and spread within coastal areas of California may adversely impact local fisheries and disrupt seagrass communities important to protected species. It can grow quickly, choking out native seaweeds and potentially harming marine life through lost habitat. During the previous Caulerpa taxifolia eradication process, the Southern California Caulerpa Action Team (SCCAT) was formed. This team was made up of federal, state, and local governmental agencies, scientists, consultants, and local stakeholders.
Although there is significant concern this species could be harmful to native species, there is no danger to humans. However, it is imperative that the public avoid contact with the plant due to its extreme ease of recolonizing from tiny fragments. If you believe you have seen this invasive algae, please visit the California Department of Fish and Wildlife (CDFW’s) Reporting a Caulerpa Sighting webpage and submit a report. Please do not collect a specimen, as this may lead to further spread.
More information will be released as NOAA Fisheries continues to engage and gather more information from federal, state and local agency partners.
About Caulerpa
The genus Caulerpa comprises a group of green algae with a wide global distribution throughout the marine realm. Although primarily found in shallow tropical and subtropical waters, some species can inhabit brackish lagoons. Caulerpa species possess unique characteristics that enable them to withstand a broad range of environmental conditions and give them great invasive potential. For instance, Caulerpa species: can typically reproduce asexually through clonal fragmentation so that even tiny fragments can grow into new adults; often have a high growth rate allowing them to rapidly colonize new areas; and commonly possess a suite of toxic compounds that protect them from grazers, especially in novel environments.
The Aquatic Nuisance Species Task Force (ANSTF) is an intergovernmental body responsible for coordination of national efforts to prevent the introduction and spread of aquatic invasive species. Co-chaired by the National Oceanic and Atmospheric Administration and the U.S. Fish and Wildlife Service, the ANSTF is composed of 13 Federal and 15 ex-officio members. Recognizing the threat posed by Caulerpa species, the ANSTF developed the “National Management Plan for the Genus Caulerpa.” This National Management Plan contains specific goals to address Caulerpa at the genus level, including preventing the introduction and spread of Caulerpa and eradicating populations in U.S. waters where they are not native.
There are no Caulerpa species native to California. Therefore, Caulerpa species pose a substantial threat to marine ecosystems in California, particularly to the extensive eelgrass meadows and other benthic environments that make coastal waters such a rich and productive environment. The eelgrass beds and other coastal resources that could be impacted by an invasion of Caulerpa are part of a food web that is critical to the survival of numerous native marine species, including those of commercial and recreational importance. Infestations from two Caulerpa species, C. taxifolia and C. prolifera, have been detected in California.
Caulerpa taxifolia
Due to its fast-growing hardy nature, and attractive appearance, Caulerpa taxifolia is used as a decorative saltwater aquarium plant. The aquarium strain of Caulerpa taxifolia is an extremely invasive seaweed that has infested tens of thousands of acres in the Mediterranean Sea. In 2000, it was found in two coastal water bodies in southern California (but has since been eradicated). This "aquarium strain" tolerates colder water and grows more rapidly than the native strain. It forms dense mats and can grow up to three inches per week on any surface at depths up to 100 feet. These mats displace the native aquatic plants and animals that make our waters a rich and productive environment.
It is now illegal to possess, sell, or transport Caulerpa taxifolia in California. Signed into law in 2001, the Assembly Bill 1334 (Harman), prohibits the possession, sale, and transport of Caulerpa taxifolia throughout California. This bill also establishes the same restrictions on several other species of the genus Caulerpa that are similar in appearance and are believed to be potentially invasive.
San Diego also has adopted an ordinance banning the possession, sale, and transport of the entire genus of Caulerpa within city limits. The Federal Noxious Weed Act (1999) and the Federal Plant Protection Act (2000) prohibit the import, interstate sale (including Internet sale), and transport of the Mediterranean strain (i.e., aquarium strain) of Caulerpa taxifolia.
Caulerpa prolifera
Another Caulerpa species detected in California, C. prolifera, can grow at least as deep as 50 meters and appears more tolerant of low light environments than most other macroalgae. Like other Caulerpa species, C. prolifera can reproduce via clonal fragmentation, allowing it to rapidly colonize new areas from small fragments. C. prolifera has previously invaded soft-bottom and seagrass habitats in the Suez Canal, the Canary Islands, and Portugal, where it has negatively impacted native biota. In some areas, especially the Mediterranean Sea, seagrass meadows are being impacted, and even replaced, by Caulerpa species, including C. prolifera, which can have ecosystem scale implications. Although C. prolifera is native to certain parts of the U.S. (e.g., Florida), as noted previously, there are no Caulerpa species native to California. Therefore, like all species of Caulerpa, C. prolifera is considered a potentially highly invasive species that poses a serious threat to sensitive, native marine habitats, including seagrasses.
Any sightings of a Caulerpa species should be immediately reported to the California Department of Fish & Wildlife at 415-740-9869 (Caulerpa@wildlife.ca.gov), or NOAA Fisheries at 562-980-4037 (nmfs.wcr.caulerpa@noaa.gov)
Protect our Waters
- Learn to identify Caulerpa species
- Look for Caulerpa while fishing, boating, or diving (but avoid contacting it to avoid further spreading it)
- Do not use in your aquarium
- Before launching: Check your boat for attached plants and dispose of them in the trash
Aquarium water and other contents should never be emptied into or near any gutter, storm 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 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 is found on fishing gear, anchoring gear, or vessels, it should be removed, carefully bagged (because even the smallest fragment has the potential to regenerate into a new plant), and reported.
Report Caulerpa sightings here.
California Assembly Bill 655
In July 2023, Governor Newsom signed CA AB655 into law, enacting a statewide ban on Caulerpa. The bill was introduced with the help of Orange County Coastkeeper and California Coastkeeper Alliance.
Under AB655, Californians are prohibited from selling, possessing, importing, transporting, transferring, releasing alive in the state, or giving away without consideration all saltwater algae of the genus Caulerpa, except that in possession for bona fide scientific research.
Caulerpa taxifolia Facts
| Description | Bright green, with feathery, fern-like fronds that extend upward from a main stem |
| Distribution | Native to tropical waters, including the Caribbean, Indo-Pacific, and Red Sea; aquarium strain infestations have been found in the Mediterranean Sea, Australia, and California |
| Growth | Has the ability to form a dense carpet on any surface including rock, sand, and mud; capable of extremely rapid growth, up to one half inch per day (1.27 cm/day) |
| Depth | 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 has invaded. The aquarium strain has been documented to displace native vegetation, particularly seagrass beds, and become the dominant plant life. |
| Threats to Human Health | No associated human health risks. |
| Ecosystem Control | Outside the tropics where Caulerpa occurs naturally, there is no known marine life that eats Caulerpa taxifolia in any significant qualities. Caulerpa taxifolia contains toxins that are distasteful to species that might feed on it |
For a visual guide, please see the Guide to 9 Banned Species of Caulerpa in California.
Source and Spread
Source and Spread: Genetic evidence indicates that release from aquaria is the most likely source of Caulerpa taxifolia where it is not native. Once introduced, Caulerpa taxifolia spreads by fragmentation. 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 has infested over 30,000 acres of seafloor in Spain, France, Italy, Croatia, and Tunisia. Caulerpa taxifolia infestations negatively impacted tourism, commercial and recreational fishing, and recreational activities such as SCUBA diving.
Australia 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 infestation: The first known outbreak of Caulerpa taxifolia in the Western Hemisphere was in June 2000, when the species was found 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 was reported in a portion of Huntington Harbor in Orange County. Test results indicate that the Caulerpa taxifolia in both areas was genetically identical to the aquarium strain. Releases from aquaria, either directly into the water body, or indirectly through a storm drain, were the most likely sources of both southern California infestations.
Eradication Effort
Since the discovery of Caulerpa taxifolia at two locations in southern California in 2000, an all out effort has been undertaken to eradicate the infestations, and to locate and eradicate any other occurrences beyond the known infestation areas.
Immediate action was taken under the direction of the SCCAT. Representatives on the SCCAT included exotic species eradication specialists, researchers, resource managers, regulatory bodies, public communications representatives, the eradication contractor, and private partner stewards who were providing access, equipment, and financial resources to combat the infestation. This program included surveillance, field lab studies, eradication efforts, follow up surveys and spot treatment, support services for out-of-lagoon surveys, and assistance with public outreach.
San Diego Bay Caulerpa Eradication Plan
The SCCAT has prepared a Rapid Response Eradication Plan to address the immediate need to remove this invasive species. It is critical that the response be swift and sustained to prevent additional spread and to minimize the cost of the response effort while the infestation site is still small. Eradication efforts, which began in October 2023, include the following components:
- Control of Infestation Site - To prevent disturbance by boat anchors and boat wakes, the affected area will be controlled through coordination with local landowners. Additional visual exclusion markers will be deployed if necessary.
- Localized Eradication Level Survey - An intensive diver survey is being conducted within the affected area. Divers locate, record, and map any Caulerpa found.
- Treatment - The Caulerpa prolifera is being covered by trained divers with a sealed barrier that will kill the algae by exclusion from light, oxygen, and circulation. This method has been successfully used in the past at three other Caulerpa infestation sites.
- Post Removal Surveys - Diver surveys will be conducted both immediately following treatment and over a longer timeframe to help ensure the species is completely removed and does not repopulate the area.
- Broad Area Surveys - Diver surveys will occur in areas surrounding San Diego Bay to determine if other areas have been invaded.
Infestation in Newport Beach, CA
NOAA Fisheries worked to reactivate the SCCAT and has been collaborating with SCCAT members to quickly identify the extent of the algae’s infestation in Newport Bay. The SCCAT believed immediate action should be taken to eradicate the species, and developed the Newport Bay Rapid Response Eradication Plan (Eradication Plan). Eradication and survey efforts, consistent with the Eradication Plan, are ongoing.
Previous Caulerpa taxifolia Eradication Implementation
Containment
All identified Caulerpa patches were covered with impermeable 35mil PVC liners. The containment devices trap adequate volume of water for treatment with chemical herbicides, while protecting surrounding areas from collateral damage. This approach also prevents fragmentation of dying plants from spreading viable fragments to adjacent areas.
Chemical Control Treatment
Caulerpa patches covered with impermeable PVC lines were originally treated with injections of 5% liquid chlorine solution. Contained patches were retreated with chlorine until some residual chlorine was detected within the tarped area for a period of 24 hours. That initial methodology was modified to treat contained patches with a solid form of chlorine.
Caulerpa Control Protocol
The SCCAT developed the Caulerpa Control Protocol to detect existing infestations and avoid the spread of these invasive species to other systems. NOAA Fisheries and CDFW serve as the lead Federal and State agencies, respectively, for administering the Caulerpa Control Protocol. It outlines the certification, survey, and reporting guidelines required when surveying for all Caulerpa species in California nearshore coastal and enclosed bays, estuaries, and harbors from Morro Bay to the U.S./Mexican border. These guidelines apply to any bottom disturbing activities (e.g., pile driving, dredging, etc.) as those have the potential to fragment and spread Caulerpa. NOAA Fisheries and CDFW use the Caulerpa Control Protocol, in partnership with other resource and permitting agencies, as an important tool for conserving sensitive marine ecosystems, including eelgrass beds and other benthic habitats, and the important functions they provide.
Caulerpa Certification Exam
Caulerpa surveyor certification exams are offered virtually through NOAA Fisheries. To sign up for an upcoming exam, fill out this Caulerpa exam form.
2025 Exam Dates
Exams are tentatively scheduled for the weeks of April 15, July 15, and October 14, 2025.
Agency Information
NOAA Fisheries
501 W. Ocean Blvd., Suite 4200
Long Beach, CA 90802
nmfs.wcr.caulerpa@noaa.gov or 562-980-4037
California Department of Fish & Wildlife, Marine Region
3196 South Higuera St. Suite A
San Luis Obispo, CA 93401
Caulerpa@wildlife.ca.gov or 805-594-6172