By SDCN Staff
San Diego, CA–The Port of San Diego has renewed its local emergency declaration to continue the fight against an invasive alga known as Caulerpa (Caulerpa prolifera) in San Diego Bay.
The port secured $200,000 in new grant funding from the Pacific States Marine Fisheries Commission to support additional diver surveys and eradication efforts.
The Board of Port Commissioners first adopted the emergency declaration on November 14, 2023, after Caulerpa was discovered in the Coronado Cays. Since then, the Board has approved 18 continuances of the local emergency, most recently extending it an additional 60 days through March 15.
Caulerpa is a fast-growing, highly invasive tropical alga that spreads through fragmentation driven primarily by tidal movement, vessel traffic, and fishing activity, further contributing to its dispersal. While it is not harmful to humans, the alga can quickly choke out native seaweeds and eelgrass, threatening marine habitats throughout the bay.
Protecting eelgrass habitat is a top priority for the Port. San Diego Bay is home to nearly 2,600 acres of eelgrass, including about 1,900 acres in the South Bay. Eelgrass is the base of the food chain and provides food and shelter for dozens of species, including more than 70 types of fish and over 100 endangered green sea turtles. It also supports a healthier environment by helping improve water quality and capturing and storing carbon.
Caulerpa was first discovered in September 2023 during a routine dive survey tied to a dock replacement project in the Coronado Cays. Follow-up surveys revealed additional patches in and around the Cays. In April and August 2025, divers also found small patches in the nearby San Diego Bay National Wildlife Refuge. To date, approximately 11,300 square feet of Caulerpa have been identified in San Diego Bay, of which more than 300 square feet is within the Port’s jurisdiction.
Trained divers have covered all known patches with sealed benthic barriers, which kill the alga by cutting off light, oxygen, and water circulation. This method has been successfully used in other Southern California eradication efforts.
The port is working closely with the Southern California Caulerpa Action Team, a coalition of state and federal agencies coordinating a rapid response to prevent further spread. As part of the eradication process, two years of monitoring with no discoveries are required before the alga can be declared fully eradicated.
Divers, including Port Field Operations staff, continue surveying South San Diego Bay, which spans roughly 3,000 acres. Funding from federal, state, and Port sources has supported these efforts, and additional resources continue to be pursued.
To date, more than $3.1 million has been committed to surveys and eradication, including $1,192,000 from Port funds, $600,000 from State of California funds, and over $1 million awarded to the San Diego Bay National Wildlife Refuge Complex from the Bipartisan Infrastructure Law, Inflation Reduction Act, and other federal sources. Most recently, the Port was awarded $200,000 from the Pacific States Marine Fisheries Commission’s Aquatic Invasive Species Rapid Response Fund. The program, in cooperation with the U.S. Fish and Wildlife Service, provides grant funds to rapidly deploy measures for newly discovered invasive species found in freshwater and marine environments. Continuing the local emergency declaration helps the Port remain eligible for these critical funds.
The September 2023 finding is the first discovery of Caulerpa in San Diego Bay. Similar infestations have been discovered and are actively being addressed in Newport Bay, and other Caulerpa species were successfully eradicated from Huntington Harbor and Agua Hedionda Lagoon in the early 2000s following the same benthic barrier treatments that are now being applied in San Diego Bay.
The most likely source of the infestation is the release of aquarium contents into the bay. Because of the environmental risk, it is illegal in California to possess, sell or transport any Caulerpa species. Violations can result in fines ranging from $500 to $10,000 per incident.
The Port of San Diego offers advice for individuals who have or sell saltwater aquariums:
- Do not dump any aquarium species into California waters or pour the contents down storm drains or into sewer systems.
- Bleach aquarium water (1/3 cup of bleach per gallon of water for 10 minutes) before dumping the bleached aquarium water into a household drain that will lead to a treated sewer system.
- Do not purchase, share, or sell Caulerpa.
- Do not use Caulerpa in your aquarium.
- Freeze any suspected Caulerpa and attach substrates for at least 48 hours before disposing of it in the garbage.
Boaters, kayakers, swimmers, and divers are also asked to avoid infested areas when possible and to gently pass through at high tide if avoidance is not feasible. Anyone who spots suspected Caulerpa is encouraged to report it to the California Department of Fish and Wildlife website.
