Invasive seaweed found in San Diego Bay prompts warning from agencies

SAN DIEGO — The discovery of invasive seaweed in San Diego Bay has prompted authorities to issue a warning to the public to not drain saltwater aquariums into area waterways.

The Port of San Diego, the Southern California Caulerpa Action Team (SCCAT), the City of Coronado, and the Coronado Cays Homeowners Association (CCHOA) are responding after invasive seaweed — Caulerpa prolifera — was found in the Coronado Cays area of San Diego Bay in late September.

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Divers found a patch of the invasive seaweed during an “in-water pre-construction eelgrass/Caulerpa dive survey as a permit condition for a dock replacement project,” The Port of San Diego reported. More invasive seaweed was found in follow-up surveys.

The invasive seaweed found is an algae native to Florida and subtropical and tropical areas. The warning from The Port of San Diego states the invasive plant can overtake native plants, which would also impact the animals that rely on those plants to live.

It is illegal in the state of California to “possess, sell, or transport any Caulerpa seaweed.” Those in violation can be fined $500 to $10,000.

In San Diego Bay, state and federally protected eelgrass habitats are at risk as native green sea turtle populations, a threatened species, feed on it; 70 different fish species also rely on eelgrass.

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According to the National Oceanic And Atmospheric Administration (NOAA) eelgrass is essential in Bay areas, providing shelter, food, foraging areas and spawning surfaces for different species. Eelgrass also improves the water quality by filtering polluted runoff, storing carbon dioxide and absorbing excess nutrients. It also protects the shoreline from erosion.

The federal government designated eelgrass as Essential Fish Habitat (EFH) and a Habitat of Particular Concern under the Magnuson-Stevens Fishery Conservation and Management Act in 1996.

Caulerpa alternatively does not pose a risk to beachgoers. However, it can spread when it comes in contact with boats, fishermen, and from tidal exchanges.

Boaters, kayakers, swimmers, and divers are asked to avoid the affected areas at this time. A warning to not dump saltwater aquariums into San Diego waterways has also been issued as Caulerpa is a common saltwater aquarium plant.

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If you have or sell saltwater aquariums:

  • DO NOT use Caulerpa in your aquarium.

  • DO NOT dump your aquariums into California waters or even pour the contents into streets or down storm drains that often discharge to the bay or ocean. ONLY drain aquariums into sinks or toilets as the water will circulate to a treatment plant that would help minimize the threat.

  • DO NOT share or sell Caulerpa.

If you are a boater, diver, or fisherman:

  • Learn what Caulerpa looks like and keep an eye out for it.

  • Inspect your anchor, fishing gear, or nets for Caulerpa that may have been picked up from the bottom.

  • Learn more and report sightings to the California Department of Fish and Wildlife at

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The state of California has been routinely monitoring Caulerpa since the early 2000s.

The Port of San Diego noted this is the first discovery of the invasive seaweed in San Diego Bay.

An infestation in Newport Bay has been ongoing since 2021. Another species of Caulerpa infested part of Huntington Harbour and Aqua Hedionda Lagoon in Carlsbad in the early 2000s.

In response to the discovery of the invasive seaweed in the San Diego Bay, several action items have been established. The SCCAT Rapid Response Eradication Plan includes the following:

  • “Control of Infestation Site – To prevent disturbance by boat anchors and boat wakes, the affected areas are being controlled through coordination with the CCHOA and slip occupants.”

  • “Localized Eradication Level Survey – Diver surveys are being conducted within and adjacent to the affected area. Divers locate, record, and map any Caulerpa prolifera 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 other Caulerpa infestation sites in other areas of Southern California.”

  • “Post Treatment Surveys – Diver surveys will be conducted both immediately following treatment and over a longer timeframe to help ensure the species is completely eradicated and does not repopulate the area.”

  • “Broad Area Surveys – Diver surveys will occur in surrounding areas of San Diego Bay to determine if other areas have been invaded.”

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The Port of San Diego has contributed $92,000 towards surveys and eradication to date. The Port and the U.S. Fish and Wildlife Service have applied for a grant from the Rapid Response Fund for Aquatic Invasive Species to cover any additional costs. Additional funding may also be available from the State Water Resources Control Board’s Cleanup and Abatement Account.

The SCCAT includes representatives from the California Department of Fish and Wildlife, Santa Ana Regional Water Quality Control Board, the California Coastal Commission, California State Lands Commission, NOAA Fisheries, Army Corps of Engineers, U.S. Fish and Wildlife Service, and partnerships with the San Diego Regional Water Quality Control Board and State Water Board.

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