Caulerpa prolifera
The invasive Caulerpa prolifera seaweed found in San Diego Bay. Photo released by Port of San Diego

An invasive seaweed found in the Coronado Cays area of San Diego Bay prompted the Port of San Diego and city of Coronado to Thursday release a plan to deal with the species.

Caulerpa prolifera, an algae native to Florida and other subtropical and tropical locales, can take over non-native natural habitats, disrupting the ecosystem and displacing native plants and the animals that rely on them, a port statement said.

The Southern California Caulerpa Action Team (SCCAT) and Coronado Cays Homeowners Association joined the port and city in the response.

In late September, divers found a small patch of the plant while conducting an in-water, pre-construction eelgrass/Caulerpa dive survey as a permit condition for a dock replacement project. Additional patches were discovered nearby during follow-up surveys. The total find within the Cays is about one-quarter of an acre.

According to a port statement, in San Diego Bay, state and federally protected eelgrass habitats are especially at risk as eelgrass is utilized by native green sea turtle populations, a threatened species, and 70 different fish species rest within and feed on eelgrass. Caulerpa is not harmful to humans.

It is illegal in California to possess, sell, or transport any Caulerpa seaweed. Caulerpa is used primarily in saltwater aquariums. Fines can range from $500 to $10,000 for each violation.

“Caulerpa can rapidly and aggressively expand from contact with vessels, fishing, and even tidal exchanges,” the port statement reads. “To prevent unintentional spread of this invasive species, boaters, kayakers, swimmers, and divers are asked to avoid the areas, if possible, or to gently transit the channel at high tide.”

In response, the SCCAT prepared a Rapid Response Eradication Plan that includes controlling the site, continuing local diving surveys to search for more, treating and killing the algae and post-treatment surveys.

The Port of San Diego has contributed $92,000 to the plan to date, but the final cost is yet to be determined, the port statement said. To assist in covering remaining costs, the port and the U.S. Fish and Wildlife Service applied for a grant from the Rapid Response Fund for Aquatic Invasive Species. Additional funding may also be available from the State Water Resources Control Board’s Cleanup and Abatement account.

According to the port, the most likely source of this infestation is the release from a saltwater aquarium into the bay, as Caulerpa, though illegal, is a popular and common saltwater aquarium plant. Those with saltwater aquariums are urged to not use the plant and to not dump the contents into California waters or on the street. Only use a drain in your residence, as those lead to treatment facilities that can help minimize the threat.

Boaters, divers and fishermen are urged to learn what it looks like, keep an eye out and inspect gear for any algae that may have been picked up from the bottom.

“This is the first discovery of Caulerpa prolifera in San Diego Bay and an infestation in Newport Bay has been battled since 2021,” the port statement read. “Another species of Caulerpa infested part of Huntington Harbour and Aqua Hedionda Lagoon in Carlsbad in the early 2000s. In California, there has been routine monitoring of Caulerpa since the early 2000s.”

–City News Service