SAN DIEGO — Visiting San Diego Bay is usually peaceful for Robert Mooney, but now he sees years of work ahead to protect it.

“It is a beautiful bay but unfortunately sometimes things of beauty also suffer some tragedy,” Mooney said.  

Mooney is a marine scientist at Marine Taxonomic Services and part of the team trying to remove an invasive seaweed called Caulerpa prolifera that was discovered for the first time in the Coronado Cays area of San Diego Bay. He said Caulerpa can smother natural habitats, disrupt ecosystem and displace native plants and animals that rely on them.

“I actually want to get a little emotional. I mean, your stomach, your heart, it just sinks," he said. "You know the potential harm.”

They found about a quarter acre of Caulerpa and it’s now being covered by trained divers with a sealed barrier that will smother it. After that, it will take years of dive surveys to ensure they didn’t miss a single centimeter of the plant.

“You get in the water, you have a couple of feet of visibility, so it’s a very intensive process," Mooney said. "It would be the equivalent of putting on blinders and crawling on hands and knees to figure out how many weeds you have in your yard.”

Eileen Maher is the director of environmental conservation at the Port of San Diego. She said Caulerpa is a popular saltwater aquarium plant, although it’s illegal to own in California. She said that unfortunately, this invasion was probably caused by a careless aquarium owner.

“The most likely source is that someone cleaned out their aquarium and dumped it into either a storm drain or a gutter and it ended up in the bay, unfortunately. So if you have an aquarium, please do not do that,” Maher said.  

She said Caulerpa threatens the health of eelgrass in the bay, the cornerstone of life to various species.

“Protects fish, protects birds, protects the turtles that forage on the eelgrass habitats in the bay,” she said.

Mooney helped eradicate another species of Caulerpa that infested Agua Hedionda Lagoon in Carlsbad 20 years ago using similar methods. Even though they have years of work left to do here at the bay, it gives him hope that they can restore it.

“We’re hoping we can repeat that here and it would be very exciting to have that second win,” he said.

There is a Southern California Caulerpa Action Team made up of various agencies. They’ve also been battling an infestation in Newport Beach since 2021.

These are some of the suggestions experts are advising:

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.