Why this matters
Caulerpa outcompetes local species, and untreated it can destroy native habitats. Mitigation in California has already cost millions.
Coronado Cays, Calif. – Just below Nino the gondolier and the couple he’s paddling along for a sunset ride down canals lined by multimillion-dollar homes, a less idyllic scene is unfolding.
An aggressive algae able to clone itself from a fragment the size of a fingernail into an underwater forest that quashes nearly all other life forms has taken root.
The chance discovery of Caulerpa prolifera in the Coronado Cays in September triggered an emergency response that might seem something of the cinema. Within a day, a vast network of federal, state and local agencies were stirred into action.
“Why are the wildlife agencies treating this like such a big deal?” Jeremy Haas from the Regional Water Board asked rhetorically, acknowledging the scale of the response.
The algae smothers out native ecosystems and destroys essential food and shelter resources, pushing out a variety of marine life. It also produces a toxin that makes it inedible, which means it has no natural predators to curb its growth. Given the damage the algae has caused worldwide and the cost of mitigation, even a small outbreak is considered a significant concern. California alone has spent more than $7 million eradicating the invasive and dangerous algae.
Although it is not directly harmful to humans like recent blooms of cyanobacteria, for San Diego it would mean the destruction of native eelgrass – a focus of rehabilitation efforts for decades. Endangered green turtles are among the species that rely on the eelgrass. It also would impact the fish population, and in turn the local fishing industry.
And it almost went without notice. Had the neighborhood not ordered dock inspections ahead of some repairs the invasive bloom could have gone undetected.
No one knows for sure, but researchers say the outbreak in the Coronado Cays was most likely caused by someone dumping their aquarium water into the harbor or a storm drain. The neighborhood’s system of canals with private docks for most residents could quickly carry the algae into the marina, and potentially further.
It’s illegal to sell or be in possession of any strain of Caulerpa in California, but the algae is still known to circulate among aquarium owners.
Just one slip up by an aquarium hobbyist could have large consequences, said Robert Mooney, the marine scientist whose company, Marine Taxonomic Services, is mapping and eradicating the algae.
“I understand none of us like to have our hobbies impacted,” Mooney said. “But the stuff has shown to be such a problem around the world that I think, hopefully, folks in the industry can transition and utilize other other species.”
The clean-up has begun and the mitigation team believes they have the spread boxed in. Still, they continue to find more patches.
Jason Carroll said the Caulerpa bloom in the Cays is growing stronger than he has ever seen.
“It’s actually climbing up some of the pylons,” said Carroll, a Mooney marine technician who fought an outbreak of the algae in Newport Bay in 2021. “For algae that really doesn’t have the strongest root structure to cling, the fact that it’s like growing up stuff to me is impressive.”
“This also highlights that if Caulerpa were to get offshore,” Mooney said, “it could compete for space with species such as giant kelp and be another stressor on our coastal habitats and impact our local fisheries.”
‘It will keep growing’
Caulerpa is native to the tropics, but in the 80s a particularly resilient strain was found to grow well in cooler water and was cultivated in Europe for use in aquariums. This led to the creation of a fortified algae that could thrive in all kinds of conditions – from warm to cold, deep to shallow. Its bright green color and heartiness, plus its ability to filter and feed back nutrients into the water made it increasingly popular worldwide.
But when it was found proliferating in the sea below and well beyond the waters of Monaco’s oceanographic museum, scientists began to learn just how hearty the algae was. In less than two decades, the algae spread throughout the Mediterranean, pushing out native species across 30,000 acres of seafloor across Spain, France, Italy, Croatia and Tunisia. Today it is considered beyond control.
Haas, from the Waterboard said that is exactly why agencies in California take each incident so seriously.
“It outcompetes,” Haas said. “It becomes almost a monoculture, and it will keep growing until it runs out of areas to grow.”
Caulerpa spreads easily. It can grow over an inch per day and survive up to 10 days out of the water. It can sprout new colonies from fragments as tiny as a centimeter long. Humans amplify its opportunities to proliferate.
“You could imagine a boat going over a Caulerpa patch could create a lot of fragments and spread it,” Mooney said.
There are several different strains that have found their way to California waterways. The first was found in Agua Hedionda, Carlsbad, and cost over $6 million to tackle. Another strain, found by a diver and videographer in the 2021 Newport infestation, cost $1 million to clean up.
The bloom in the Cays was discovered when the Coronado Cays Homeowners Association called in divers to do inspections for a permit for dock improvements. Surveys are typically done as a result of applications for building permits.
The biggest concern is the impact on eelgrass in San Diego Bay and the canals in the Cays, according to Eileen Maher, director of environmental conservation at the Port of San Diego.
Eelgrass provides shelter and food for 70 species of fish and sea turtles that forage in the bay. Even birds eat the eelgrass. It has also been found to be exceptional at carbon sequestration, a process by which carbon dioxide is stored in the eelgrass bed thereby reducing emissions into the atmosphere.
“So immediate action is very important,” Maher said.
With the mediterranean Caulerpa epidemic in hindsight, California’s approach to infestations is to mitigate spread as early as possible. That led to the creation of the Southern California Caulerpa Action Team, or SCCAT– a robust multi-agency entity that includes federal, state and local agencies where the invasion has taken root.
When a surveyor discovers Caulerpa, they have 24 hours to notify the chain of authorities.
The discovery in the Coronado Cays was reported in less than half that time.
Snuffing out Caulerpa
The preferred method to kill the algae is basic, but effective – cover it with pond liner, tamp it down with sandbags and wait until it dies. After several months without sunlight, the deed is done, and unfortunately whatever else was down there with it also saw its last light.
Experts believe that the eradication process will be smooth. The water currents in the channel are relatively calm, so the liner shouldn’t be disturbed.
But when it comes to preventing future outbreaks, scientists like Mooney suggest that its critical people learn more about Caulerpa and its dangers.
“Folks that live on the water, like in the Coronado Cays and Newport Harbor,” Mooney said, “that’s where we need people to be the most vigilant.”
Type of Content
News: Based on facts, either observed and verified directly by the reporter, or reported and verified from knowledgeable sources.