May 12, 2002

Contact: Christina S. Johnson,, 858-822-5334


A.Meinesz, University of Nice, showing Caulerpa in an aquarium.

In June of 2000, a group of divers went for what they thought would be a routine swim through a gently undulating eelgrass bed in the Agua Hedionda Lagoon in northern San Diego County. Working on a restoration project, paid for by the owners of the nearby power plant, they swam transects across the eelgrass bed, measured its length and width and noted new shoots. Everything was normal, humdrum even, until one of the divers came face-to-face with a large patch of unusually green, beautiful feathery seaweed. The strange seaweed would later be identified as the first confirmed North American sighting of "the killer algae" blighting Mediterranean waters of southern Europe.

Subsequent genetic tests showed that the seaweed specimens were clones of the Mediterranean


A.Meinesz, University of Nice

If you see or suspect this seaweed, DO NOT DISTURB IT, report it immediately to the Caulerpa Action Team at : (858) 467-2952

strain. The seaweed, technically a green alga, is known scientifically as Caulerpa taxifolia. The French media dubbed it "the killer algae" over fears the renegade aquarium plant was poisoning seafood. Although the alga does contain predator-repelling toxins, it is not considered a threat to human health. In the Philippines, where the taxifolia strain grows naturally, people eat the seaweed and enjoy the slight stinging sensation caused by its chemical defense system.

The nickname "killer," however, is appropriate to a certain extent. Although the seaweed does not "do combat" with other photosynthesizing organisms, its ability to grow rapidly, to grow over boulders, seawalls, in mud, sand or on rocks has the effect of severely reducing populations of native seaweeds and seagrasses. Because fish, invertebrates and seabirds need native habitats to survive, Caulerpa outbreaks can dull the biological richness of marine ecosystems. The ecological problems associated with Caulerpa are exacerbated by the fact that Caulerpa can spread ten times fast than other seagrasses.


Photo: A. Meinesz, University of Nice

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In America, as in Europe, wildlife agencies are focused on trying to prevent the seaweed from spreading into the open ocean where containment efforts would be doubly futile.

Why is the alga such a problem?

Fishermen detest the seaweed because it clogs nets and makes them heavy to haul up. Divers and tourists prefer an aesthetically pleasing underwater landscape, teaming with fish, shells and bouquets of plant life. Caulerpa meadows have been compared to wet, overgrown Astroturf. In California, the seaweed threatens protected habitats, such as the eelgrass --- essential habitat for lobsters, flatfish and bass. Many animals would suffer if the state lost its native kelps and marine grasses.

In California, there is cautious optimism that Caulerpa can be controlled because the initial infestations


Photo: A. Meinesz, University of Nice

Like curing cancer, early detection is also crucia


are limited and because of the prompt reaction by government agencies to handle the situation. As of March, there were only two known infected areas in the country: the lagoon in San Diego County and Huntington Harbor, which was reported in July, soon after the first discovery.

"We are acting very rapidly to eradicate it," said Lesley Dobalian, an environmental specialist at the California Regional Water Quality Control Board in San Diego. "We have an extensive outreach program, and we are pursuing legislation."

Both infestations are being treated, with funds from a multi-agency organization, known as SCCAT, or the Southern California Caulerpa Action Team. The California Regional Water Quality Control Board, which is charged with upholding state and federal clean water laws, is leading the eradication program, in conjunction with agencies such as the Department of Fish & Game, California Department of Food & Agriculture, the National Marine Fisheries Service, the U.S. Fish & Wildlife Service and the California Sea Grant Program.


Photo: Alexandre Meinesz, University of Nice<

. . .Woodfield said that Caulerpa could be the biggest single-celled organism on the planet. It can reach lengths of 9 feet.

Merkel & Associates, the same biological consulting firm that discovered the Caulerpa, has been hired to perform the eradication. "We put tarps over the Caulerpa patches," said Rachel Woodfield, the biologist in charge of the project. "The tarps are sealed to the bottom, and the patches are then chlorinated."

The tarps, thick sheets of black plastic, starve the plants of sunlight. "If the Caulerpa is under the tarp, it is toast," she said. Once the tarps are in place, she monitors for re-growth outside the tarps. New sprigs, of which there have been many, are then treated.

As of March 2001, about one-fifth of the Agua Hedionda Lagoon bottom was covered with tarps, she said.

In Huntington Harbor the same strategy has been employed: tarps, chlorine and monitoring. Huntington Harbor, however, has been slightly more difficult to purge. Not only the Harbor but also two adjacent ponds are brimming with Caulerpa. The ponds have not been covered and chlorinated because, for the last two months, heavy rains closed waters to diving. Now that bacterial levels have returned to normal, Woodfield can begin laying down tarps. In the meantime, the ponds have been outfitted with filtering devices that remove small pieces of seaweed from out-flowing waters.

Even small pieces of the seaweed can grow into whole new colonies, Woodfield said. This biological quirk and others makes eradicating Caulerpa very challenging.

Amazingly, Caulerpa is single-celled with multiple nuclei. Because of its unusual single-celled structure, any fragment of the plant that contains a nuclei and a chloroplast --- the structure that allows


Photo: Alexandre Meinesz, University of Nice

for photosynthesis --- is capable of growing into a new plant. Tiny fragments of the plant cut apart by boat propellers, for instance, can spread Caulerpa.

All one has to do is look at how the seaweed spread in the Mediterranean to know how quickly the plant can spread asexually. In the mid-80s, only one square meter of Caulerpa claimed the seafloor as its home. By 1989, it had usurped more than 2 acres. Despite costly eradication schemes, by 1997 more than 11,000 acres were smothered in a dense blanket of swaying feathery green fronds. To slow the spread, harbors were forced to close their docks to boats; fishing grounds were also closed to commercial and sport fisherman for the same reason.

In the last five years, the alga has spread to North Africa, Australia and California. Genetic tests have shown that Caulerpa specimens in America and the Mediterranean are clones of specimens cultured and displayed at the Stuggart Museum in Germany in the early-80s.

Can it be eradicated?

One Sea Grant scientist was not too optimistic about eradicating Caulerpa any time soon.

"I am concerned because Caulerpa has underground tissue, rhizoids, the algal equivalent of roots, that go 15 cm into the sediments," said Susan Williams, Director of Bodega Bay Marine Lab at UC Davis, a member of the SCCAT team and a California Sea Grant researcher. She believes the chlorine might not be reaching their roots.


Photo: A.Meinesz, University of Nice

"I am further concerned because in Agua Hedionda, Caulerpa is now growing next to the treatment tents. Although it is assumed that this new growth is remaining fragments made during the eradication treatments in the summer, I wonder if the rhizoids had not grown out from under the tents. In my experience with this seaweed, this is entirely within its capacity and even likely to happen."

Williams has been funded by California Sea Grant to identify areas that may be especially vulnerable to invasive seaweed infestations. People are assuming the high-risk areas are quiet bays, she said. "We also are fairly confident that Caulerpa will also show up most likely in bays close to humans."

Williams said that environmental factors, such as water pollution and nutrient levels, might influence Caulerpa's ability to invade.

"Based on scientific studies in the Mediterranean and on my research, sea grass beds that are degraded are less resistant to Caulerpa invasion," she said.

Consistent with this, the Department of Fish & Game has identified Newport Bay, Dana Point, Marina Del Rey, Mission Bay and San Diego Harbor as areas at high-risk of invasion. These are all urbanized waterways where it is believed there are a relatively high percentage of homeowners with saltwater tanks.

In upcoming months, the Department of Fish & Game will begin surveying these high-risk areas, visually and with side-scan sonar. Large stands of the seaweed grow in circular patterns that can be discerned easily in acoustic images.

Another issue is the sale of Caulerpa at local aquarium shops.

Under the Federal Noxious Weed Act of 1999, it is a federal offense to import Caulerpa taxifolia or


Photo: A.Meinesz, University of Nice

transport it across state lines. But it is still legal to buy and sell Caulerpa within the state of California. Pending state legislation (Assembly Bill 1334) would prohibit the sale, possession, transportation, or giving away without consideration the saltwater algae of the genus Caulerpa."

Biology professor Steve Murray at Cal State Fullerton and Susan Frisch, a California Sea Grant Trainee working with Dr. Murray, are currently receiving Sea Grant funds to conduct a survey of aquarium retailers in Southern California. Their goal is to determine the number of species of Caulerpa being sold in the area and the percentage of stores that sell Caulerpa species.

Public outreach and education, however, may be the key to stopping Caulerpa. "The biggest issue is education," Bill Paznokas, a biologist with the Department of Fish and Game, said. "People need to know they cannot release the contents of their home aquariums into lagoons and harbors."

Like curing cancer, early detection is also crucial. Fish & Game staff and others on the SCCAT team will soon begin training recreational divers to learn how to identify new patches of Caulerpa. "They will become another pair of eyes in the surveillance project," Paznokas said.

In addition, public aquariums such as the Birch Aquarium at the Scripps Institution of Oceanography are involved with public outreach to teach students and visitors about the algae, what it looks like, and why it is important not to discard home tanks into waterways. The SCCAT team is asking people who think they may have found a new outbreak, not to disturb it. It asks residents to "note as much information as possible about the location where it was found" and to report it immediately to the Southern California Caulerpa Action Team at (858) 467-2952.

FACT SHEET: Caulerpa taxifolia

ISSUE: The popular home aquarium plant has been introduced into the wild and has proven to be highly invasive in the Mediterranean Sea. The first outbreak in North America was discovered in June 2000 in a shallow lagoon in northern San Diego County.

WHAT DOES IT LOOK LIKE? It is an attractive seaweed with bright green stems and feathery fronds.

WHY IS IT PROBLEM? It expatriates native seaweeds and grasses that support fish, seabirds and invertebrates in California. The main ecosystem under threat is eelgrass beds, which are essential habitat for California spiny lobsters and halibut.

WHERE IS IT FOUND NATURALLY? It is a tropical plant, native to the warm waters of the Caribbean, Indonesia and Southeast Asia. Although not a pest in its native ranges, it grows like an angry weed where it is exotic.

WHAT IS ITS NON-NATIVE RANGE? It has spread extensively in the northwestern Mediterranean (more than 11,000 acres of the seafloor are blanketed by the seaweed.) It is also found in the southern Mediterranean off North Africa, Australia and now California.

WHERE IS IT IN CALIFORNIA? In the Agua Hedionda Lagoon in northern San Diego County and in the Huntington Harbor in Orange County.

HOW DID IT GET HERE? Most likely, people who dumped home saltwater aquariums into nearby waterways have caused the infestations.

HOW DOES IT SPREAD SO FAST? It can grow as much as 3 inches a day, and reproduces asexually so that tiny pieces of the seaweed can grow into whole new plants.

WHAT IS BEING DONE? Tarps are put over infested areas and chlorine is applied. Target lagoons and bays will be surveyed in an effort to catch outbreaks early. There is pending state legislation that would ban the sale and possession of all species of Caulerpa, including the taxifolia.

Sea Grant Takes Action on Caulerpa Outbreak

When news of the nation's first "killer algae" outbreak was announced, California Sea Grant immediately began participating in an aggressive statewide effort to prevent the seaweed from spreading the way it has in the Mediterranean, with devastating consequences for marine life.

Under its Rapid Response program, California Sea Grant has funded three projects to reinforce and expand the state's already aggressive eradication program, known as SCCAT, for Southern California Caulerpa Action Team. Caulerpa taxifolia, the scientific name for the "killer algae," is a popular, decorative aquarium plant. The outbreak, discovered in a San Diego lagoon in June 2000, was likely caused by someone dumping a home saltwater aquarium into a waterway.

To help quantify the prevalence of Caulerpa in retail stores, California Sea Grant has funded Steven Murray, a biology professor at Cal State Fullerton, and Susan Frisch, a Sea Grant Trainee, to conduct a survey of aquarium shops in Southern California. The researchers are tracking the number of species of Caulerpa being sold, and the percentage of stores selling Caulerpa taxifolia, among other things. Murray is also buying seaweed specimens and then identifying them, because often more than one species is sold under the same common name. By classifying specimens, the researchers will be able to identify the species' native ranges and identify which plants might be able to survive in California waters if let loose. He said that many species besides Caulerpa might have the potential to menace marine environments.

Because little is understood about the basic ecology of Caulerpa in California, Susan Williams, Director of the Bodega Bay Marine Lab, University of California at Davis, has been funded to examine some basic scientific questions about the seaweed. Her Sea Grant project is focused on mapping the geographical limits of the seaweed's range in California. In particular, Williams will determine the relationships between the seaweed's growth rates and physical quantities such as light, water temperature and salinity. This information will help identify those areas most vulnerable to infestations. Monitoring programs can then focus on these target areas, places such as Mission Bay and Newport Harbor.

At present, public outreach is considered the most crucial component of a successful eradication plan since it is home aquarists that are likely spreading the seaweed. To help educate the public about the dangers of letting pets loose in lagoons and bays, Sea Grant funded Enric Sala, a researcher at Scripps Institution of Oceanography, to put together a Caulerpa poster for exhibition at the Scripps Institution of Oceanography's Birch Aquarium. The exhibit shows pictures and explains basic facts about the seaweed: what it looks like, why it is a problem in the wild, and what to do if some is found.

Under the Federal Noxious Weed Act of 1999, it is a federal offense to import Caulerpa taxifolia or transport it across state lines!

The SCCAT team is asking people who think they may have found a new outbreak, not to disturb it. It asks residents to "note as much information as possible about the location where it was found" and to report it immediately to the Southern California Caulerpa Action Team at: (858) 467-2952.