Scientists Battle Algae Invader

Scientists donned scuba gear and dived into a murky Huntington Beach lagoon Monday in a high-stakes effort to kill Caulerpa taxifolia, an exotic seaweed that could create an ecological nightmare in Orange County coastal waters if it is not contained.

Just weeks ago, hundreds of patches of the tropical algae were found in a three-acre pond off Huntington Harbour, one of two known as the Seagate Lagoons.

Monday’s dive marked the beginning of a painstaking $300,000 effort to eradicate the stubborn organism.

“This is the defensive lineman of seaweed,� said Mark Doalson, an environmental specialist for the Santa Ana Regional Water Quality Control Board, a state agency. The algae can grow up to 9 feet long, with up to 200 fronds, making it one of the largest single-cell organisms in the world. It can survive 10 days out of the water, and leaving even one millimeter of the algae behind could cause another outbreak.

“If this ever gets to Huntington Harbour, things could get pretty ugly,� said Rachel Woodfield, a marine biologist with Merkel & Associates, a San Diego-based biological consulting firm.

In 1984, the exotic seaweed was accidentally released into the Mediterranean Sea, probably from an aquarium. There, it quickly bloomed into watery forests. The seaweed has harmed tourism and destroyed recreational diving across a large area by killing vegetation, and driving sea life away. The seaweed is so pervasive in the Mediterranean now, it is unlikely ever to be eradicated, said Andrew Cohen, a biologist for the San Francisco Estuary Institute.

The algae found in three infestations--from the Mediterranean Sea to Southern California--are all males, meaning they have cloned after a parent was broken into pieces.

The discovery in the lagoon off Huntington Harbour marked only the second time that the bright-green seaweed has been found on the west coasts of North and South America. In July, officials announced the first occurrence of Caulerpa taxifolia in Carlsbad’s Agua Hedionda--or “filthy water�--lagoon 35 miles north of San Diego. In 1998, thousands of scientists banded together to get Caulerpa taxifolia listed as a noxious weed, making it illegal to import it to the United States, Cohen said.

But the algae still makes its way into the country. The major infestations probably started with something that seemed harmless: someone dumping strands of the seaweed from their aquarium into a saltwater environment, Cohen said.

On Monday, Woodfield and colleague Robert Mooney swam carefully in dark waters. They used two techniques to kill the seaweed. Where individual strands existed, they pulled them out, taking care to remove at least 10 centimeters of material below the root-like rhizoids.

The scientists planted yellow flags wherever they pulled up a strand so they could monitor the location.

In the second method, whole patches were covered with plastic tarps and sealed in with a chlorine “puck.� The chlorine should poison the seaweed, Woodfield said.

The scientists labored in a gloomy, sticky environment. The foul-smelling pond has poor visibility. Flapping stingrays kick up sediment. Numerous fish--like smoothhound sharks, bass, goby and yellowfin tuna--have somehow made their way into the artificial pond.

There’s also guano everywhere, from a variety of seabirds.

The stakes are high. Screens were placed over pipes so that any pieces of seaweed accidentally sheared off could not travel to a nearby lagoon, which connects to Huntington Harbour.

The work could cost the state more than $300,000, Doalson said. The scientists all agree: It’s a good thing only male Caulerpa taxifolia has been found where it doesn’t belong.

“If someone introduced a female [and it survived as well as the male strain], that would be very bad,� Woodfield said. “There would be spores floating out there. . . . There’s no way we could stop it.�

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Poisoning Seaweed

County officials are trying to kill an invasive seaweed, Caulerpa taxifolia, found growing off Huntington Harbor. The weed can’t be cut down because it fragments, and each piece can regenerate into a new plant. Divers will either remove plants by hand or use chlorine to try and poison plant beds.

CAULERPA TAXIFOLIA FACTS:

* Grows to more that nine feet long, with up to 200 fronds per stem.

* Spreads vegetatively, through fragmentation.

* Can survive up to ten days out of the water.

* Spread in Mediterranean by fishing nets and boat anchors.

ON LARGE PATCHES OF CAULERPA TAXIFOLIA

1. Divers place a heavy plastic tarp over the seaweed patch.

2. A chlorine “puck’ is placed underneath tarp, then tarp is weighted down, enveloping the seaweed bed.

3. The tarp is sealed along all the edges and the top is fitted with a vent, to allow release of gas produced during photosynthesis. Without the vent, the tarp might stretch and inflate from the gas--possibly uncovering the seaweed patch.

4. The chlorine poisons the seaweed under the tarp.

Source: Rachel Woodfield, Merkel & Associates

Graphics reporting by HECTOR BECERRA / Los Angeles Times