Biologists Score Rare Victory Under the Sea

A leafy, emerald-green algae with the ability to crowd out marine life has been eradicated from a harbor in Huntington Beach and a lagoon in Carlsbad, marking the first time marine biologists have been able to defeat the so-called “killer algae.”

The fast-spreading algae has ruined fisheries and clogged popular scuba diving sites in the Mediterranean. Marine biologists feared it could do the same if let loose in Southern California’s ocean waters.

“There was real concern that it would get out into the open coast,” said Bob Hoffman, a biologist with the National Marine Fisheries Service, which led the fight against the algae. “It doesn’t even make good fish food.”

For the environmental community, it’s a rare happy ending. Global successes on knocking out exotic marine pests can be counted on one hand.

“We used to say it was impossible to do these things,” said James T. Carlton, professor of marine sciences at Williams College in Massachusetts. Carlton visited Huntington Harbour and Agua Hedionda Lagoon in Carlsbad soon after the invasive plant was spotted.

The successful algae eradication “gives us hope,” he said.

The algae, called Caulerpa taxifolia, is native to Australia and commonly used in saltwater aquariums because it’s colorful and easy to grow. But when released into the ocean, one stem, root or leaf can start growth that will quickly crowd out native plants and bottom-dwelling marine animals.

Wildlife officials believe the two Southern California outbreaks were caused by people dumping home aquariums into storm drains or the ocean.

In most cases, by the time biologists discover an invasive species, it’s too widespread to corral. Governments worldwide have spent hundreds of millions of dollars trying to keep non-native plants and animals from spreading.

Last month, scientists discovered New Zealand mud snails in four Southern California streams. The tiny gastropods, one-third the size of a housefly, have been found in 10 Western states. They can reach concentrations of hundreds of thousands per square yard and consume large amounts of food that otherwise would feed other wildlife. So far, scientists have been unable to get rid of them.

When it came to Southern California’s two algae outbreaks, marine biologists were careful not to repeat mistakes made in the Mediterranean.

There, off the coast of Monaco, wildlife officials discovered a patch of algae that was smaller than the one found in Carlsbad. “You could swim around it in a minute,” Carlton said.

But rather than acting immediately to keep the plant from spreading, the problem was passed from one agency to another. Years went by and the patch turned into a lawn, the lawn turned into a football field and so on. Wildlife officials say there’s no hope of getting rid of it.

“It’s pretty much there forever,” Carlton said. “It’s turned once very diverse areas into what essentially looks like AstroTurf, a monoculture of green.”

The algae has affected tourism too, Carlton said, because “nobody wants to scuba dive over a green carpet.”

In Southern California, once wildlife officials learned they were dealing with Caulerpa, they launched a $7-million eradication effort. Within two weeks of the algae sighting in Carlsbad, divers carpeted the ocean floor with plastic tarps as large as an acre. They pumped liquid chlorine and placed chlorine tablets under the tarps to poison the plant. In the years that followed, divers surveyed both sites for algae regrowth and found none.

The tarps have been left in place to ensure the algae will not grow back. Meanwhile, new ecosystems, including eelgrass and clams, have grown on top of the tarps, which caused some debate over whether the plastic should be left in place. Divers, however, will begin removing the tarps in September.

Southern California’s success over the algae could become a model for handling small outbreaks elsewhere in the world. Marine biologists said they were fortunate that both algae infestations occurred in calm lagoon waters where there was little wave action to stir up the tarps.

To keep winning battles like these against invasive species, marine biologists say they need the public to help.

“There will be another invasion, but it’ll be found by a fisherman, a bait collector or a scuba diver,” Carlton said. “The conversation starts with ‘I’ve been walking this beach all my life and I’ve never seen this before...’ And that’s what we want to hear.”