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Public Radio's Environmental News Magazine (follow us on Google News)

Killer Algae

Air Date: Week of

Researchers have discovered a stealth invader off the coast of San Diego: non-native algae that grows so fast it can muscle out most other plant species. It’s already wreaked environmental havoc in the Mediterranean. But as Erik Anderson reports, California scientists hope to eradicate the weed before it has a chance to do serious harm in their territory.


TOOMEY: Biologists in Southern California hope quick action will help wipe out an aggressive algae that's threatening the region's coastal ecosystem. The underwater plants, a popular decoration for home aquariums, was recently discovered in a San Diego County saltwater lagoon. Left unchecked, biologists say the algae could devastate the native plant and animal life there. From member station KPBS in San Diego, Erik Anderson reports.


ANDERSON: A battle is being waged in a large saltwater lagoon in San Diego County. The enemy is a biological bulldozer, a quick-growing single-celled algae that threatens to overwhelm native underwater plants. Agua Hedionda is a sheltered body of water that snakes inland from the ocean. Although it's surrounded by homes and straddled by the always busy Interstate 5, the lagoon is a biological smorgasbord. Its muddy coast is alive with tiny bugs, worms, and plants. Birds flock here to eat, rest, and raise their young. Underwater, biologist Adam Bailey says delicate eel grass serves as the foundation for a complex food web that nurtures sea bass, halibut, and even lobsters.

BAILEY: A lot of the water depth is only about six feet or so. And if you hover right around three feet, you have to kind of swim through the eel grass and part it as you go. You see the sediment below you and you see just the water column on top of you with all the fish nibbling and eating and feeding.

ANDERSON: But in June, divers noticed something new. An eel grass in the western part of the lagoon had changed. Instead of the wavy four-foot-tall grass, a huge patch of the muddy floor was carpeted with a short, dense, fluorescent green plant. Divers bagged a portion of the weed and brought it to biologist Rachel Woodfield.

WOODFIELD: I definitely did not recognize it as anything I'd ever seen before. And knew there was probably a problem with it.

ANDERSON: Woodfield dragged out an old biology text. The plant found in the lagoon looked like an algae common to warmer tropical waters: Caulerpa taxifolia.

WOODFIELD: It's got a lot of different shapes on it. It's got a stem, and it's got a frond, and it's got these sort of, they're not real true roots, but they sort of look like roots. And a real complex structure.

ANDERSON: Southern California waters should be too cold for Caulerpa. The plant is indigenous to tropical waters, but Woodfield knew that a similar plant had invaded the northern Mediterranean. So she logged onto the Internet looking for more information.

WOODFIELD: Sure enough, as the picture unrolls on the screen, it's like holy cow, this is what we've got. We are potentially in some really big trouble here, and it took a while for the alarm to really set in of the potential for what could happen.

ANDERSON: Caulerpa's devastating potential has already been realized in the Mediterranean. Since a three-square-meter patch was discovered off the coast of Monaco in 1984, the plant's territory has grown exponentially. It now covers 10,000 square meters of underwater habitat from Spain to Croatia, and it continues to expand. Most of the other plants are simply overrun by the fast-growing fronds. And to make matters worse, the weed contains a chemical that repels other sea creatures. The end result is an underwater landscape dominated by Caulerpa. Efforts to contain Caulerpa so far have proven fruitless in the Mediterranean. Divers have tried vacuuming it off the ocean bottom, but it grows back. Chemical treatments have had a minimal impact. Even cutting off sunlight failed to control Caulerpa's explosive growth. That scares California biologists like National Marine Fisheries service scientist Bob Hoffman.

HOFFMAN: An uncontrolled beast is what it is, that just -- I mean, it's one of those science fiction B-movies, where this blob just expands uncontrollably. And that's what exactly this thing does.

ANDERSON: Hoffman says the plant probably got a foothold in the water thanks to a saltwater aquarium. He speculates someone either dumped a tank directly into the lagoon or cleaned out their aquarium in their back yard, near a storm drain that feeds into the body of water. California officials hope quick action keeps this from becoming a disaster. A number of federal, state, and local agencies are already working together to eliminate the invader. That's a good sign for University of Tennessee biologist Dan Simberloff. He was part of the team that last year convinced federal officials to ban the plant in the United States.

SIMBERLOFF: The fact that it appears so far to be restricted to this lagoon suggests to me that it could quite possibly be eradicated. I'm convinced it could have been eradicated in the northwest Mediterranean, but the French government botched it. They refused to try. No agency would take responsibility for the attempt, and so it grew and grew and grew. Now it's so large they can't remove it.

ANDERSON: Because the plant reproduces by breaking off and drifting to new locations, divers have encircled a half-acre section of the lagoon basin. Buoys hold up a huge underwater silk net that isolates the weed. Biologist Rachel Woodfield, meanwhile, has tested a number of different algaecides on Caulerpa and found that chlorine kills it. She plans to first cover the weed with heavy plastic tarps weighted down with steel rods and rocks. Woodfield hopes that will protect other plants and animals. Then divers will treat the area underneath the cover.

WOODFIELD: Now we need to figure out how best to apply it. So we're trying squirting it as a liquid, containing it as a solid, that kind of thing.

ANDERSON: Local officials are optimistic the eradication effort will work. But they also say that won't end the Caulerpa threat along the California coast. While this outbreak occurred in a sheltered San Diego lagoon and was noticed quickly, the next may happen in the open ocean. That would make control a much more difficult proposition. For Living on Earth, I'm Erik Anderson in San Diego.



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