May 22, 2003 

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Green Menace
March 28, 2003
diver underwater
image: ABC

With spring break on the horizon, vacationing scuba divers across the U.S. should watch for what may be lurking beneath the surface of the water: an invasive alien that swamps all marine life in its path.

Green Desert

Caulerpa taxifolia is a bright green seaweed (or alga) once prized by many saltwater fish-tank owners. When in its natural habitat of warm tropical waters, it grows in small, discrete patches. But if the aquarium strain of the plant—more resistant to cold than its wild counterpart—finds itself in non-native waters, it can become extremely invasive and has the potential to be an ecological threat by dominating entire ecosystems.

The plant can grow up to an inch a day, and reach lengths of almost ten feet. Once it has established itself, there is virtually no stopping it, and its destructive potential is sobering. Quickly forming a dense, Astroturf-like carpeting, it smothers everything underneath it and ruins a once-rich feeding ground for other marine life. The alga also contains a toxin which makes it inedible to most marine herbivores. The result? A green desert.

Rachel Woodfield, a marine biologist who spotted the algae off the coast of San Diego, CA, in the summer of 2000, said in an interview with PBS’s NOVA, “ It has a real insidious, sort of creepy nature. As if it’s some sort of blob that’s taking over the bottom.” Woodfieldand her colleagues knew of the plant’s ability to taking over entire ecosystems. Infestations of Caulerpa taxifolia have been reported in nine different countries, on four continents .

seaside town, southern france
image: ABC

But Europe has been hit especially hard. For almost 20 years, Caulerpa taxifolia has been steadily gaining ground on the Mediterranean seabed, and getting rid of it has not been easy. Trying to rip out the algae will only help it spread because a new plant can regenerate itself from even a tiny broken-off fragment of the main plant. This happens by way of an asexual process called vegetative reproduction, which is a form of cloning.

Eradication Efforts

As a result of the European situation, the U.S. Department of Agriculture banned sales and imports of Caulerpa taxifolia under the Noxious Weed Act of 1999 and the Plant Protection Act of 2000. But that didn’t address the fact that a lot of fish tanks across the country might still house the popular seaweed. Therefore, the risk that it might get released in the wild is still real. And, it seems, this is just what happened. When Caulerpa taxifolia appeared in two separate spots off the coast of Southern California, scientists thought the seaweed had probably escaped from someone’s tank.

As Robert Hoffman of the National Marine Fishery Service told NOVA, “It could have been simply a case of where the individual was cleaning his aquarium in his front yard, in the street, and he had the algae in the aquarium and pieces of it floated down the gutter, got into the storm drain and then were just discharged into the lagoon.”

But regardless of where exactly the plant came from, experts knew they had to act fast and eradicate the plant before it could reach the ocean and spread along the coast.

small piece of algae in fingers
image: ABC

Within days they implemented a radical method, pumping chlorine as strong as household bleach into a tarp that had been placed over the algae patch. A few hours later, everything under the tarp—Caulerpa and all the marine life it covered—was killed.

That method of eradication seems to have worked at keeping the plant at bay in California, where surveys are in place to monitor any regrowth. (So far, no new patches of Caulerpa taxifolia have been found.) But the bleach method can’t be used in the Mediterranean, where the plant has already infested over 30,000 acres of seafloor. On top of being impractical, the resulting scale of wildlife destruction would be completely unacceptable. Other means of destroying the plant are currently under study. For example, one option to reduce the amount of the alga in the Mediterranean is to introduce a slug that feeds exclusively on Caulerpa taxifolia.

In the United States, the threat of Caulerpa taxifolia is not exclusive to California. The seaweed could likely establish itself in a number of warm-water locales. Furthermore, a relative of the algae has recently been sighted off the coast of Palm Beach, Florida. Its name is Caulerpa brachypus, and it is also an aquarium strain . At this point, scientists are studying it to determine just how dangerous this type is and whether it has the same invasive properties as its cousin.

If it does, a plan of action would be necessary to prevent America’s favorite beaches from being next to fall prey to the green menace.

by Lisa Chemery

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