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.
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 PBSâ€™s
NOVA, “ It has a real insidious, sort of creepy nature. As if itâ€™s
some sort of blob thatâ€™s taking over the bottom.” Woodfieldand
her colleagues knew of the plantâ€™s ability to taking over entire ecosystems.
Infestations of Caulerpa taxifolia have been reported in nine different
countries, on four continents .
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.
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 didnâ€™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 someoneâ€™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
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.
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 canâ€™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 Americaâ€™s
favorite beaches from being next to fall prey to the green menace.