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Europeans provide ideas for destroyingresilient algae
California joins global assault on killer seaweed
Europeans provide ideas for destroying resilient algae
Monday, January 20, 2003
Hvar, Croatia -- Beneath the surface of Starigrad Bay, the finger-shaped inlet that serves as this Adriatic island's main harbor, the invasion is well under way.
Just off the main ferry landing, the seafloor is carpeted in luxuriant green foliage, a thick meadow of beautiful seaweed stretching uninterrupted as far as the eye can see. The delicate, bright green plants have covered rocks, sand, mud and virtually everything else in their path.
Before 1995, nobody in Croatia had ever seen this voracious tropical interloper, which is toxic to most marine animals and rapidly replaces other sea-bottom ecosystems. In the future, researchers fear, those diving off its Adriatic coast may see little else.
Others fear California could be next.
Dubbed the "killer algae" by European scientists, Caulerpa taxifolia seems to know no bounds. Prized by aquarium owners as an ornamental plant, the seaweed has been unwittingly spread from its home in the tropical Pacific to Europe, Australia and, most recently, Southern California, where authorities are trying to snuff it out before it takes over everything.
"If, God forbid, Caulerpa comes to San Francisco Bay on somebody's boat anchor or (discarded home) aquarium water, there are areas that are probably warm enough to support it," says Susan Williams, director of UC Davis' Bodega Marine Laboratory in Bodega Bay.
PLANT MUTATED IN CAPTIVITY
Caulerpa taxifolia normally grows in small, discreet clusters in tropical Pacific waters, dying if the water temperature drops below 70 degrees. But something happened after specimens of the plant were imported in the 1970s by the Wilhelmina Zoo in Stuttgart, Germany, which displayed the plant in its tropical aquarium.
Somehow, the normally timid plant mutated in captivity, producing a strain capable of surviving for months in waters as cold as 50 degrees. The mutated strain also grows several times larger than its normal tropical size and spreads much faster, capable of colonizing most bottom types.
The Wilhelmina Zoo gave samples of the pretty weed to other institutions throughout Europe. In 1984, an employee of the Oceanographic Museum of Monaco discovered a single square-meter patch of the alien seaweed growing in the sea beneath the museum. Scientists dismissed the escaped seaweed as an amusing curiosity and expected the plants to die over the winter.
Instead, Caulerpa spread far and wide, hitching rides from port to port on boat anchors and fishing gear. Today, it covers 32,000 acres of the Mediterranean seafloor, replacing diverse native bottom habitat from Tunisia to Croatia to Spain.
"For the Mediterranean Sea, it is too late. It can never be eradicated," says Alexander Meinesz, professor of biology at the University of Nice-Sophia Antipolis in France, who first alerted the scientific community to the seaweed's threat. "All of the (near-shore) areas of the Mediterranean will be more or less invaded by this species," he says.
ALGAE 'SPREADS LIKE CANCER'
Caulerpa was carried hundreds of miles across the sea to the Adriatic island of Hvar on the anchor of a passing yacht seven years ago. Now, it covers almost 100 acres of sea bottom and continues to spread.
"It gets bigger every year," laments Ante Zuljevic of the Institute of Oceanography and Fisheries in nearby Split, whose efforts to eradicate the invasive seaweed merely slow its expansion. "Caulerpa spreads like cancer in a human being. Our hope is that we can keep it in check until somebody finds a way to stop it."
Like some B-grade science-fiction alien, Caulerpa has gone global, showing up in bays and estuaries around Sydney and Adelaide in Australia. It also was found growing in a saltwater lagoon in Carlsbad, 20 miles north of San Diego, in July 2000. It has since been discovered in Huntington Harbor in Orange County, 50 miles north of the first site.
U.S. scientists and authorities have advantages over their colleagues in the Mediterranean: They can draw from the painful lessons Europe has learned during its 14-year struggle with the renegade algae.
Europeans have discovered that once Caulerpa gets established in a particular area, it is very difficult to eradicate. Since 1991, French scientists and authorities have tried many methods: smothering the plants with salt, sucking them up with vacuum hoses, uprooting them by hand, and smothering them under tarps. In each case, the algae quickly bounced back.
Fortunately, eradication efforts in Southern California started early. Because both of the affected sites are located in nearly enclosed lagoons, scientists hope the seaweed can be completely wiped out before it spreads to the open ocean and beyond.
"If Caulerpa had to invade, at least these lagoons present a manageable situation," says Williams, the UC Davis scientist who has been closely watching the project. "We're very concerned that they will get out of these lagoons."
COMPANY MAKING HEADWAY IN STATE
Keith Merkel, head of Merkel & Associates, the company that is trying to get rid of the Caulerpa, says the firm made eradication its top priority early on. European scientists told them, "Don't mess with this stuff. Your single focus should be to kill it."
The San Diego company covers Caulerpa stands with tarps, then kills them by applying chlorine underneath the covering. Rachel Woodfield, the head of the eradication program, says the method appears to be working. In her last underwater surveys of the Carlsbad infestation site, she found only a 4-square- foot area of Caulerpa, down from 11,000 square feet initially.
"The battle is by no means won," Woodfield says, noting that all it takes is a single Caulerpa fragment to spark an infestation. "We want to find no Caulerpa at all for several years before we can declare victory."
Susan Ellis, invasive species coordinator at the California Department of Fish and Game, says that preventing new introductions will require the cooperation of aquarium hobbyists and the businesses that sell marine plants to them.
"It's clear from the type of strain that this Caulerpa came from the aquarium trade," she says.
Caulerpa taxifolia and other members of the Caulerpa genus are extremely popular among aquarium hobbyists, who use them as an ornamental plant. As recently as 2001, the invasive Mediterranean strain of Caulerpa was being sold by 10 percent of Southern California's saltwater aquarium stores, according to a survey by biologists Steven Murray and Susan Frisch of California State University at Fullerton.
"In many of the stores we visited, 'Caulerpa' was used as a synonym for seaweed," Murray says. More than half the stores sold some variety of the Caulerpa genus, and 95 percent stocked "live rock," pieces of stone containing live marine organisms, including seaweed fragments.
But aquarium hobbyists are passionate about the Caulerpa genus, which comprises 73 species, many of which are difficult to tell apart, even for experts like Murray and Williams. When state legislators proposed a bill banning possession or sale of the entire genus, they were swamped with hundreds of letters,
e-mails, and phone calls from angry aquarium owners.
"We had a nationwide outcry," recalls David Weaver, a legislative assistant to Assemblyman Tom Harman, R-Huntington Beach (Orange County), who introduced the bill. "Their message was that banning the entire genus would have dire effects on aquarium owners."
In the end, legislators banned only nine Caulerpa species: three known to be invasive and six look-alikes. Williams is concerned that the law will be unworkable because of the difficulty of telling Caulerpa species apart. "There is a scientific consensus that all Caulerpas should be banned from the aquarium trade," she says. "The risk is just too great."
Woodfield, speaking on a cell phone from a boat on the infested Carlsbad lagoon, urged aquarium hobbyists not to release plants and animals into nature,
especially Caulerpa. "If you have caulerpa, get rid of it," she says. "Get it out of your tank, put it in a plastic bag and freeze it, and throw it away."