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Green Mussel Invasion In Southwest Florida May Be Controlled By Commercial Harvesting

Chuck Woods (352) 392-1773 x 281

Patrick Baker, (352) 392-9617, ext. 281
John Stevely, (941) 721-6608, ext 239

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TAMPA, Fla.—Unlike the scores of exotic species that have invaded Florida over the years, the newest environmental threat may be controlled in a practical way: serving it as an appetizer.

Commercial harvesting may be the best way to control an invasion of green mussels that continues to spread rapidly along the state’s southwest coast from Tampa Bay to Charlotte harbor, said Patrick Baker, assistant professor with the University of Florida’s Institute of Food and Agricultural Sciences.

“The mollusks are native to the Indo-Pacific, and this is the first time we’ve seen them anywhere in the United States,” he said. “Most likely, ocean currents will spread the mussel further south along the coast toward the Florida Keys.

“One of our biggest worries is that green mussels will somehow become as troublesome and difficult to control as the zebra mussels that have spread from the Great Lakes down the Mississippi River to New Orleans,” he said.

Baker, a researcher with UF’s fisheries and aquatic sciences department in Gainesville, said the green mussels probably found their way into Florida on the hulls of vessels or in ballast water of ships from the Caribbean where the mollusk already is established.

He said the green mussel invasion is another example of how Florida is becoming home to a growing number of “fouling organisms” — exotic plants and animals that grow on piers, boats and other man-made objects. He said the term came from mariners who had to clean their “fouled” ship hulls.

Green mussels, which can exceed 3 inches in length, are unlike smaller native species that normally occur in the same habitat. Florida has other bivalve mussels of all sizes, including some as large as green mussels, but the state does not have large mollusks that act as fouling organisms.

“It’s too early to say how much of a problem the green mussels will become in Florida,” he said. “However, the mussels are already quite abundant, covering pilings on bridges, fouling water intakes at power plants and interfering with clam production.”

Lack of natural predators could be another problem in controlling the explosive growth of green mussels, he said. Flatworms, snails and crabs control other fouling organisms such as barnacles and oysters, but there’s little evidence of predation on green mussels.

Baker, who is working with other UF faculty and the U.S. Geological Survey at UF in Gainesville to learn more about the environmental impact of green mussels, said another concern is that the mollusks will cover crab traps and bags used to culture clams. It’s not uncommon to find as many as 1,000 adult green mussels per square foot, he said.

“When they grow on clam bags, they restrict the flow of water, and they eat the same microscopic algae that clams depend on,” Baker said.

And while green mussels are a worrisome new problem in Florida’s fragile environment, Baker said they are harvested commercially for human consumption in Asian countries such as India, Indonesia and the Philippines.

“To further complicate the picture, the green mussel is often confused with the green-lipped mussel that is cultured in New Zealand and shipped to the U.S. for human consumption,” he said. “The main difference between the two mussels is that the green-lipped mussel is not a tropical species.”

He said the commercial success of green-lipped mussels in New Zealand and green mussels in Asia is driving a growing interest in Florida to start commercial harvesting of green mussels in the state.

John Stevely, UF Sea Grant marine extension agent in Manatee County, said biologists and resource managers would be hard-pressed to see any good coming from a non-native species such as the green mussel becoming established in Florida waters.

“Since green mussels appear to be spreading rapidly, allowing commercial harvest would help control their abundance in local waters and generate some additional income for Florida’s commercial fishing industry,” Stevely said.

“At this point, there is no legal barrier that I know of to harvesting or marketing green mussels in Florida, but there is no market for them either,” Stevely said. “Of course, any mussels harvested would have to come from approved shellfish harvesting areas to ensure they come from clean waters.”

However, he cautioned against eating green mussels because little is known about their safety from a human health standpoint. He said research will determine if green mussels in Florida waters accumulate toxins or harbor parasites.

UF green mussel research is being supported by a $447,000 grant from the U.S. Environmental Protection Agency. Baker, along with Shirley Baker, assistant professor, and Ed Phlips, professor, are working with the U.S. Geological Survey to learn more about green mussels, particularly their impact on native habitats.

Baker said potential negative impacts include competition with the clam industry, displacement of native species mussels, and disease or parasite transmission to native species. The green mussel is likely to spread until it reaches its lowest temperature tolerance.

In closed environments, such as power plants, mechanical or chemical control methods can be employed to reduce or eliminate the species.