Archive of Spotlight Feature Articles

Asian invader musseling in on U.S. habitats

Perna viridis will find nation's southern coasts hospitable, Texas researcher says.

By Cindie Powell, Texas Sea Grant

The Asian green mussel, an invasive species that has caused fouling problems at power plants on the Florida coast since it was first discovered there in 1999, would be right at home in Southern California and in most of the Gulf Coast's bays and estuaries if it finds its way to those locations, according to biologist Dr. David Hicks.

Under a grant from the Aquatic Nuisance Species Program of the National Sea Grant College Program, the University of Texas at Brownsville researcher is conducting laboratory experiments on Perna viridis, a bivalve native to Southeast Asia, to determine its environmental tolerances.

"One of the main things we're doing with this research project is to try to predict where this animal may spread in North America - what habitats they can potentially colonize," Hicks says. "In particular, we're interested in whether they will be able to colonize areas of high industrial use like Mobile Bay or the Houston Ship Channel."

The bivalves were first spotted in the United States in July 1999, when the Tampa Electric Company in Tampa Bay, Fla., noticed a previously unknown mussel fouling their plants' intake screens and pipes and contacted Mote Marine Laboratory in Sarasota, Fla., for an identification.

The native range of P. viridis is from the Persian Gulf to the Philippines and Hong Kong. They first appeared in the New World in Trinidad/Tobago in the early 1990s, and moved on to Venezuela, to Jamaica, and then to Florida.

"It's most likely they were moved from Southeast Asia to the Western Hemisphere through ballast water (as larvae) or by some kind of fouling - they've been found on anchor chains and the hulls of international vessels. It could be either one of those ways, but somehow tied to shipping," Hicks says.

So far, the Asian green mussel has been found in the Gulf as far south as Marco Island, just south of Naples, Fla., and northward to Anclote Key, just north of Tampa Bay. On the Atlantic coast, it has been found from just north of Titusville, Fla., to the Georgia/South Carolina border.

(Left) A P. viridis colony can block the flow in pipes like this one, where the animals' presence has reduced a four-inch opening to only half an inch. (Photo by Chuck Traxler, courtesy Mote Marine Laboratory.) (Right) Asian green mussels covered the power plant structure at Tampa Electric Company's Gannon Station in this photo from October 2002. (Photo by Chris Gazinski, courtesy Mote Marine Laboratory)

The Asian green mussel has the rapid growth characteristic of many tropical species. Their maximum life span is about three years, but by the end of two years they can grow to be six and a half inches long. They are old enough to reproduce by two to three months after settlement, and older individuals can release millions of eggs during each spawn.

Hicks, who conducted Texas Sea Grant-funded population studies of the related invasive brown mussel, Perna perna, when it appeared on the Texas coast in the 1990s, has done experiments on P. viridis to determine its temperature limits (between 12 and 32 degrees Celsius, or 54 to 90 degrees Fahrenheit) and salinity tolerances.

"They tend to be fairly resistant - their lower salinity limit appears to be about 15 parts per thousand, which is not all that low - but they can survive in freshwater for upwards of almost two weeks. Their strategy is just to isolate and wait it out. And they recover very quickly after that," he says.

A map of Asian green mussel colonization risk shows the varying degrees of hospitability or inhospitability based on 12 months of seawater surface temperature data (NOAA CO-OPS, 2003) and the mussels' thermal limits of 12 to 32 degrees Celsius. The lightest shading indicates the most hospitable areas. The dots indicate the risk levels for particular locations. Many of the areas indicated as high risk (green circles) in Florida have already been colonized by green mussels, and all Gulf States are subject to invasion by this species. (Map by Dr. David Hicks and Samuel Amoako-Atta) (larger view)

Combining data from his laboratory experiments with existing temperature data from the nation's coastal regions using a GIS database, Hicks and Samuel Amoako-Atta of the Center for Coastal Studies at Texas A&M University-Corpus Christi have developed a map of the continental United States that indicates hospitable areas based on consecutive days of temperatures that are within and outside of P. viridis' tolerances.

Hicks is also doing tests on hypoxia (reduced dissolved oxygen in the water) tolerances and desiccation limits (how long the animals can survive being out of the water).

"They were found - alive - at a truck stop in Minnesota on a boat that was being transferred to North Dakota from Florida," he says. "They were on the hull of the boat, dry, and according to our tests, they can probably withstand that, best case scenario, upwards of two weeks with high humidity and fairly low temperature within their temperature range."

In addition to attempting to predict the Asian green mussel's eventual distribution in North America based on their environmental limits, the second goal of Hicks' research is to find ways of using those limits as the basis for non-chemical control strategies. The mussels can block the flow of water, causing mechanical damage to pumps, reduce heat transfer efficiency, clog condenser tubes, and increase the rate of corrosion in the tubes. The eradication strategies plant managers in Florida have been using up to now have included physically scraping the mussels off and using chlorine treatments, which Hicks says is fairly standard for biofouling remediation.

"There are many corporations that make biocides specifically for removing fouling organisms in not only freshwater but saltwater treatment plants," Hicks says. "We're hoping to get away from some of those types of uses."

LINKS:

Texas Sea Grant College Program
Sea Grant Nonindigenous Species Site
National Sea Grant College Program)
Dr. David Hicks
Mote Marine Laboratory
GulfBase, a Gulf of Mexico database by Harte Research Institute for Gulf of Mexico Studies

Other sites about invasive/nonindigenous species:

invasivespecies.gov
nas.er.usgs.gov

[4/18/05]

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