This post contributed by Adele Conover, a freelance science writer specializing in natural history.
On Halloween night 2005, an anonymous trickster left a jar crammed with zebra mussels on the doorstep of the Charles M. Russell Wildlife Refuge office in Lewiston, Montana. Dr. Eileen Ryce, Montana Fish, Wildlife and Parks Aquatic Nuisance Coordinator, was stunned.
“We assume that the anonymous someone knew what a threat zebra mussels pose.”
However, there’s been no sign of the zebra invader in Montana waters, or unfortunately the perp’s identity. At that point neither the mussel nor its equally notorious cousin, the quagga, had crossed the Continental Divide as far as anyone knew. (Today, despite a recent scare in Flathead Lake, Ryce notes, Montana is still free of these mussels).
Other western states have not been so lucky.
Two years later on January 7, 2007 a sharp-eyed marina employee at Lake Mead (which straddles the Arizona-Nevada border) spotted what he thought was a single zebra mussel attached to a cable anchoring a breakwater. But, the lone mussel was not a zebra, but a quagga that had slipped into the huge lake with nary a splash. It was the first discovery of an invader mussel west of the Continental Divide. Divers rapidly discovered many more quagga, which soon migrated down the Colorado River into Lake Mojave and Lake Havasu on the California/Arizona border. The California-bound Colorado River water flows out of Lake Havasu via the Colorado River Aqueduct to California. By March 2007, much to the alarm of the Metropolitan Water District of Southern California, quaggas were “coursing” down miles of concrete-lined canal surfaces in the California Colorado River Aqueduct system.
“As a remedy,” says Bob Muir, Public Information Officer for the Water District, “we shut down major stretches of the 242-mile Colorado River Aqueduct to dry out the system during the last ten days of July 2007”—to little avail.
Now, according to the Metropolitan Water District’s Microbiology Unit Manager, Dr. Ricardo De Leon, all the southern California reservoirs, lakes and watersheds receiving Colorado River water are infested. (Periodic shut downs of the Aqueduct continue to be part of the Water District’s efforts to contain the quagga.) The Lake Justo Reservoir in Northern California’s San Benito County hosts only zebra mussels. As Lake Justo is not on the Colorado Aqueduct system, biologists believe that this infestation arrived via trailered recreational boats.
The mussels, master filter feeders not only roil ecosystems but clog intake openings and other structures of water systems. Officials in the Midwest and Northeast have spent billions to rid the waters of the scourge yet they persist. The invaders also disrupt the aquatic food chain by vacuuming up zooplankton, phytoplankton, and other suspended organisms in the water column leaving little for other creatures such as fish to eat. A spawning female quagga can produce a million eggs a season. Quaggas siphon up more food than they can eat, ejecting the surplus as “pseudofeces” which drop to the bottom and fertilize benthic flora which then overpopulates. At the same time, sunlight penetrates the newly cleared waters and aquatic plants such as algae photosynthesize and grow. A familiar boom and bust cycle follows. Fish die from lack of food and oxygen, negatively affecting the ecosystem, sport and commercial fishing, boating, and the industries that depend on them, as well as human water supplies and hydroelectric power systems.
Researcher David Wong at the Department of Environmental and Occupational Health, University of Nevada at Las Vegas, says:
“Quaggas have settled in Lake Mead. They attack everything including each other and even another invasive, the Asian clam.”
Quaggas have also displaced zebra mussels in the Great Lakes.
Both mussels arrived in the 1980s in the Great Lakes via the ballast of ships from Northern Europe and the Ukraine. Dr. Carol Stepien, the Director of the Lake Erie Center and Professor of Ecology at the University of Toledo, has used genetic analyses to determine the origin of the invaders and the likely path they followed once they arrived in North America. Stepien’s research indicates that zebras come from multiple non-native northern European populations whereas quagga mussels appear to “trace their ancestry to their native estuaries in the Southern Bug and Dnieper River in the Ukraine.” The quagga mussels that invaded Nevada and California probably came from Lake Ontario, whereas the zebra “marched” west from the St. Lawrence River—both presumably overland via recreational boats.
Foiling their spread has been the aim of The 100th Meridian Initiative, a cooperative effort between local, state, provincial, regional, and federal agencies that was established by the U.S. Fish and Wildlife Service. Western states plagued with the invaders—Arizona , California, Colorado, Nevada and Utah—now have laws that mandate inspection, decontamination, and quarantine of boats to “Stop Aquatic Hitchhikers” as posted signs say. Online surveys and outreach to the news media also spread the word. Surveys indicate that awareness among boaters rose from 2003 to 2008. However, as officials at Lake Mead have pointed out, definitions of boat cleaning differ among boaters —some take their boats to a carwash or wipe them down with a cleaner such as Windex , neither of which does the trick. What does is hosing down every boat part with scalding water of 140 degrees or more. Befouled boats are then required to dry out for about 30 days, depending on their location. The mantra is “Don’t Move a Mussel: Clean, Drain and Dry Your Equipment.” (This is also a video title available on the web.)
Utah’s effort is paying off. In 2010 alone, Aquatic Invasive Species officials interdicted 408,683 boats, decontaminating 11,116. They issued 1581 written warnings, and 341 boaters were required to appear in court.
“We wanted to get ahead of this thing,” says Larry Dalton, the state’s Aquatic Invasive Species Specialist, who recently received the 2010 U. S. Forest Service “Outstanding Partner Against Invasive Species” award.
Mussel-free states such as Montana, Idaho, Washington, Wyoming, and New Mexico have mounted a preemptive strike. Their legislatures have also mandated “inspection-stop authority.” In Oregon—also mussel free—a similar bill is in the works.
At the moment the state’s Aquatic Invasive Species Prevention Program is voluntary, says Rick Boatner, Invasive Species Wildlife Integrity Coordinator. Nevertheless, his “five roaming teams of two managed to inspect 2852 boats in 2010.”
Although watercraft are the usual suspect in transporting these invading mussels from one water body to another, another possible pathway is wildland fire equipment. Fire equipment—tankers, helicopters, fixed wing aircraft, and fire engines—can all harbor invasive larvae. The U.S. Forest Service Intermountain Region now requires that movable equipment be disinfected.
Multiple attempts have been made to rid North American waters of the invaders. The only known success is at Millbrook Quarry, a 12-acre, 90 foot-deep zebra mussel-infested pond in Prince William County, Virginia.
The zebra mussel got there, says Dick Neves, noted mussel expert and professor (emeritus) at Virginia Tech, “because an enterprising diver bent on clearing the water probably introduced it.”
Officials dumped potash—(potassium chloride)—at a cost of $400,000—into the pond. Potash, a water softener, is safe for humans and other animals at certain levels, but toxic to mussels.
No one yet knows of a method to eradicate the invaders once they are established in a large water body. Lake Mead—200, 000 acres, 500 feet deep—is a far cry from Millbrook Quarry pond.
As one observer quipped, “You can’t boil a lake.”
Adele Conover is a freelance science writer currently based in Sunnyvale, California. Her work has appeared in Smithsonian Magazine, The New York Times Science page, The Nature Conservancy, National Wildlife, International Wildlife, Air & Space Mag., Sports Illustrated, and other publications.
Photo credits: Quaggas in Lake Mead, David Kushner, National Park Service; Zebra mussels on boat, David Britton, U.S. Fish & Wildlife Service; Billboard, Aquatic Nuisance Species Task Force