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March 2010 cover image 12 Great State Park Walks

Unwelcome Visitors

Invasive zebra mussels can wreak havoc on ecosystems.

By Wendee Holtcamp

One of America’s greatest menaces has arrived at Texas’ doorstep. Texas Parks and Wildlife Department biologists _confirmed that invasive zebra mussels (Dreissena polymorpha) have established themselves in Lake Texoma on the Oklahoma border as of April 2009, and fear they may soon spread through the Red River and Trinity River systems.

Native to lakes in western Russia, the fingernail-sized black-and-white-striped mussels first arrived in the United States via the Great Lakes in 1988. They have since spread throughout many of the river systems east of the Rockies and in recent years have headed west — often hitchhiking on recreational boats.

Named one of world’s 100 worst invasive species by the Global Invasive Species Database, zebra mussels wreak havoc on ecosystems they invade, affecting native fish, mussels, invertebrates and vegetation. The prolific mussels completely coat rock surfaces, lake bottoms and even native mussels, not to mention pipes and intake valves for power plants, dams and other water management facilities.

Photo by Eric Engbretson

Because they’re so prolific, they suck up the lake or river’s nutrients, leading to very clear water. That means more sunlight reaches the bottom, favoring rooted macrophytic plants, many of which are exotic themselves, like water hyacinth. Zebra mussel invasions turn the whole ecosystem topsy-turvy.

Over the past few years, game wardens and boat marina personnel have intercepted several infested boats, but one likely slipped past. In April, a houseboat owner living on Texoma called TPWD fisheries biologist Bruce Hysmith and reported a zebra mussel. They dangled PVC pipe devices in the water that mussels would attach to, if present. By July 30, mussels covered every single one. That was bad enough, but in August, TPWD found three live zebra mussels in Sister Grove Creek, which is a tributary of the Trinity River and is connected to Texoma by a water transfer pipe. The creek feeds Lake Lavon, and if the mussels make it to Lake Lavon, it’s probably just a matter of time before they make it to the Gulf of Mexico.

Once they are established, controlling them becomes costly and intensive. According to the Center for Invasive Species Research, power plants, hydroelectric facilities and water management districts where zebra mussels are established spend $500 million a year fighting the pesky mussels, which can completely clog — or “biofoul” — intake valves, pipes, screens and other surfaces. Control methods include chemicals, high-pressure washing, electrical current, ultraviolet light and draining a water body. The U.S. Bureau of Reclamation found that a strain of the bacteria Pseudomonas fluorescens killed 90 percent of zebra mussels. Unfortunately, none of these methods completely eliminates infestations.

Has anyone anywhere been able to stop the spread of zebra mussels? “Let’s just suffice it to say they have distributed themselves to the Gulf of Mexico from the Mississippi River,” says Hysmith. “They were introduced to Great Lakes region in mid-’80s and had this many years to stop their spread downstream, and nobody’s been able to do it. We’re banking on education.”

The best — and really only — way to slow their spread is for boaters to systematically power-wash their boats after visiting any infested water body, or even one not known to have zebra mussels, just to stay on the safe side. Though zebra mussels can hitchhike on the outside of boats, the microscopic larvae, called veligers, can also come along for the ride in even tiny amounts of water. Completely drying out the boat is the only surefire bet.

So what’s next for Texas? “Our plans are to implement an intensive awareness campaign,” says recently retired TPWD Director of Inland Fisheries Phil Durocher. “Beyond that, we have no plans, but we are discussing the feasibility of boat inspection stations. The problem with Texoma is that it’s in two states and is so large. I’m not sure how effective we could be with stations. We’re evaluating all options.”

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