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INVASION OF THE MOLLUSK

You’ve probably seen the movie: beings from space descending on Earth, taking over the planet. They push us humans and other terrestrial life forms aside as they destroy our environment and remake it into one they find more hospitable.

Of course, that is just fiction. But you might be surprised to learn that here in Texas many of our natural habitats and ecosystems are under threat of assault by creatures from a foreign land. Fortunately, there are things we all can do to help protect the rivers and lakes of the Brazos basin – and the rest of the state - from these invasive species.

Non-native plants and animals can wreak havoc when taken from their habitat and introduced to a new area where there are no natural predators, competitors and diseases to keep their growth in check. In their new home they can spread rapidly, crowding out native plants and animals, threatening biodiversity.

Invasive species can also prove costly. Damage to fisheries, agriculture, forests and other resources as well as monitoring and controlling their spread can also be expensive. Invasives cost the United States about $137 billion each year according to TexasInvasives.org, a public-private partnership formed to manage these pests.

Even seemingly harmless animals can prove tremendously destructive when brought into a new environment. Australia learned this lesson all too well after European rabbits were introduced in the country as a source of food. In 1859, a rancher released 12 wild rabbits for hunting. Within a few years, the prolific bunnies, with few local predators, had grown in numbers into the millions. At one point in the 20th century, the number of rabbits was estimated to be around 600 million. The rabbits devastated local agriculture and stripped away native plants leading to serious erosion problems.

Invasive species can spread to a new environment by a number of means. They can be introduced when people plant non-native plants outdoors for garden ornamentals, range plants for cattle or erosion control. They can also be released in a misguided attempt to control other organisms and they can hitch a ride on ships ballast or with imported nursery stock.

In the case of the hydrilla plant, the Asian native made its way to Texas waters a few years after it was released into the environment in Florida from fish tanks where it had been used as an ornamental plant. According to Texas state officials, the plant has been found in at least 100 Texas lakes, including the Authority’s Lake Limestone.

A stringy plant, Hydrilla can grow an inch a day, quickly overwhelming local vegetation. It creates thick mats that can cover an entire lake potentially causing problems for swimmers and boaters, and lowering dissolved oxygen levels by blocking sunlight to other plants. It can also clog intakes of water treatment and power plants.

At Lake Limestone Hydrilla growth has been cyclical and right now is in decline, said Dwight Mahoney, the Authority area project manager for the lake. Mahoney said the plants have actually benefitted the lake at times by providing a safe home for young, fingerling fish.

“At Lake Limestone, the positive really outweighs the negative,” he said.

But one invasive that could devastate Texas lakes and streams with no known positive attribute is the zebra mussel. This Russian native first came to the United States in the ballast of international ships. In U.S. lakes the tiny mussels have quickly spread causing major declines in local fish, birds and other aquatic species. They also damage watercraft by attaching themselves in large numbers to hulls, boat water systems and air conditioners.

Zebra mussels have proved to be most problematic to people by clogging the water intakes at power and water treatment plants. In April 2009, the mussels were found in Lake Texoma, on the Texas-Oklahoma state line, and in a stream that feeds Dallas-area’s Lake Lavon according to the Texas Parks and Wildlife Department.

Thus far, zebra mussels have not been found in other Texas lakes, including those within the Brazos River basin. Officials say the public is the first line of defense against the spread of zebra mussels, Hydrilla and other nuisance aquatic species. Making sure to clean your watercraft thoroughly after taking it from an infested lake is the key to helping stop the invasives’ spread.

A more thorough cleaning process is needed for zebra mussels, because not only the mussels but their larvae can attach themselves onto a boat – unseen. State officials ask anyone transporting a vessel used on Lake Texoma to another water body to take the following precautions:

  • Clean all vegetation, mud, algae and other debris from the boat and trailer.

  • Drain all water from the motor as well as the live well, bilge, bait buckets and any other compartments or systems that hold water.

  • Dry the vessel and associated equipment for 7 to 10 days from May through October or for 15 to 20 days from November through April. These drying times are approximations, and factors such as cooler air temperatures, higher humidity and whether or not the vessel is kept in dry storage should be considered.

Under the Texas Parks and Wildlife Department and Texas Penal Code, possession or transporting of zebra mussels in Texas is a Class B misdemeanor punishable by a fine of up to $2,000, jail time up to 180 days, or both.

A video showing how to decontaminate a boat can be viewed by clicking here. For more information on zebra mussels and other invasive aquatic species in Texas, click here.