One mussel, one world of trouble

<i>Editor's note: This is the first in a four-part series examining invasive mussels and how they could affect Lake Tahoe's ecosystem and economy.</i>

Half a billion dollars spent on water-quality environmental improvement programs.

A century of environmental debate about how to protect the blue waters.

A bi-state compact and its two, soon to be three, regional plans to protect the fragile ecosystem of the 1,600-foot deep lake.

And one mussel, brought in through the crevice of a boat, could destroy every effort over the past 50 years to keep Lake Tahoe blue.

"They will jam up drinking-water intakes, they will shed their shells and the beaches would not be usable, they (can) put drag on boats so boats have to constantly be cleaned. It could kill the economy and ruin recreational tourism based on the lake," said John Singlaub, executive director of the Tahoe Regional Planning Agency. "This should be of concern to everyone."

Lake Tahoe's waters are clear of the invasive mollusks for now. But zebra mussels were found in San Justo Reservoir, about 250 miles away from Lake Tahoe, in January of this year. In January 2007, quagga mussels were found in Lake Mead, Lake Mojave and Lake Havasu on the Colorado River. The closeness of these locations has officials on the alert.

Quagga and zebra mussels are close cousins, members of the Dreissena family of shellfish. While the differences between the two are subtle - from appearance to ecological tolerance - the effect is the same. Once introduced into a body of water, these filter-feeders will eat the food and nutrients species higher on the food chain need to survive. In turn, they can destroy an ecological system and collapse an entire food web.

"If you remove the basis of that food web, everything dies," said David Britton, the assistant aquatic nuisance species coordinator for the southwest region of the U.S. Fish and Wildlife Service. "They will eat themselves out of house and home, and then they will start dying off as well."

Ironically, the introduction of quagga or zebra mussels to Lake Tahoe could very well increase lake clarity, said Jason Roberts, an environmental scientist with the California Department of Fish and Game. But that clarity would come at the price of a destroyed ecosystem and a new bloom of blue-green algae - which could turn the water different colors and cause it to take on a bad smell and taste, Roberts said.

"It's not a thing you would want in the lake," Roberts said.

The locustlike creatures can spawn continuously if conditions are amenable - some adult mussels can produce 1 million eggs in one spawning season. Once their life cycle is over, the mussels die off in large batches and their sharp shells can saturate beaches, making them unusable.

"You have accumulated mussels dead in the water all at once that creates quality issues, and have been known to have recreational impacts," said Ted Thayer, the natural-resource and science-team leader for TRPA.

They can attach to most surfaces with their byssal threads - including boat hulls, water intakes, lake floor and even other native mussels.

"I've seem them crawl around like snails," Britton said. "They will move around to get on new substrate."

In their larvelike stage, quagga and zebra can find safe haven in standing water in the bilges, live wells and motors of boats, and be easily transported from one area to another.

If they grow into water-treatment facilities, quagga and zebra mussels can clog pipes and cause millions of dollars in infrastructure costs.

U.S. congressional researchers estimated that the Great Lakes zebra mussel infestation cost the power industry $3.1 billion in the 1993-99 period, with an economic impact to industries, businesses, and communities of more than $5 billion.

Introduced to the United States from Europe in the 1980s, zebra mussels first were discovered in Lake St. Clair near Detroit in 1988. In North America, they have no native predators or natural controls, so a population can grow very quickly, Thayer said.

"They are the poster child for invasive species," Britton said. "They are about as nasty as you can get as far as invasive species go."

And once introduced to a body of water - one mussel larvae is smaller than a grain of sand - can begin an infestation that can not be eradicated, only contained.

"The best we could hope for is control," Thayer said. "Once you have them, you've got them."

History of the quagga and zebra mussels

Zebra and quagga mussels are native Eastern Europe with zebra mussels coming from the Black and Caspian seas and quagga mussels coming from the Dneiper River in the Ukraine.

Zebra mussels were first discovered in the Great Lakes in 1988, and a year later, quagga mussels were discovered in the same area. It is believed they arrived in America via ballast water discharge from boats traveling from Europe.

Europeans have been dealing with the mussels for 200 years by designing industrial facilities with the creatures in mind. The mollusks also have natural predators and controls in those ecologies. But in North America, the mussels can reproduce rapidly when introduced into a new environment because of the lack of control.

The mussels were found in Lake Mead on Jan. 6, 2007, and later throughout Lake Mead's lower basin. Almost two weeks later, they were found in Lakes Mojave and Havasu in the Colorado River. They have also been identified in San Diego County in San Vicente Reservoir, Lake Murray Reservoir, Lower Otay Reservoir, Lake Dixon, and Miramar Reservoir and in Riverside County in Lake Skinner and Lake Mathews.

Most recently zebra mussels found in January in San Justo Reservoir, San Benito County - a mere 250 miles away from Lake Tahoe.

- Sources: U.S. Fish and Wildlife Service and California Department of Fish and Game.

What are quagga and zebra mussels?

Both quagga and zebra mussels are part of the Dreissena family and are close cousins. Differences include physical appearance and ecological tolerance.

They can range in size from microscopic as larvae to about two inches long as adults.

They can life up to five years and can spawn constantly if conditions are amenable producing millions of off spring.

In their larval stage the mussels are free floating and carried with currents. As adults they use byssal threads to attached to hard surfaces, and can detach to move to new habitats.

Zebra mussels can survive in waters as warm as 86 F but survive best in 64 F water. Scientists are researching if quagga Mussels can survive in similar temperatures, but prefer 61 F.

Both zebra mussels and quagga mussels can survive cold waters near freezing, but cannot tolerate freezing - zebras need waters above 54 F in order to reproduce and quaggas need temperatures about 48 F.

To survive the mussels also need low salinity, high calcium content, high PH. Both breeds and survive in low oxygen concentrations.

They prefer to exist in environments with waters moving at low speeds and hard to attach to. Quagga mussels can tolerate living in soft sediments, but zebra mussels seldom do.

Zebra mussels are typically found from just below the surface to about 40 feet. Quagga mussels are typically found at any depth as long as oxygen is available.

Both species prefer to avoid light and are usually found in shaded areas or below the depth that light penetrates water

- Source: U.S. Fish and Wildlife Service