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Despite park officials' vigilance, exotic mussels invade Lake Mead

January 17, 2007|Bettina Boxall | Times Staff Writer

The recent discovery of a destructive, exotic mussel in Lake Mead has put California officials on high alert for the invader, which can cause millions of dollars worth of damage to water pipes and foul aquatic ecosystems.

The Jan. 6 find of quagga mussels in Lake Mead signals its western arrival, an event that wildlife and water officials have been trying to avert.

"This is the first infestation in the West. That is one of the concerns and disappointments," said Kent Turner, a National Park Service resource manager at Lake Mead, which is just east of Las Vegas on the Colorado River. "It's a big deal."

Until now, the quagga and its equally mischievous and more common close relative, the zebra mussel, have been found primarily east of the Mississippi River, particularly in the Great Lakes. There, massive colonies have clogged water intake and outfall pipes and altered basic aquatic food webs.

It is assumed the quagga arrived in Lake Mead from the Midwest on a boat, the same way they could hitchhike out of Mead into lakes and rivers in California and other neighboring states.

"We're very concerned," said Susan Ellis, invasive species coordinator for the California Department of Fish and Game, which is working with other agencies to increase boat inspections and inform the public of the threat. "They can cause both environmental and economic problems."

Western states have been on guard against the mussel invasion for years. At Lake Mead, there have been several close calls, when zebra mussels were found on out-of-state boats before they were launched into the water.

"Most biologists felt the spread of these mussels across the country would be inevitable," Turner said.

Native to Eastern Europe, zebra and quagga mussels were discovered in the United States about 20 years ago in the Great Lakes and quickly established themselves in the region. Zebras have since spread into river drainages in the southern and eastern U.S., and quaggas have been found in the Mississippi River.

Although only quaggas have been identified so far, park officials say it's possible both types may be in Lake Mead, which is North America's largest reservoir and a popular boating destination for visitors from throughout the country.

Both mussel species are prolific breeders and voracious eaters. They cluster by the millions in dense colonies, feeding on phytoplankton. At one research station in the Hudson River, scientists found the amount of phytoplankton had plummeted by 85% after a zebra invasion.

The mussels filter microscopic food from the water so thoroughly that in areas where they are abundant, the water has gained clarity.

But the suggestion of cleanliness is misleading. As waste from the feeding process decomposes, it uses up oxygen and releases toxic byproducts.

Turner said there may be limiting factors, such as water temperature, that could curb the spread of the mussels throughout the lake.

"How it will play out ecologically remains to be seen," Turner said. "We can still be hopeful that it may not get to densities that have a significant impact on fisheries."

The endangered razorback sucker lives in Lake Mead, as well as several nonnative sport fish such as largemouth bass and threadfin shad.

Since the construction of Glen Canyon Dam and Lake Powell upstream of Lake Mead in the 1960s, there are less nutrients to support the fish food chain. The mussels could compound that problem.

"There is a limited amount of food to go around, and now there is going to be more competition for that food," said Larry Riley, chief of fisheries for the Arizona Game and Fish Department.

Adult mussels can travel by attaching themselves to boats and floating objects while the larvae can drift downstream in the water.

"There's a lot at risk here," Riley added, noting the relative proximity of Lake Havasu downstream of Lake Mead and Lake Powell and the Grand Canyon upstream.

Since the Jan. 6 discovery, the Park Service has sent divers into various parts of Lake Mead, but so far they have found the quagga mussels only in the Boulder Basin a few miles from Hoover Dam.

Although the mussels can be cleaned from pipes, there is no known way of eradicating the invaders. The best officials can hope for is containment.

Whether it's a canoe or a houseboat, it's vital that boaters clean all mud and debris from their craft before transporting them elsewhere, Turner said.

Bob Muir, spokesman for the Metropolitan Water District of Southern California, which imports Colorado River water from Lake Havasu, said the agency was sending divers into the lake to check the intake pipe and was also inspecting boats being launched on its Riverside County reservoir, Diamond Valley Lake.

"We're making an all-out effort to protect our sources of supply from the invasion of these species," Muir said.

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