Lake Mead
The recent discovery of a destructive, exotic mussel in Lake Mead has put California officials on alert for the invader, which can cause millions of dollars worth of damage to water pipes and foul aquatic ecosystems. The quagga mussels in Lake Mead signal its western arrival, an event that wildlife and water officials have been trying to avert.
The quagga and its close relative, the zebra mussel, have been found primarily east of the Mississippi River, particularly in the Great Lakes. There, 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. 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.
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.
There may be limiting factors, such as water temperature, that could curb the spread of the mussels throughout the lake. 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 fewer nutrients to support the fish food chain. The mussels could compound that problem. Adult mussels can travel by attaching themselves to boats and floating objects while the larvae can drift downstream in the water.
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.
January 18, 2007 6:45 AM | Category: Invasive Species