New map outlines risk of zebra musse...( CORVALLIS Ore. The spread of two in...)

CORVALLIS, Ore. The spread of two invasive alien freshwater mussel species the zebra mussel and the quagga mussel appears to be controlled in part by calcium levels in streams and lakes and a new risk assessment based on water chemistry suggests the Great Plains and American Southwest could be next in line for invasion.

Results of the study were published this week in the online version of Frontiers in Ecology and the Environment, a journal of the Ecological Society of America.

The research team that developed the analysis notes that nearly 60 percent of the country, including the Plains states and the Southwest, is in a high-risk ecoregion, based on calcium levels greater than 28 milligrams per liter of water. About 21 percent of the country including New England, most of the Southeast, and the western portions of the Pacific Northwest are at low (12-20 mg) or very low (less than 12 mg) risk for invasion. And in about 19 percent of the country, surface waters have highly variable calcium levels and conditions may change from one lake or river to another, based on geology.

The good news is that many of these high-risk areas dont have a lot of lakes, said Thom Whittier, a faculty research assistant in the Department of Fisheries and Wildlife at Oregon State University and lead author on the study. However, these mussels seem to be working their way west and becoming established in places where theyve never been seen.

Until 2007, neither mussel species had been found in the western United States, but well-established quagga colonies were discovered earlier this year in Nevadas Lake Mead, and downstream in Lake Havasu and Lake Mojave, as well as the Colorado-California aqueduct. By this fall, they had been found in several reservoirs in San Diego and Riverside counties in California, as well as in Arizona, Whittier said.

Both of these invasive mussel species require more calcium than most native mussels and have
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