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Zebra Mussels at
the
The Lake of the Ozarks had an unwanted visitor this summer, one that may never leave. Zebra mussels have arrived! Zebra mussels are an invasive species that are very difficult to control and very expensive to deal with. They can attach to just about anything than enters the water and thus are easily transported from waterbody to waterbody. Originally from the Black Sea region of Eastern Europe, zebra mussels first came to the United States via the ballast waters of ships visiting the Great Lakes. Until this summer this invader had been confined to the Missouri, Mississippi and Meramec rivers in Missouri. Now they are moving into our lakes. We’ve discussed the zebra mussel invasion in several issues of the Water Line (see the website for a complete list), so this article won’t go into great detail about them. What we haven’t discussed much is the ecological impact of zebra mussels. Zebra mussels are very prolific breeders, with adult females producing anywhere from 30,000 to 1.6 million eggs per year. The larval mussels (called veligers) can attach to nearly anything, including docks, boats, plants, people, crayfish and birds. Frequently the mussels attach to each other, which results in large colonies called druses. By forming druses, zebra mussel colonies can grow in three dimensions, not just two, allowing the number of mussels per square foot to skyrocket. A study of some Lake Michigan sites in Illinois and Wisconsin found that zebra mussel densities increased from an average of 14 mussels per square foot in 1991 to a minimum of 5,000 and a maximum of 25,000 per square foot in just one year. The zebra mussel is a filter feeder, with each adult capable of clearing the algae from a quart of water each day. A thousand zebra mussels can thus filter 250 gallons of water each day. As the mussels filter algae out of the water, the water typically becomes considerably clearer. As they process the stuff they filter from the water, the zebra mussels deposit feces and pseudofeces (particles they capture, but can’t ingest) on the lake bottom. The result is that the organisms that rely on free-floating (planktonic) algae will suffer as their food supply is depleted, and bottom-feeding (benthic) organisms will thrive on the fallen scraps and feces deposited by the zebra mussels.
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