There has been an incursion into the sovereign territory of the United States of America. The Zebra mussel, an animal much akin to the clam, has colonized nearly every hard surface in the Great Lakes area, and many rivers and streams attached to them. These invaders arrived on ships from England, pumped out through the ballast. Zebra mussels are from a different environment (England), thus they are classified as an exotic species. These pesky animals threaten the entire Great Lakes ecosystem.
             The invasion has created many problems for the local ecosystem. First of all, Zebra mussels take the food for which native species already compete. Each mussel consumes about a liter of different types of plankton. Small fish lose their food, and their numbers dwindle. Big fish no longer have small fish to eat, and the entire food chain is disrupted. Now that the natives don't have enough food to go around, mortality rates are going up and they are starting to die out. Another problem they've created is clogging on industrial units. They reproduce en mass and attach themselves to anything they find, including docks, boat ramps, and waste pipes. All the industries in the area now have to worry about scraping these mini-invaders off. Yet another problem they've created is contaminated drinking water. The intake pipes in Lake Michigan and elsewhere are covered with mussels. Without being removed, they contaminate water and move on to clog up city pipes. Still another problem is their colonization of rock reefs. With the mussels being several inches deep in places, their waste is poisoning the area and fish that would normally lay their eggs there must look elsewhere for nesting areas. Now natality is down and mortality is up. A final problem they cause is damage to property. By latching onto boats and other floating objects, they can and will damage them. They cause innumerable problems, so now the
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