ra mussels, most of the effects are negative. They disrupt the natural food chain, causing losses to commercial fishermen. For instance, it is thought that somehow the zebra muscle is causing the disappearance of a small shrimp-like creature, the diporeia, which is at the bottom of the food chain, reducing food available for its predators, and ultimately for trout and salmon, which are highly commercial fish (Long, 2001). In Lake Ontario, the presence of the goby is feared to have an impact on the $100 million a year commercial fishing industry (Walker, 1999).
This paper will look first at the effects of the zebra mussel, then the weed Eurasian watermilfoil, and finally the fish round and tubenose goby, all of European origin. It will look at their entry into the United States, their spread, attempts to halt their invasion, and the impact they have had environmentally and economically. The conclusions will give some suggestions of what needs to be done to prevent further invasion of the United States by nonindigenous aquatic species.
Zebra mussels (Dreissena polymorpha), gray-and-white striped fresh water molluscs, were first introduced into American lakes in the mid-1980s from the ballast picked up in the Caspian Sea and discharged from European ships. They are a native of Russia, and settle on hard surfaces, plugging up the intake pipes of power plants and fouling bridges, ship bottoms and dams (Weeding, 1994). Since their introduction, they have spread rapidly and have spread through all the Great Lakes and eight North American river systems. Zebra mussels were first detected in North America little more than a decade ago, but since that times they have earned a mixed reputation. On the one hand, they have caused an economic problem because they tend to clog and damage water-intake and drainage pipes in the Great Lakes Region, and have been implicated in the disappearance of a tiny shrimp-like creature, diporeia,...