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organisBS have had dramatic ecological iapacts on biodiversity and the 

 survival of native species. 



These patterns of intensive invasions lead to the prediction that 

 additional invasions are now occurring, and will certainly occur in the 

 future, if the hypothesized mechanisa of transport (ballast water and 

 sedlaents) continues — that is, if the faucet is not shut off or the 

 flow significantly reduced in some manner. 



These global invasions have sparked a good deal of discussion as to why 

 ballast water would play a greater role now than before in the dispersal 

 of non-indigenous species. Unfortunately , predictions of what species 

 will invade, and where and when invasions will occur, remain one of the 

 more elusive aspects of biological Invasion science. Why, for example, 

 the zebra mussel successfully colonized Lake St. Clair and Lake Erie 

 about 1985 (to be discovered two years later in December 1987), remains 

 unknown. A variety of hypotheses, relative to changes in donor region, 

 new donor regions, changes in the recipient region, invasion "windows of 

 opportunity", changes In the dispersal vector and inoculation frequency, 

 and stochastic massive inoculation events, all seek to contribute to our 

 understanding of why invasions occur when they do. 

 Shipping from domestic and foreign ports can also transport non- 

 indigenous organisms to inland ports in the National Waterway System. 

 Ocean-going deep-water vessels penetrate into major U.S. waterways other 

 than the Great Lakes, transporting freshwater or brackish organisms up 

 river as fouling or ballast water organisms. These sites include the 

 Hudson River, the Chesapeake Bay, the Mississippi River, the San 

 Francisco Bay-Delta region, and the Columbia River. 



Prom these ports commercial barges, ferries and recreational boats can 

 transport non- Indigenous species well above areas navigable by deep 

 water vessels. In the heartland barge and other vessel traffic can move 

 organisms as far north as St. Paul -Minneapolis on the Mississippi River, 



