INVESTIGATING THE FACTORS MODULATING SPECIES INVASIONS AND DISEASE OUTBREAKS 
IN THE UPPER MISSISSIPPI RIVER 

Gregory J. Sandland and Benjamin A. Walker

Department of Biology, University of Wisconsin La Crosse, La Crosse, WI 54601

Aquatic invasive species are rapidly altering the structure of native 
communities across North America, which has important consequences for 
species diversity, conservation policy, and ultimately, national economics.  
One of the key hotspots for aquatic invasions has been the Great Lakes system 
where over 50 species have been introduced over the last 30 years.  Bithynia 
tentaculata is an invasive aquatic snail that has recently spread from the 
Great Lakes into the Upper Mississippi River.  Range expansion has generated 
2 disconcerting patterns in the river: First, the snails appear to dominate 
the mollusk community, and second, the snail transmits exotic parasites that 
kill waterfowl by the thousands.  Unfortunately, even though B. tentaculata 
and its parasites are directly disrupting general ecosystem stability and 
economics in the Upper Midwest, little is actually known about the factors 
responsible for snail colonization and parasite transmission.  Using a series 
of field surveys, semi-natural experiments and laboratory manipulations we 
are attempting to 1) determine how competition and infection influence B. 
tentatculata establishment, and 2) understand the role that other aquatic 
species play in transmitting these exotic parasites to birds.  Preliminary 
data suggest that native aquatic species may be extremely important in exotic 
parasite persistence and transmission to waterfowl.  Results from this 
research will instrumental in the development of management models aimed at 
curbing the spread of this invasive host-parasite association.   

Keywords:  Bithynia tentaculata, competition, infection influence, Upper 
Mississippi River, parasite transmission, waterfowl