BY LAND AND WATER THEY GO:  AQUATIC SNAILS IN THE SYSTEM.  ARE THEY NATIVE, 
EXOTIC, INVASIVE OR JUST GREAT BIO-INDICATORS?  

Byron N. Karns1 and Ellen Strong 2. 
St. Croix National Scenic Riverway1 National Park Service  P.O. Box 708  St. 
Croix Falls, WI  54024; University of Minnesota2 , Department of Fisheries, 
Wildlife and Conservation Biology, 100 Ecology Bldg., 1987 Upper Buford Circle, 
St. Paul, MN 55108

The St. Croix National Scenic Riverway is a major tributary of the Upper 
Mississippi River.  The Riverway is a unit of the National Park System and is 
recognized for its outstanding recreational and biological resources, 
particularly the nationally significant richness and abundance of freshwater 
mussels (~40 species).  The diversity of unionids within the Riverway is the 
greatest in the Upper Mississippi watershed.  There is little doubt that the 
assemblage of aquatic gastropods is of similar note.  These faunal groups will 
be severely impacted by a zebra mussel infestation or other exotic invasions.  
Freshwater mollusks are a keystone faunal group of freshwater systems and while 
the unionid mussels in the St. Croix and Namekagon Rivers have been relatively 
well studied, little detailed information is available for aquatic snail 
species. Past surveys and sporadic collecting efforts over the past 110 years 
are sufficient to indicate that snails are indeed present in this system, and 
that snail diversity is typically lower than that of unionids, but with similar 
abundances in suitable habitats. However, no recent data is available to assess 
shifts and/or trends in patterns of snail distributions and abundance.

The questions are thus posed in the face of imminent threats.  The St. Croix 
National Scenic Riverway has remarkable native mussel diversity, so one would 
expect similar snail diversity.  Little or no current information on snails from 
the Riverway is known.  Zebra mussels might spell the demise of species before 
river managers are aware of their presence.  Black carp (Mylopharyngodon piceus) 
are certain to have a negative impact on all the Riverway’s mollusks species.  
Mollusks are experiencing dramatic declines and unprecedented levels of 
extinction as a consequence of habitat degradation from agricultural and 
industrial pollution, damming, invasive species (e.g. New Zealand mud snails, 
Zebra mussels, etc.) and a number of other human mediated impacts (Kay 1995a,b; 
Lydeard et al. In press).  A thriving and diverse molluscan assemblage is an 
integral component and indicator of healthy aquatic/riparian ecosystems. 
Therefore, discovering what snail species are present and where, does the 
Riverway support exotic/invasive species, and what impacts will other 
invasive/native species have on this faunal group is a critical set of questions 
to begin to answer.

The poster will outline the study plan for a survey of aquatic snails on the St. 
Croix and Namekagon during the 2004 field season.  Location information will be 
detailed and previous collections explored for sites to reexamine.  Emphasis 
will be placed on those species which are rare or invasive and what strategies 
might be best to conserve or eliminate species based on this determination.  
Also discussed will be tools that might be used to protect desired species from 
the onslaught of threats, particularly aquatic invasive species.

Keywords:  Aquatic Snails, Inventories, Invasive Species, Endangered and 
Threatened Species, St. Croix National Scenic Riverway.