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Presented at the NABS Annual meeting, Athens, Georgia, 2003
in Unionid Ecology
Juvenile density has decreased in select St. Croix River mussel communities over the last 10 years
D.J. Hornbach1, M. Hove1,2, D. Allen1, K. Dietrich1, C. Gonzalez1, and K. Swenson1. 1Department of Biology, Macalester College, St. Paul, MN 55105, 2Bell Museum, University of Minnesota, St. Paul, MN 55108
The diverse mussel community in the St. Croix River is a nationally recognized resource. We quantitatively assessed mussel communities during 2002 at: Interstate State Park, MN; Osceola, WI; Lakeland, MN; and Bayport, WI. These communities have been sampled at various times during the last 10 years. During 2002 we observed 21 species at Interstate State Park, 19 at Lakeland, 13 at Osceola, and 9 at Bayport. Average mussel density during 2002 was highest at Interstate State Park (14.6 mussels/m2), followed by Lakeland (9.3 mussels/m2), Bayport (5.2 mussels/m2), and Osceola (2.6 mussels/m2). Since 1992 total mussel density has declined significantly at Interstate State Park. Also, declines in juvenile mussel density have occurred at these four sites over 10 years. Shell-length frequency diagrams suggest there has been little recruitment or there is low juvenile survival among most dominant species at all four sites. The decline in juvenile density at these four sites is consistent with data from four other sites in the St. Croix River, which suggests that a lack of recruitment or low juvenile survivorship is a system-wide issue. The reasons for the apparent decline in recruitment are unknown but at Interstate State Park there has been increase sediment deposition.
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