Zebra mussels (cluster) threaten freshwater mussels native to St. Croix National Scenic Riverway by blocking their feeding, respiration, and reproductive structures. St. Croix National Scenic Riverway
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Two exotic aquatic species with potential to seriously harm native wildlife are spreading in St. Croix National Scenic Riverway (Minnesota and Wisconsin) and Yellowstone National Park (Wyoming, Montana, and Idaho). In summer 2000, reproducing zebra mussels (Dreissena polymorpha) were found within the lower 16 miles of the St. Croix River as far as Hudson, Wisconsin. The estimated density of the mussels at one location at Prescott, Wisconsin, was 9.3 per square foot (100 per square meter). The zebra mussel, a black-and-white-striped bivalve mollusk, came to North America from Europe. Since it was first discovered in Lake St. Clair in June 1988, it has spread rapidly and is expected to continue to do so throughout North America. The mussel disrupts aquatic ecosystems throughout its range and fouls beaches, clogs water intakes, and damages boat motors. Under the St. Croix River Zebra Mussel Action Plan, adopted in May 2000, the National Park Service and other federal and state agencies are continuing to inform the public about the problems associated with the zebra mussel. The agencies are also inspecting boats and trailers, restricting access to slow the spread of the mussel, and monitoring the spread of the infestation. The New Zealand mud snail (Potamopyrgus antipodarum) was first discovered in Yellowstone National Park in the Madison River in 1974. Localized infestations in the river approached a density of greater than 28,000 individuals per square foot (2,604 per square meter) in 1997. Subsequent investigations by independent researchers documented a rapid spread of this exotic species to the Firehole and lower Gibbon Rivers. Although scientific studies of the snail’s distribution have not been completed, park staff and researchers have observed that this nonnative, invasive species is continuing to spread into the park’s interior. The long-term effects of this exotic species are unknown, but indications are that the snail is impacting the invertebrate community in the rivers it inhabits. Reductions in aquatic insect species diversity or abundance could in turn affect the famous recreational fisheries found in the park. It is not known how the New Zealand mud snail was introduced into the park, but human transport is strongly suspected. The park staff is continuing to monitor the spread of the snail and is conducting a public information campaign to control its expansion. |
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This material is from Natural Resource Year in Review--2000, published by the National Park Service, U.S. Department of the Interior, in May 2000 (publication D-1459)
/YearInReview/yir/yir2000/pages/04_resource_risks/04_08_sidebar_inverts.html
Last Updated: 06/17/2001
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