A long-term rusty crayfish (Orconectes rusticus) invasion:: dispersal patterns and community change in a north temperate lake

Rusty crayfish (Orconectes rusticus) were first observed in Trout Lake, Wisconsin, in 1979 and took 19 years to completely disperse around the littoral zone, advancing at an average rate of 0.68 km(.)year(-1). With the invasion of rusty crayfish, we found that fishes that share prey taxa with crayfish declined in numbers over time, but piscivorous fish species did not change in abundance. Snails declined from >10 000 to <5 snails(.)m(-2) in one of the first invaded areas. Mean abundance of Odonata, Amphipoda, and Trichoptera decreased significantly lake-wide. Resident crayfish species nearly disappeared, although total crayfish abundance, driven by high abundances of rusty crayfish, continued to rise. Submerged macrophyte species richness declined by as much as 80% at some locations. Together these responses demonstrate dramatic long-term changes in the littoral zone biota of Trout Lake. Continued invasions of similar lakes in the region suggest that these impacts are occurring on a region-wide basis with potentially irreversible effects on communities and ecosystems. Only through long-term natural experiments such as this study can researchers ascertain the full extent of invasions and their impacts on community and ecosystem process that respond at spatial and temporal scales not captured in mesocosm studies.