Rusty Crayfish (Orconectes rusticus)
This crayfish species is native to streams of the Ohio River basin (Ohio, Kentucky, Indiana, and Tennessee), and since the 1960s has spread across large parts of North America.
In Wisconsin, they occupy a broad range of lakes and streams, and have had pronounced impacts upon northern lakes (Wilson and others 2004). Prior to being banned in 1983, rusty crayfish were widely used as live bait, making bait bucket release a major vector of introductions. Capelli and Magnuson (1983) found that rusty crayfish in Wisconsin's northern highlands lake district colonized areas close to major roads and highly developed lakeshores, indicating the importance of humans in its transport. Once in a watershed, rusty crayfish spread through interconnected waterways, though dispersal is slow relative to many other invaders. Nevertheless, comparison of survey data through time indicates rapid expansion across the state. Comparison of pre-1980 and 2004-06 survey data reveals expansion from 3% to over 50% of sites sampled.
What factors might limit the future distribution of rusty crayfish in Wisconsin? Rusty crayfish do not survive in waters with dissolved Ca2+ concentrations under 2-3 mg/l (Capelli and Magnuson 1983). In Wisconsin, relatively few aquatic systems fall below this level, indicating little potential to limit rusty crayfish distributions.
Rusty crayfish also have a strong preference for rocky substrate, which could influence their presence and abundance. When small, they are consumed by fish like smallmouth bass, though they quickly become too large for predators. Rusty crayfish displace native crayfishes (Capelli 1982), and often reach densities much higher than native crayfishes. Rusty crayfish are both voracious and omnivorous, foraging opportunistically on aquatic plants, detritus, invertebrates, and fish eggs (Lodge and Hill 1994). Invasion is associated with declines in snails, other invertebrates, and littoral fishes, likely through a reduction in aquatic plants (Wilson and others 2004; McCarthy and others 2006; Lodge and Hill 1994). In short, this species has disrupted littoral zones and food chains, and is of growing management concern. Concern is greatest in northern Wisconsin, but based on their rapid expansion during the past decades, this species could be a statewide threat. Perhaps the majority of aquatic ecosystems in Wisconsin are vulnerable to rusty crayfish, though the implications for most regions of the state remain unknown.
Capelli, G.M. 1982. Displacement of northern Wisconsin crayfish by Orconectes rusticus (Girard). Limnology and Oceanography 27: 741-745.
Capelli, G.M. and Magnuson, J.J. 1983. Morphoedaphic and biogeographical analysis of crayfish distribution in northern Wisconsin. Journal of Crustacean Biology 3: 548-564.
Lodge, D.M. and Hill, A.M. 1994. Factors governing species composition, population size, and productivity of cool-water crayfishes. Nordic Journal of Freshwater Research 0: 111-136.
McCarthy, J. M., Hein, C.L., Olden, J.D., and Vander Zanden, M.J. 2006. Coupling long-term studies with meta-analysis to investigate impacts of invasive crayfish on zoobenthic communities. Freshwater Biology 51:224-235.
Wilson, K.A., Magnuson, J.J., Lodge, D.M., Hill, A.M., Kratz, T.K., Perry, W.L., and Willis, T.V. 2004. A long-term rusty crayfish (Orconectes rusticus) invasion: dispersal patterns and community change in a north temperate lake. Canadian Journal of Fisheries and Aquatic Sciences 61:2255-2266.