Étouffée, Anyone?

Found this guy just before lunchtime today:

Rusty Crayfish (Orconectes rusticus), Waukegan Beach,
Lake Co, IL 4/10/2014

Well, okay, just before some lucky gull's lunchtime! This is a Rusty Crayfish (Orconectes rusticus). It's an interesting example of the issue of invasive species. It's native to North America, but only to the middle parts of the Ohio River drainage, in Indiana, Ohio, Kentucky, and Tennessee. However, either as bait or as a stowaway, it reached Illinois in 1973 and it's now found across much of the continent. As it moves into new areas, it tends to out-compete native species of crayfish (there are over 300 species of crayfish native to North America, with the greatest diversity in the Southeast).

Exactly how O. rusticus displaces its congeners has been a matter of some debate: Garvey & Stein (1993) examined the size of the claws, since those are used in aggressive encounters. (1) Hill, et al. (1993) looked instead at the questions of growth and survival, finding that O. rusticus grew faster and survived better than the two species it's been out-competing in Wisconsin, O. propinquus and O. virilis. (2)

What seems to be less of a debate, though, is the effects on the rest of the ecosystem in an invaded body of water. Wilson, et al. (2004) and Lodge & Lorman (1987) both found profound impacts on plant mass, as well as severe declines in numbers of snails and other macroinvertebrates, as well as in those fish that eat invertebrates. (3,4) And Lodge, et al. (1994) experimentally demonstrated the existence of trophic cascades originated by O. rusticus. (5)

There was an awful lot of natural history hiding behind that seagull's lunch. Kind of makes me wonder about this evening's pesto!

(1) Garvey, J. E., & Stein, R. A. (1993). Evaluating how chela size influences the invasion potential of an introduced crayfish (Orconectes rusticus). American Midland Naturalist, 172-181.

(2) Hill, A. M., Sinars, D. M., & Lodge, D. M. (1993). Invasion of an occupied niche by the crayfish Orconectes rusticus: potential importance of growth and mortality. Oecologia, 94(3), 303-306.

(3) Wilson, K. A., Magnuson, J. J., Lodge, D. M., Hill, A. M., Kratz, T. K., Perry, W. L., & 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(11), 2255-2266.

(4) Lodge, D. M., & Lorman, J. G. (1987). Reductions in submersed macrophyte biomass and species richness by the crayfish Orconectes rusticus. Canadian Journal of Fisheries and Aquatic Sciences, 44(3), 591-597.

(5) Lodge, D. M., Kershner, M. W., Aloi, J. E., & Covich, A. P. (1994). Effects of an omnivorous crayfish (Orconectes rusticus) on a freshwater littoral food web.Ecology, 1265-1281.