Invasive crayfishes are a global driver of biodiversity loss, reduced ecosystem service provisioning, and economic harm. Two particularly notorious invaders are the red swamp (Procambarus clarkii) and rusty (Faxonius rusticus) crayfishes. F. rusticus is well established across the Laurentian Great Lakes region where it is the dominant crayfish in ecosystems ranging from streams to the Great Lakes themselves. P. clarkii is an incipient invader in the region and there is concern about its spread and potential impacts. In 2015 we discovered what we believe is the first known population of P. clarkiithat overlaps with a population of F. rusticus. If P. clarkii continues to spread it will come into contact with F. rusticus throughout the Great Lakes region, and the outcome of these interactions may be important for future biodiversity across the region. We have conducted lab experiments to test outcomes when these species compete for food and shelter. In the field, we have monitored populations for four years and conducted experiments to determine if predation rates upon these species are different. We will also report results of experimental removals of P. clarkiito reduce risk of further spread.
Results/Conclusions
P. clarkii is established along ~6km of the North Shore Channel, a canal in northern Chicago. At one end of the canal the crayfish community is >95% F. rusticus, and at the other it >98% P. clarkii. No features within the canal to suggest that this pattern is driven by habitat. Four years of sampling (2015-2018) have shown that the range of overlap between these species is stable. We observed during sampling that P. clarkii are both larger (p<0.01) and more aggressive than F. rusticus. In lab experiments P. clarkii outcompeted F. rusticus for food 14/21 times, although this was not significant (p=0.06). To test competition for shelter we simulated a fish attack and recorded which species entered the single shelter. F. rusticus entered the shelter more often (p=0.02), but we observed that P. clarkii responded to the simulated attack with aggression rather than seeking shelter. In field experiments P. clarkii were predated upon at a higher rate than F. rusticus (p=0.049), which we interpret as a result of their reluctance to seek shelter. These results suggest that although P. clarkii is competitively dominant over F. rusticus, this dominance comes from behavior that has a cost in terms of predation.