COEXISTENCE OF INVASIVE RUSTY (FAXONIUS RUSTICUS) AND RED SWAMP (PROCAMBARUS CLARKII) CRAYFISH IN AN URBAN WATERWAY

Red swamp (Procambarus clarkii) and rusty (Faxonius rusticus) crayfish are two highly invasive and widespread species. A main impact of each species is the extirpation of native crayfishes from the habitats that they invade. In the North Shore Channel (NSC) of the Chicago River these two species have overlapping populations. We have investigated the mechanisms that allow these species to overlap. In lab experiments red swamp crayfish exhibited more aggressive behaviors than rusty (p<0.01), leading to a hypothesis that red swamp would win competition for food. In experiments, red swamp crayfish won 66% of competition trials for a single food item. Next, we hypothesized that the aggression of red swamp crayfish would lead to higher susceptibility to predation by fishes, which are the main crayfish predator in this system. We have used lavage to retrieve stomach contents from 545 fishes in the NSC. We found crayfish in the stomachs of 90 fish, and 88 (98%) of these crayfish were red swamp, while only 2 (2%) were rusty crayfish. Finally, we hypothesized that the higher aggression of red swamp crayfish would lead to them having a higher trophic level in the zone where these species overlap. Stable isotope analysis showed the opposite; rusty crayfish have a higher trophic level than red swamp crayfish in the zone of overlap (t-test, p<0.05). Our results show that red swamp crayfish are predated at much higher rates than rusty crayfish, and that this may offset an advantage of red swamp that allows for coexisting populations of these highly invasive species.

Primary Presenter: Reuben Keller, Loyola University Chicago (rkeller1@luc.edu)

Authors:

Reuben Keller, Loyola University Chicago  (rkeller1@luc.edu)

Grant Dlesk, Loyola University Chicago  (gdlesk@luc.edu)