AUTHORS: John F. Bieber, Loyola University Chicago; Ivàn Beck, Colorado College; Reuben Keller, Loyola University Chicago
ABSTRACT: The Chicago River represents a system that is at the edge of several invasion fronts; two of which are the invasive crayfish P.clarkii and F. rusticus. For years, these populations have remained in distinct areas of the Chicago River with little overlap, however; the factor(s) that limits their spread is not known. This project used complimentary field and lab experiments to investigate how stress levels (measured via hemolymph glucose) differed among the populations along a gradient in the Chicago River to inform where populations are in the river.
For the field study, we trapped crayfish in the Chicago River and immediately drew hemolymph from captured individuals. We hypothesized that stress would be the greatest for P.clarkii near Lake Michigan, where populations have not yet been found, and simultaneously would be the lowest for F.rusticus as they are established in Lake Michigan.
In the lab study, we collected P.clarkii along with water from the area where they were captured for holding in lab. Crayfish acclimated in lab before the tanks were filled with Lake Michigan water, and hemolymph was collected after a 90 min period. We hypothesized that P.clarkii populations near Lake Michigan would show lower relative stress to immersion in lake water compared to individuals further downstream and compared to individuals that were not flushed with lake water.
Interestingly, we found that individuals further downstream exhibited elevated glucose compared to individuals closer to Lake Michigan, and our lab studies showed that immersion in Lake Michigan water reduces stress compared to individuals without immersion. Collectively, our results suggest environmental contaminants may be driving the distribution of crayfish. Additionally, this work highlights the importance of considering physiology when managing an invading species.
