The great lakes are imperiled by two species of great concern: The red swamp crayfish (Procambarus clarkii) and the amphipod ‘scud’ (Apocorophium lacustre). Red swamp crayfish have been found inland and within connected waterways of the Great Lakes; scud has recently spread throughout the Mississippi River Basin and is now within 100 river kilometers of the Great Lakes. Scud and red swamp crayfish can be associated with declines in habitat quality and species diversity, highlighting a need to prevent further dispersal. Both invaders can utilize the Chicago Area Waterway System (CAWS) which is a passageway between the Mississippi River Basin & Great Lakes Basin. In recent years each respective population has not advanced further upstream. Prior work in other taxa has shown that the reduced water quality may serve as an invasion barrier; however it is not known if invertebrates respond similarly.
To understand if water quality can be a barrier, we first conducted experiments to determine how scud respond to different water qualities, including water from the CAWS. We found that water from the CAWS led to a 20% reduction in scud survival over 96 h. Second, we conducted complimentary field and lab experiments to investigate how stress levels (measured via hemolymph glucose) differed among red swamp crayfish populations in the CAWS to inform how water quality can influence distribution. We found that individuals further downstream exhibited glucose levels that are 50% higher than individuals closer to Lake Michigan, and our lab studies showed that immersion in Lake Michigan water reduced stress by 200% when compared to individuals in CAWS water. Collectively, our results suggest environmental contaminants may be impacting the distribution of red swamp crayfish and scud. This work also highlights the need to understand physiology of organisms when managing an invader.