Role of abiotic factors on native crayfish behavioral defense against invasive rusty crayfish (Orconectes rusticus)

Background/Question/Methods

Many of the characteristics indicative of an invasive species are found in the rusty crayfish (Orconectes rusticus): high abundance, high dispersal rates, high genetic diversity, and nonspecific habitat requirements. Within the Upper Susquehanna River Basin, NY, rusty crayfish have colonized some river sections while avoiding others.  Possible explanations for the patchy distribution of rusty crayfish include, (1) variation in abiotic factors tolerated by rusty crayfish, (2) variation in native crayfish behavioral responses to rusty crayfish, and (3) multiple anthropogenic introductions of rusty crayfish.  Previous studies have found differences in rusty crayfish dispersal, habitat use, and ultimately invasion risk under different abiotic conditions, but few have evaluated behavioral responses of native crayfish toward rusty crayfish in the natural environment.  We hypothesized that native crayfish behavioral response to rusty crayfish differs across various abiotic environments.  Four sites were selected, 1 site where rusty crayfish were absent and 3 sites where rusty crayfish were present.  Fifteen-minute behavioral trials between native and rusty crayfish were video recorded and behaviors were scored using a modified ethogram.  We used non-metric multi-dimensional scaling (NMDS) on abiotic factors and tested for relationships between behavioral scores and NMDS dimensions.   

Results/Conclusions

Proportion boulder, pH, and water depth showed a strong negative association with Dimension 1, while water temperature showed a strong positive association.  We found that display behavioral scores and total behavioral scores (display plus agonistic behaviors) were related with Dimension 1.  These relationships suggest that abiotic environments may influence native crayfish behavioral responses to rusty crayfish.  Positive Dimension 1 values, or high water temperature, low proportion of boulder, low pH, and shallow water were indicative of unsuitable habitat for rusty crayfish.  Overall, the patchy distribution of rusty crayfish may be caused by behavioral interactions with native crayfish within certain abiotic environments.  Future studies are necessary to evaluate the tolerance of rusty crayfish to different abiotic environments and multiple anthropogenic introductions of rusty crayfish as additional explanations for the patchy distribution of rusty crayfish in the Upper Susquehanna River Basin.