Invasive rusty crayfish (Faxonius rusticus) are diurnally more exposed than an imperiled native congener

Invasive crayfish can have a competitive advantage over native crayfish due to increased activity in invaded environments, allowing greater resource acquisition. We evaluated whether total exposure time (a proxy for activity, defined as time spent outside of shelter) and behavior differed between imperiled native Faxonius limosus (spiny-cheek crayfish) and invasive F. rusticus (rusty crayfish) from the Susquehanna River drainage in Pennsylvania. We conducted our study opportunistically as part of a larger study in raceways modified to simulate a stream that included a native predator, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis). We recorded video in each raceway and quantified total exposure time and duration of crayfish behaviors. Diurnal total exposure time differed significantly between species, with F. rusticus exhibiting more diurnal total exposure time than F. limosus. However, nocturnal total exposure time was not significantly affected by species. Proportion of time spent engaged in immobile and walking behavior diurnally was dependent on crayfish species, as was proportion of time spent engaging in these behaviors nocturnally. Our results suggest that F. rusticus may have an indirect competitive advantage over native F. limosus due to differences in diurnal activity and behavior.