PS 37-34 - Influences of disturbance on growth and survival of Faxonius marchandi, an Ozark-endemic imperiled crayfish

Abstract: Crayfish are considered keystone species that substantially influence trophic dynamics and aquatic production. Despite their obvious importance, approximately 50% of North American crayfish are imperiled, primarily by the spread of invasive crayfish. Faxonius marchandi (Mammoth Spring Crayfish) is a narrow-ranged endemic occurring only in the eastern portion of the Spring River drainage of Arkansas and Missouri. Genetic results indicate significant differences between two groups of the species, separated geographically between downstream tributaries and headwaters in the drainage. In addition to F. marchandi being rare, imperiled, and isolated, an invasive species, Faxonius neglectus chaenodactylus (Gap Ringed Crayfish), is established in the western portion of the drainage and is spreading. The invader has already displaced native species, presumably through mechanisms related to drought and stream drying, a frequent disturbance in the region. Based on the invader’s dispersal rate, it is possible that F. n. chaenodactylus will reach F. marchandi in under four decades, and it is unknown what will happen to F. marchandi if the two species meet. We used stream mesocosms to examine the (1) effects of invasive species on F. marchandi growth and survival, (2) effects of simulated stream drying on F. neglectus chaenodactylus and F. marchandi, (3) additive effects of invasive species and simulated stream drying on F. marchandi, and (4) differences in growth and survival between the two clades of F. marchandi. Analysis is ongoing, but preliminary results suggest the invader negatively influences F. marchandi growth and survival. Drought seems to negatively affect both species’ growth and survival as well as magnify the negative effects of invasion on F. marchandi. It is essential to understand the effects of drought, invasive species, and their interactions on native crayfish, particularly in the context of a spreading invader and the increased likelihood of intensified drought from future climate change.