PS 37-33 - Rusty crayfish (Faxonius rusticus) interactions with benthic macroinvertebrates in the Monocacy River

Abstract: The rusty crayfish (Faxonius rusticus) is an invasive species known to alter benthic macroinvertebrate community structure in lentic ecosystems through predation. However, its impacts on lotic ecosystems are not as well understood. Since 2007, Faxonius rusticus has established its presence as a dominant crayfish species in certain areas of the Monocacy River. To investigate its impacts on benthic macroinvertebrates, I analyzed macroinvertebrate data from sites in the Monocacy River, with and without an established presence of Faxonius rusticus. Macroinvertebrates were sampled in the years 2016 and 2021, and after macroinvertebrates were identified and enumerated, we used Shannon Diversity Index (H), density, and biomass as response variables. Interestingly, we observed no significant differences in these variables or taxonomic composition between sites with and without Faxonius rusticus, with the exception of one macroinvertebrate genus (Ameletus). While there were some significant differences in diversity across macrohabitat types (riffles, runs, and vegetation), overall community structure was not statistically different between treatments. This is best explained by the significant decline in densities of Faxonius rusticus in the Monocacy River since 2016, as higher densities of crayfish would likely lead to more predation. We hypothesize that rates of predation in this system by Faxonius rusticus are not remarkable enough to influence benthic macroinvertebrate community structure as a whole.