The Invasive Spread of the Rusty Crayfish Faxonius rusticus and Its Impacts on the Established Virile Crayfish Faxonius virilis in the Monocacy River

Abstract

The rusty crayfish (Faxonius rusticus) has invaded lakes and rivers across North America, displacing resident crayfish species in the process. Faxonius rusticus has been moving down the Monocacy River since at least 2007 displacing the established population of the virile crayfish (Faxonius virilis). We quantified changes in the species composition of the crayfish community, size distribution and habitat preferences of crayfish over the length of the Monocacy River in Maryland. Invaded sites experienced an initial increase in F. rusticus (> 90% of crayfish) followed by a decrease approximately 5 years post-invasion (40-60 %). F. virilis numbers were greatly reduced during the initial invasion period but the population likely persisted due to a size refuge, with a small proportion of F. virilis exceeding the maximum size of F. rusticus. Faxonius rusticus’ generalist habitat preferences may allow it to invade more easily to outcompete F. virilis by establishing itself in vacant habitats.