The Potential Roles of Fecundity, Young of the Year Growth, and Young of the Year Mortality on the Displacement of Orconectes virilis by Orconectes rusticus in the Monocacy River, Maryland.

Abstract

The invasive rusty crayfish (Orconectes rusticus) is displacing virile crayfish (Orconectes virilis) in the Monocacy River, Maryland. During 2011 and 2012, I investigated young of the year (YOY) life history traits of both crayfishes to identify displacement mechanisms. I sampled sites dominated by 0. rusticus and 0. virilis and a population interface site. Orconectes virilis was more fecund than 0. rusticus. 0. virilis YOY experienced reduced survival, reduced growth, and smaller year-end size at the overlap site. Orconectes rusticus juveniles show increased growth at the overlap site when compared to 0. rusticus at the dominant site. The 0. virilis YOY population experienced a large loss in YOY by early summer at the overlap site. A decline of 0. virilis YOY was not observed at the 0. virilis dominant site. My results suggest 0. virilis displacement occurs during its YOY stage, and is related to the presence of 0. rusticus.