Scaling Up: Long-Term, Large-Scale Impacts of the Invasion of Lakes by the Invasive Rusty Crayfish (Orconectes rusticus)

The introduction of nonindigenous species is an increasing threat to global biodiversity and ecosystem function. The success of management efforts often relies on the study of the dynamics and impacts of previous invasions. Small-scale experiments of nonindigenous species provide valuable and timely information, but are limited in their ability to assess adequately the potential long-term effects of invasion at the whole-ecosystem level. Here, I build on previous smaller scale studies of the impacts of the invasive rusty crayfish Orconectes rusticus in order to assess the impacts and dynamics of the invasion at longer temporal scales, larger spatial scales, and more complex levels of ecological organization. Using data from long-term monitoring, I evaluated trends in the crayfish community over three decades in lakes invaded by O. rusticus. Results showed that an earlier congeneric invader, O. propinquus is extirpated, while the native O. virilis tends to coexist by using a habitat refuge. Patterns of O. rusticus abundance were more variable than previously believed. Most lakes sustained high O. rusticus abundance through time, while a few exhibited a pattern of boom-and-bust. Long-term O. rusticus abundance appeared to be related to risk of fish predation, variation in lake benthic substrate, and crayfish resource limitation. A long-term, whole-lake survey of snail and crayfish abundance showed that the magnitude of impact by O. rusticus can be great, differs across habitats, and that the full extent of impact on congeners and prey may not be evident until many years after initial colonization. Analysis of snail gut contents and a set of laboratory feeding experiments demonstrate that snails do not consume macrophytes, indicating that the primary effect of O. rusticus predation on snails is reduced grazing efficiency on periphyton. Samples from two lakes that experienced large declines in O. rusticus abundance indicated little ecosystem recovery. Comparison of food webs in invaded and uninvaded lakes using stable isotopes provided evidence that O. rusticus decoupled littoral and pelagic food webs. The combined effect of reduced grazing efficiency and food web decoupling is likely to be reduced flow of energy to the top of the lake food web.