Food web consequences of long-term invasive crayfish control

Abstract

Controlling invasive species can restore ecosystems while also quantifying species interaction strengths. We experimentally removed invasive rusty crayfish (Orconectes rusticus) from a Wisconsin lake. Rusty crayfish abundance declined by 99% in 8 years and did not significantly increase 4 years postharvest, with no compensatory recruitment response observed. Native crayfish (Orconectes virilis) and sunfish (Lepomis spp.) abundances increased by two orders of magnitude as rusty crayfish abundance declined, and macrophyte cover increased significantly in 2–4 m waters. We expected benthic macroinvertebrate densities to increase as rusty crayfish were removed; however, fish consumption of invertebrates increased as rusty crayfish density declined, and macroinvertebrate responses varied among families and habitats. Total Gastropoda density increased 300-fold in cobble, while the density of one gastropod family declined in macrophytes. Ephemeroptera, Odonata, and Amphipoda densities also declined in certain habitats as rusty crayfish were removed, suggesting that they are indirectly facilitated by rusty crayfish. This study highlights the importance of considering indirect effects when assessing the impacts of invasive species and demonstrates that these impacts may be reversed over relatively short time scales.