Habitat, predation, and coexistence between invasive and native crayfishes: prioritizing lakes for invasion prevention

No detectable changes in crayfish behavior due to sublethal dietary mercury exposure

Mercury, and particularly its organic form, methylmercury (MeHg), is a ubiquitous environmental contaminant with documented dosage-dependent adverse effects on endpoints spanning many levels of biological organization. However, relatively little is known about the sublethal impacts of environmentally-relevant exposures on behavioral characteristics that may impact predator-prey relationships, and thus the potential for Hg bioaccumulation within food webs due to behavioral impairments. This study investigated the potential for dietary mercury exposure to impair two behavioral outcomes in the highly invasive rusty crayfish, Faxonius rusticus, which are expected to influence interactions with their fish predators: the tail-flip escape response and chelae pinch strength. Field-caught animals were randomly assigned to four dietary treatments with mean (±1 SE) dry-weight total Hg (THg) concentrations of 3.52 ± 0.57, 114.01 ± 4.05, 274.10 ± 0.38, and 565.79 ± 1.33 ng/g in the control, low, moderate and high exposure treatments, respectively, for 16 weeks. After initial observations, exposures began and mass and behavior were measured every two weeks. At the end of the experiment, THg concentrations in tail muscle tissue were significantly higher in the high exposure treatment than in the control and low exposure treatments (Tukey's HSD, family-wise α = 0.05). Exposure-dependent declines in survival, mass, pinch strength, or tail-flip escape response velocity were not detected within the 12- to 16-week experimental exposure period, which represents one season of the crayfish's 3-4 year lifespan. This suggests that crayfish may be relatively tolerant of dietary exposure to sublethal concentrations of mercury within a single season. Further investigation of the physiological underpinnings of this tolerance is warranted.

Habitat explains patterns of population decline for an invasive crayfish

Invasive nonindigenous species are defined by their impacts: they substantially change native communities or ecosystems. Accordingly, invasive species might transform their habitats in ways that eventually become unfavorable to them, causing population declines or even extirpations. Here we use over 40 yr of systematically collected data on the abundance of the invasive rusty crayfish Faxonius rusticus from 17 lakes in northern Wisconsin, USA to explore whether population declines of this invader are related to the prevalence of rocky habitat, which shelters crayfish from predators and is unchanged by crayfish. We predicted that lakes with rock-dominated substrates would be resistant to F. rusticus population declines, whereas lakes lacking rock-dominated substrates would experience F. rusticus declines due to crayfish destruction of shelter-providing macrophytes. We found that in nearly one-half (47%) of the study lakes, F. rusticus experienced population declines over the study time period, and these lakes had significantly lower proportions of rock substrate than lakes that did not experience population declines. We recommend that more studies should investigate the potential for invasive species-mediated community or ecosystem feedbacks to eventually contribute to their own population declines.