Disease dynamics in freshwater crayfish infected with crayfish plague: lethal and sublethal effects of cuticle lesions, marking methods, and warming temperature on crayfish performance

Abstract

Freshwater ecosystems are increasingly affected by multiple stressors, including emerging diseases and environmental change. Crayfish are important ecosystem engineers that influence sediment structure, nutrient cycling, and aquatic food webs, yet relatively little is known about how disease interacts with environmental stressors and research practices to influence crayfish health and performance. In particular, the effects of crayfish plague and common handling techniques used in ecological studies remain poorly understood. The objective of this thesis was to examine how disease history interacts with research handling and temperature stress to influence survival, growth, molting success, behavior, and lesion development in the crayfish Faxonius virilis. Three laboratory experiments were conducted using crayfish from populations that differed in lesion prevalence history associated with crayfish plague. In the first experiment, crayfish were subjected to two commonly used marking methods, tail punching and visible implant elastomer, to evaluate how handling techniques influenced survival, growth, molting success, and lesion severity. In the second experiment, crayfish were exposed to three temperature treatments to evaluate how thermal stress influenced survival, physiological performance, and lesion dynamics. In the third experiment, an acute thermal ramp assay was used to determine how acclimation temperature influenced thermal tolerance and behavioral responses using a righting response test. Results showed that marking effects were dependent on disease context. Tail punching reduced survival and molting success and was associated with greater lesion severity, particularly in crayfish from the population with higher lesion prevalence, whereas visible implant elastomer marking had minimal measurable effects. Temperature strongly influenced physiological performance, with warmer conditions increasing mortality and altering behavioral responses. Disease history primarily influenced sublethal responses, including lesion development and body condition. These findings demonstrate that disease history can modify the effects of both environmental stress and research practices on crayfish performance. Considering disease context when designing experiments and interpreting ecological responses will improve understanding of how freshwater organisms respond to multiple stressors in changing environments.