Data for "Acute heat tolerance (CTmax) of two invasive parasitic copepods differs across life cycle stages, species and acclimation temperature"

1) Climate change is increasing the frequency and severity of heatwaves with potential consequences for host–parasite dynamics. While the acute heat tolerance of free-living organisms has been intensively studied, much less is known about it for parasites and their life cycle stages. 2) We investigated critical thermal maxima (CTmax) in two closely related marine invasive parasitic copepods (Mytilicola orientalis and M. intestinalis) that infect bivalves in the European Wadden Sea, using temperature ramping assays across life cycle stages (free-living larvae and parasitic adult females) that mimicked rapid warming periods during heatwaves occurring in the spring and summer. 3) CTmax values of both life cycle stages of the two parasite species were relatively high (36-46 °C), considering local environmental temperatures and typical CTmax values of free-living copepods. The values differed by species and life cycle stage with ontogenic differences partially depending on the acclimation temperature (spring 14 °C or summer 20 °C). Overall, M. orientalis exhibited significantly higher CTmax than M. intestinalis, both for the adult and the larval stages (6.6-6.8 °C and 3.9-4.2 °C higher, respectively) at both acclimation temperatures. Within M. orientalis, larvae had 2.6-4.8 °C lower CTmax than adults at both acclimation temperatures, while M. intestinalis showed a stage-specific variation of 2.2 °C only when acclimated to 14 °C. Larval stages of both species had 2.8-3.1 °C higher CTmax values when acclimated to 20 °C compared to 14 °C, whereas no effect of acclimation temperature was seen among adults of either species. 4) Our results suggest that parasitic copepods have a high acute heat tolerance that depends on the species, life cycle stage and seasonal temperature acclimation, with implications for heatwave tolerance. While current summer heatwaves do not exceed the CTmax of parasites acclimated to summer temperatures, the lower CTmax values when acclimated to spring temperatures may indicate negative effects of spring heatwaves on larval stages. Beyond our study, the CTmax approach may be a practical tool to investigate the acute heat tolerance of parasites.