Species-specific seasonal variations in thermal performance curves shape the direct and transgenerational vulnerability to marine heatwaves

Research Highlights: Sasaki, M., Finiguerra, M. & Dam, H.G. (2024). Seasonally variable thermal performance curves prevent adverse effects of heatwaves. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.14221. Marine heatwaves (MHWs) emerge as a devastating stressor that can have direct and transgenerational effects on marine organisms. However, we know very little about how seasonal variations in thermal performance curves (TPCs) may help marine zooplankton cope with these direct and transgenerational effects of MHWs. In a recent study, Sasaki et al. (2024) combined field observations and simulated laboratory heatwave experiments, uncovering seasonal variations in TPCs for key fitness-related traits, including egg and offspring production, hatching success and survivorship in two ecologically important copepod species Acartia tonsa and A. hudsonica. They discovered that the TPC of A. tonsa was highly seasonally variable, allowing them to maintain their thermal optimum of at least 5°C above the field temperature. The transgenerational effects of parental exposure to MHWs on the offspring were minor. In contrast, the TPC of A. hudsonica was relatively unchanged across seasons, suggesting that this species may be highly vulnerable to MHWs, especially during summer. These findings agree with distinct seasonal abundances of the two species in nature: A. hudsonica is primarily abundant during winter and spring while A. tonsa dominates the summer and fall. These findings enhance our understanding of how seasonal variations in TPCs can determine the vulnerability of marine species to heatwaves through direct and transgenerational effects, which are important for ecological risk assessments of marine ecosystems under a rapidly changing climate.