Assisted adaptation of kelps for a warmer ocean: Thermal priming and induction of memory stress in Macrocystis pyrifera and Eisenia arborea

Kelp forests are under increasing threat from ocean warming and marine heatwaves. In this context, assisted adaptation techniques emerge as promising tools for optimizing conservation and restoration strategies. One such technique is the cross-generational induction of stress memory by thermal priming, which aims to stimulate the thermal tolerance of kelps in the face of warming. However, research into these processes is still in its infancy. Here, we evaluated whether sublethal warming (priming) applied to gametophytes (23 °C for 21 days) enhances the thermotolerance of the resulting juvenile sporophytes of Macrocystis pyrifera and Eisenia arborea . After the priming phase, we compared the biological performance of juvenile sporophytes derived from primed and non-primed gametophytes at two temperatures: a severe warming (25 °C for five days) that simulates regional marine heatwave conditions, and a control temperature of 17 °C. Under severe warming, sporophytes derived from non-primed gametophytes experienced complete mortality in both species, whereas sporophytes derived from primed gametophytes survived, maintained physiological function and grew. These sporophytes exhibited similar or even higher photosynthetic capacities than those at 17 °C and did not show evidence of oxidative damage. Overall, these findings indicated that applying thermal priming to gametophyte stage can increase thermotolerance in subsequent juvenile sporophyte generations, preventing mortality and improving physiological performance at temperatures that would otherwise be lethal. The present study provides initial evidence that thermal priming can induce cross-generational stress memory in M. pyrifera and E. arborea . These findings support further investigation of thermal priming as a potential assisted-adaptation strategy for kelp conservation, restoration, and cultivation.