Climate change is increasing in the frequency and intensity of extreme heat events during European summers. Heat waves are enhancing the water thermal stratification in the Mediterranean Sea with dramatic consequences for coastal ecosystems. As a consequence of these heat waves, it has recently been predicted that Posidonia oceanica meadows could be functionally extinct by the middle of this century. However, there no exist evidences of this cause-effect relationship and almost nothing is known about the tolerance capacity of this seagrass species to warming. There is, therefore, an urgent need to determine the resilience and acclimation capacity of the species for the conservation of these valuable ecosystems, the functions, and the services they provide.The general objective of this research is to find out how sporadic extreme heat events will affect P. oceanica meadows, and to forecast how they will respond under the effects of climate change along the European Mediterranean coasts. To this end, the present project will be based on mesocosm experimentation and will combine novel transcriptomic and ecophysiological approaches for a comparative analysis of plants from contrasting thermal regimes.The main specific objectives are: i) to determine and analyse on an integrated approach the stress responses and tolerance mechanisms of P. oceanica over the course and recovery period of a simulated heat wave, ii) to identify specific genes associated with the tolerance and resilience of the species to heat stress, iii) to compare whether genotypes from thermally contrasting depths of a population differ in their tolerance and resilience to warming, and iv) to compare whether populations from thermally contrasting localities differ in their tolerance and resilience to warming.Findings will represent a substantial and novel contribution to the capacity of the species to adapt to global warming particularly useful to adopt decisions in management and conservation policies