Thermal priming mitigates the effects of lethal marine heatwaves on the Manila clam Ruditapes philippinarum

Climate extreme events like heatwaves (HWs) increasingly threaten marine ecosystems. Using the Manila clam <i>Ruditapes philippinarum</i> as a model organism, this study assessed the effects and costs of thermal priming in a realistic scenario. Results showed increased resilience to lethal HWs in primed clams, with significantly higher survival and better defensive behavior compared to naÏve clams. Priming costs were evidenced by a reduced condition index, but hardened animals showed higher antioxidant capacity, upregulation of heat shock response genes, and shifts in microbial composition favoring beneficial taxa. Gene expression analysis revealed environmental memory via upregulation of respiratory chain complex genes, detectable 38 days after priming-the longest reported in molluscs in a controlled setting. Evidence suggests that thermal priming can be an effective mitigation strategy not just for Manila clams but, potentially, for other farmed shellfish species (e.g., oysters and mussels) and for ecological conservation projects against climate extreme events.