Temporal Transcriptomic Responses of Turbinaria peltata to Repeated Marine Heatwaves and Recovery Cycles

Marine heatwaves (MHWs) are escalating threats to coral reef ecosystems, yet the host transcriptomic mechanisms underlying acclimatization to repeated thermal stress remain poorly understood. Using de novo RNA sequencing, we tracked the temporal transcriptomic responses of the scleractinian coral Turbinaria peltata across two consecutive MHW-recovery cycles. The second heatwave elicited fewer differentially expressed genes (DEGs) than the first (279 vs. 379), whereas the second recovery phase showed the largest DEG set (399). Functionally, the first heatwave triggered acute stress defense and signal suppression, while the first recovery engaged extracellular matrix remodeling and calcium-mediated tissue repair, indicating incomplete restoration. The largest DEG set during the second recovery indicates that recurrent thermal stress imposes cumulative physiological costs demanding more extensive molecular reorganization—spanning metabolic reprogramming, mTOR and Wnt signaling, and sustained oxidative-stress management. Together with prior physiological and microbiome evidence in this species, our results support a model in which repeated heat exposure progressively shifts the coral host from acute shock defense responses toward compensatory metabolism and structural repair. Recovery thus emerges as an active but increasingly costly molecular adjustment under recurrent MHW regimes. These findings identify candidate molecular markers for evaluating coral resilience under intensifying MHW regimes.