Combined-stress priming alters physiology, transcriptional dynamics, and acute thermal resistance in Acropora cervicornis corals

Enhanced resilience conferred through sublethal stress pre-exposure may be crucial for reef building corals to cope with variable environments. The effect of stress priming on Acropora cervicornis thermotolerance was evaluated in the context of elevated temperature and ammonium enrichment, 3 and/or 6 M above ambient, respectively. Primed corals were pre-exposed to each stressor individually or in combination for eight days, while non-primed corals remained at ambient conditions. After an eight-day recovery, primed corals and a subset of non-primed corals (naive) were subjected to an acute 15-hour thermal challenge. Coral metabolism, symbiosis, and gene expression were characterized throughout the experiment. Thermal tolerance was quantified as algal symbiont, chlorophyll, and live tissue retention, along with survival probability following acute heating. Primed corals were more likely to retain symbionts and chlorophyll after heat stress and also exhibited slower tissue loss. Moreover, thermal pre-exposure reduced the risk of tissue loss or predicted mortality. Apoptotic regulation differed between primed and naive corals during the initial and secondary heat exposures. Additionally, primed corals exhibited patterns of transcriptional resilience under acute thermal stress. Altogether, results provide support for the capacity of A. cervicornis to gain resilience through pre-exposure to ecologically relevant conditions as well as insights into the molecular mechanisms underpinning this process.