Short-term metabolic stress response of the temperate cup coral Caryophyllia smithii to a simulated marine heatwave

Marine heatwaves (MHWs) are increasing in frequency and intensity due to climate change, posing significant threats to marine biodiversity. While tropical coral responses to thermal stress are well studied, less is known about the responses of temperate, azooxanthellate corals to temperature anomalies. The aim of our study was to investigate the physiological response of the temperate scleractinian coral Caryophyllia smithii to simulated short-term MHW conditions in Irish coastal waters. Using a controlled laboratory experiment, respiration rates were measured in corals exposed to ambient (12.5 °C) and elevated (19 °C) temperatures over a 14-day period. A linear mixed effects model revealed a significant interaction between treatment and time, with corals under elevated temperature exhibiting a pronounced increase in respiration from Day 7 onward, significantly exceeding control values by Day 13. These results indicate a rapid metabolic stress response, suggesting that short periods of elevated temperature consistent with strong MHWs can disrupt physiological homeostasis in C. smithii. Our findings highlight the potential vulnerability of temperate azooxanthellate corals to climate-driven warming and underscore the need to include temperate coral species in climate impact assessments and conservation planning.