Rapid heat stress assays predict survivors of coral bleaching

Quantifying heat tolerance within and among coral species is essential for understanding adaptive capacity and informing restoration programs. Acute heat stress assays are increasingly used to generate high-throughput heat tolerance data for reef-building corals worldwide. However, the ecological relevance of metrics obtained from these assays is still poorly understood. Here, we examine six heat tolerance metrics assessed in over 550 individuals within three Acropora species, relating metrics to in-situ bleaching and mortality following a marine heatwave event, and assessing their temporal consistency. Chlorophyll retention (NDVI) provided the most consistent values with the best predictions of future mortality, where the top 5% of individuals were 25% more likely to survive a heatwave compared to individuals at the median metric value. We demonstrate the utility of measuring multiple metrics when undertaking acute heat stress assays in corals, especially if metric values will be used as a proxy for bleaching resistance or survival under future warming conditions.