Evaluating Predicted Coral Heat Stress Phenotypes and Microbial Associations in Nursery- Propagated Corals During a Real-World Bleaching Event

<title>Abstract</title> <p>Developing methods to quickly and effectively identify and propagate thermotolerant corals will likely be a key component of coral reef management under future climate scenarios. While heat stress assays have been used to predict coral thermotolerance for nursery propagation, how predictions reflect real-world performance after propagation in nurseroies across different environments and relate to underlying coral microbiology remains unclear. Consequently, we quantified the thermotolerance and associated microbial communities of 54 genotypes of three coral species (Acropora millepora, Pocillopora damicornis and Acropora loripes) from three sites on the Northern Great Barrier Reef (GBR) using acute heat stress assays via the Multi-Taxa Phenotyping (MTP) system. Corals were propagated in coral nurseries at two sites, and their respective bleaching responses were quantified relative to T0 through the 2024 global mass coral bleaching event. We evaluated the relationship between MTP derived Effective Dose 50 (ED50), quantitative changes in coral colour, symbiont and bacterial communities and environment. Our results indicated critical context dependency of bleaching responses in relation to environment and coral species in line with predicted thermotolerance but independent of microbial associations. Consequently, we suggest that future thermotolerance screening must consider spatial variability in environmental conditions and potential influences of environment on phenotype.</p>