Spatially varying selection between habitats drives physiological shifts and local adaptation in a broadcast spawning coral on a remote atoll in Western Australia

At the Rowley Shoals in Western Australia, the prominent reef flat becomes exposed on low tide and the stagnant water in the shallow atoll lagoons heats up, creating a natural laboratory for characterizing the mechanisms of coral resilience to climate change. To explore these mechanisms in the reef coral Acropora tenuis, we collected samples from lagoon and reef slope habitats and combined whole-genome sequencing, ITS2 metabarcoding, experimental heat stress, and transcriptomics. Despite high gene flow across the atoll, we identified clear shifts in allele frequencies between habitats at relatively small linked genomic islands. Common garden heat stress assays showed corals from the lagoon to be more resistant to bleaching, and RNA sequencing revealed marked differences in baseline levels of gene expression between habitats. Our results provide new insight into the complex mechanisms of coral resilience to climate change and highlight the potential for spatially varying selection across complex coral reef seascapes to drive pronounced ecological divergence in climate-related traits.