Minor Coral Diversity Loss but Long‐Lasting Coral Reef Crises in the Early Paleogene Hothouse

The future of tropical coral reefs is severely threatened by rising global temperatures and relies on the persistence of two key attributes: (a) coral biodiversity, and (b) the reef-building capacity. In order to understand how these attributes responded to a climate warming, we investigated corals and coral reefs in the early Paleogene “hothouse” interval. We focused on the Mediterranean region, which was the global center of reef coral diversity and provides the most complete record for this time interval. We computed biodiversity dynamics of reef corals based on a new compilation of Paleocene to Eocene reef coral occurrences and compared these with coral reef development recorded in the PaleoReefs Database. Extinctions and diversity were within background fluctuations across the Paleocene-Eocene Thermal Maximum (PETM). Coral diversity increased rapidly in the aftermath of the PETM and remained high across the entire Eocene. But reef building collapsed at the PETM and recovered to late Paleocene levels only by the late Eocene. We document that reef corals have demonstrated an excellent resilience within the hothouse, whereas coral reefs were much more vulnerable and took much longer to recover. Our findings suggest that although coral reefs might disappear in the near future, corals will persist and could begin reconstructing reefs once environmental conditions allow.