The Neothetyan circum-Mediterannean record as a suitable archive to understand the response of reef corals to the warming events of the Early Paleogene

Providing empirical evidence about the response of tropical shallow-water organisms to past warming and hyperthermal events is particularly important considering that they are severely threatened by current global warming. Stratigraphic resolution in shallow-water sections cannot be as precise as in pelagic environments and the empirical evidence is usually limited to a “before-and-after” comparison to assess the biological effects of events.

During the early Paleogene, the Neothetyan circum-Mediterranean region was the global center of reef coral diversity. Our compilation of Paleocene to Eocene reef coral occurrences allows for an analysis of reef coral responses to the major climatic changes of this time interval in unprecedented temporal detail, including the Paleocene-Eocene Thermal Maximum (PETM), when global mean temperatures reached more than 5°C above pre-industrial levels.

Reef corals were negatively affected by the PETM as we document a small decrease in diversity at both species and genus level and an increase of extinction rate across the hyperthermal event. During the onset of the Early Eocene Climate Optimum (EECO), diversity gradually increased as also documented by a peak of origination rate. The EECO diversity high is mainly related to the rich coral fauna recently described from NE Italy where the EECO and post-EECO phases are characterized by an accurate specimen-based systematic revision of museum collections associated to a detailed biostratigraphic calibration.

The Late Eocene cooling was accompanied by an increase in diversity, with the origination of several Oligocene coral taxa and the extinction of Eocene ones. The Late Eocene is also the time when coral reefs started to flourish again after the crisis of Late Paleocene-Early Eocene.

 

^{This study was funded by the Italian Ministry of Education and Research (MIUR), funds PRIN 2017: project “Biota resilience to global change: biomineralization of planktic and benthic calcifiers in the past, present and future” (prot. 2017RX9XXY).}