Response of Acropora to warm climates; lessons from the geological past

There is currently widespread concern about the deterioration of living reef corals, such as Acropora, and tropical reefs. Much of their demise appears to be related to coral bleaching, the underlying cause is probably global climatic warming. Future predictions about the responses of modern coral reefs lacks data from the geological past. The fossil record shows reef coral distributions are highly sensitive to climatic change, modulated by the availability of habitat. Here we follow the history of one individual taxon, Acropora, to demonstrate how a particularly important reef coral genus has responded to global change through its geological time-span. Acropora is the most diverse, widespread and abundant of today’s tropical reef corals, with its centre of diversity in the Indo-West Pacific. Counterintuitively, it was previously absent from this region but was
common in the Paleogene to early Neogene in Europe, including high palaeolatitude (48˚N) Eocene occurrences of southern England and northern France. We have assessed a unique set of unaltered, but fragmented, specimens of Acropora from the Eocene of the Paris and Hampshire basins for their preservational state, diagenesis, and stable isotopic composition (δ18O and δ13C). Results suggest post-mortem parautochthonous to autochthonous deposition in low-energy embayments, with rapid burial in silty muds creating a relatively enclosed geochemical system. Taxonomic uniformitarianism and stable isotope data confirm that Acropora existed in tropical-like climatic conditions in Northwest Europe during the Eocene.