Frontiers of Biogeography

This study hindcast the geographic distribution of 18 Indo-Pacific scleractinian coral species, with different sensitivities to modern heat stress, into the last glacial maximum (LGM), some 18,000 years ago, when sea-surface temperatures were 2–4^oC cooler and sea level was ~130 m lower than on contemporary reefs. Identifying geographic provinces from the past may provide clues into genetic affiliations through time and provide some insight into how some coral species might respond to contemporary climate change. Coral habitat in the Indo-Pacific was reduced by 70% in the LGM. We identified five Indo-Pacific biogeographical provinces for corals during the LGM — (i) the western Indian Ocean, (ii) Southeast Asia, (iii) Indonesia and northwestern Australia, (iv) northeastern Australia and the Pacific Islands, and (v) the eastern Pacific. These provinces align with provinces recently identified using genetic markers. Given that the Quaternary was dominated by glacial conditions, the distributional legacies left through glacial dominance over that 2.6 million-year period may have also left evolutionary legacies. These glacial legacies may explain why contemporary corals live close to their upper thermal thresholds, which in turn have major consequences as we move into unprecedented rates of ocean warming.