Van Loon1 argues that, just because coral reefs survived the geological past, global change is not a threat to them. It surely depends on the time-scale over which such change occurs. Corals survived sea-level fluctuations, in particular rapid drowning at the last glacial termination, but there are indications that reefs took 1,000 years to become re-established on the new shelves10.
Today's reef bleaching can be compared to what happened at the Cretaceous/Tertiary boundary, when carbon dioxide and temperature levels rose shortly after the asteroid impact. Spectacular shell abnormalities are present in reef foraminifers today11, and similar effects occurred just after the boundary12. Reefs took about 10 million years to recover, mainly by recolonization by small corals or deep-sea forms13.
Reef decay will probably not be so great in the future, but the geological record gives a taste of what may be to come.
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