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The global carbonate production of reefs is applied as a measure of the health of the reef ecosystem in a given time interval. Hence global reef crises are defined as significant drops in the global reefal carbonate production. This definition differs from the measure of diversity to detect evolutionary crises and mass extinctions, and it has two major implications: (1) Reef crises may be linked to mass extinctions defined by global biodiversity decreases, but are not necessarily so. (2) Reef crises can take place during very short time intervals Linked to catastrophic events, but they can also extend over prolonged periods of time.

Our PaleoReefs database was used to calculate reefal carbonate production on a stage level and to quantify Phanerozoic reef crises. We determined eight first-order reef crises (carbonate production loss > 90%) (in decreasing order of magnitude) at the Triassic-Jurassic, Permian-Triassic, end-Ordovician, Pliensbachian-Toarcian, Mississippian-Pennsylvanian, Frasnian-Famennian, Berriasian-Valangin-ian, and Artinskian-Kungurian boundaries. Second-order reef crises (loss 75-90%) were seen at the Middle-Late Permian, Cenomanian-Turonian, and Valanginian-Hauterivian boundaries.

The magnitudes of reef crises and global marine diversity losses may differ substantially. As evidenced for the Cretaceous-Tertiary boundary, synecological patterns in reefs are not necessarily interrupted by mass extinction events. Although many reef crises coincide with major mass extinction events, some crises are associated with only minor extinctions or even with evolutionary radiations (Middle Ordovician, Early Permian). Reef crises affect all reef builders, including corals, sponges, and bivalves. Even microbes are not necessarily disaster forms that survive reef crises. The paleogeographic reef distribution pattern is nearly always constricted during major reef crises. The most commonly observed pattern is a latitudinal narrowing and northward shift of the reef zone. The geographic range of reefs prior to the crisis had no influence on the magnitude of the crisis.

Applying the criteria for reef crisis to reef recovery, we define reef recovery as the time when a first significant increase in the global reef carbonate production becomes evident. Reef recovery usually takes a substantially longer time than the recovery of global biodiversity and is in the range of 5–30 million years. Recovery time is nearly independent of crisis intensity in the reef ecosystem.

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