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The Next Extinction May Be On the Way — But Stony Corals Could Survive

Sixty-six million years ago, when the most recent major extinction killed off 80% of animal species, stony corals survived. They made it through thanks to evolutionary adaptations like living in smaller colonies or living alone, growing more slowly, and living deeper in the ocean.

According to a new study in Scientific Reports, some stony corals today share these same “survival traits” and could be poised to survive the next major extinction, which some scientists say has already begun. Professor David Gruber (Baruch College, The Graduate Center), was an author on the study.

These findings, the authors say, shine an uncomfortable light on the fact that we Homo sapiens have not evolved to have such survival adaptations. As temperatures rise, habitats fragment, oceans acidify, and extinction rates begin to match previous wipeouts, creatures like coral that can adapt are definitely at an advantage.

The researchers looked through the fossil record and examined data from the International Union for Conservation of Nature’s Red List of Threatened Species, which rates extinction risk from “critically endangered” to “least concern.”  The data allowed them to see how stony coral traits have changed throughout history. The corals that survived the end-Cretaceous extinction, they found, were those that lived in small groups or as lone polyps rather than big reef colonies. They also lived at least 100 meters below sea-level, were bleaching-resistant, and didn’t have the same relationship with algae as their surface-dwelling relatives.

Eventually these trends reversed and coral reefs re-established after 2 million to 5 million years. But recently, the study says, there have been changes that look very similar to those of the last extinction. In other words, corals are now showing the same “dynamic survival response” that they did the last time much of Earth’s fauna and flora was going extinct, the paper says.

On one hand, the results suggest that stony corals — the slower-growing ones in deeper waters — could survive the current Anthropocene extinction. But the changes will mean less reef-building in the short-term, which will affect the tens of thousands of species that coral reefs support.