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A healthy coral reef with both hard corals and softer-bodied relatives at Chinchorro Reef in the Mexican Caribbean Sea. Credit: David Paz-Garcia

World - Warmer, acidifying ocean brings extinction for reef-building corals, renewal for relatives

Changes in ocean chemistry and temperature have had a dramatic effect on the diversity of corals and sea anemones, according to a team of scientists who have traced their evolution through deep time.

A new study, published Aug. 31 in the journal Nature Ecology and Evolution, finds that reef-building corals emerged only when ocean conditions supported the construction of these creatures' stony skeletons, whereas diverse softer corals and sea anemones flourished at other times. Without a significant change to anthropogenic carbon emissions, the new findings present stark implications for the present and future of hard-bodied corals while suggesting a silver lining for the diversity of some of their softer-bodied relatives.

New genetic analyses show that corals, which together with sea anemones make up a class of animals known as anthozoans, have been on the planet for 770 million years. That is 250 million years before the earliest undisputed fossil evidence of their existence—and long enough to experience massive shifts in climate, fluctuations in ocean chemistry and several mass extinctions.

In the new study, a research team led by scientists from Harvey Mudd College, the American Museum of Natural History and the Smithsonian's National Museum of Natural History examined how these past conditions affected anthozoan diversity. That was possible thanks to a new molecular approach developed by Andrea Quattrini, research zoologist and curator of corals at the National Museum of Natural History, Catherine McFadden, a biologist at Harvey Mudd College, and Estefanía Rodríguez, a curator at the American Museum of Natural History, which allowed the team to compare nearly 2,000 key regions of anthozoan genomes to discern the evolutionary relationships between species. The team analyzed hundreds of anthozoan specimens that were collected from around the world and are now stored in museum collections. When this molecular data was aligned with fossil evidence of anthozoan history, it revealed how these diverse animals evolved over geologic time.

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