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Yucatan study shows how resilient the coral reef really is

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Coral, like this off the coast of Cozumel, could suffer from skeleton density issues. Photo: Getty

A study led by scientists at UC Santa Cruz shows that at least three Caribbean coral species, off the Yucatan Peninsula, can survive and grow under an increasingly acidic ocean, but the density of their skeletons may be lower than normal.

The study took advantage of the unusual seawater chemistry found naturally at sites along the Mexico’s Caribbean coastline, where water discharging from submarine springs has lower pH than the surrounding seawater.

In a two-year field experiment, the international team of researchers transplanted genetically identical fragments of three species of corals to a site affected by the springs and to a nearby control site not influenced by the springs. Then they monitored the transplants. They reported their findings June 26 in Proceedings of the Royal Society B.

“The good news is the corals can survive and deposit calcium carbonate, but the density of their skeletons is reduced, which means the framework of the reef would be less robust and might be more susceptible to storm damage and bioerosion,” said a study co-author, Adina Paytan, a research professor at UCSC’s Institute of Marine Sciences.

Of the three species tested, the one that performed best in the low-pH conditions was Siderastrea siderea, commonly known as massive starlet coral, a slow-growing species that forms large dome-shaped structures. Another slow-growing dome-shaped species, Porites astreoides (mustard hill coral), did almost as well, although its survival rate was 20 percent lower. Both of these species outperformed the fast-growing branching coral Porites porites (finger coral).

Co-author Donald Potts, professor of ecology and evolutionary biology at UC Santa Cruz, said the transplanted species are all widespread throughout the Caribbean.

“The slow-growing, dome-shaped corals tend to be more tolerant of extreme conditions, and they are important in building up the permanent structure of the reef,” he said. “We found that they have the potential for persistence in acidified conditions.”

Corals will have to cope with more than ocean acidification, with climate change resulting in warmer ocean temperatures and rising sea levels. Unusually warm temperatures can disrupt the symbiosis between coral polyps and the algae that live in them, leading to coral bleaching. And rapidly rising sea levels could leave slow-growing corals at depths where they would die from insufficient sunlight.

Nevertheless, Potts noted that several species of Caribbean corals have long fossil records showing that they have persisted through major changes in Earth’s history.

“These are species with a history of survival and tolerance,” he said.

Source: Press release

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