Ocean acidification is eating away at the skeletons of coral

A new study led by scientists at the Woods Hole Oceanographic Institution (WHOI) has produced detailed evidence of how ocean acidification is threatening the survival of coral reefs. The researchers found that rising acidity in the ocean makes it difficult for corals to build thick skeletons, leaving them more susceptible to deterioration.

“Our research incorporates the nuances of coral skeletal growth, enabling more precise projections of how, where, and by how much, ocean acidification will affect tropical reef-building corals,” said lead author Nathaniel Mollica.

Corals grow their skeletons up toward the sunlight and thicken them for strength. The researchers developed a numerical model simulating this skeletal growth mechanism and paired it with projected changes in ocean acidity.

The study revealed that coral skeletal density will decline across many reefs, with the most prevalent impact in the Indo-Pacific region. By the end of this century, the density of coral skeletons will be reduced by up to 20 percent in parts of the Coral Triangle.

The researchers found that reefs in the Caribbean, Hawaii, and northern Red Sea will experience a reduction in coral density by less than ten percent through 2100.

“This very important study determined the specific way a coral species is affected by ocean acidification and modeled the effect of future environmental conditions,” said co-author David Garrison.

As the ocean acidifies, there are fewer carbonate ions present. This makes it more difficult for corals to make a form of calcium carbonate called aragonite, which is what they use to build up their skeletons.

The corals continue to grow upward, but densification of the skeleton suffers. This means that corals in regions of the ocean with more acidity build thinner skeletons.

The study authors noted that there are other threats to coral growth as well, such as rising ocean temperatures.

“Our next step is to expand our model to incorporate the effects of multiple stressors on corals’ skeletal growth,”said co-author Weifu Guo. “Knowing the details of how the different facets of ocean change will affect corals will enable us to quantitatively project the trajectory of reef-building corals under 21st century climate change.”

The study is published in the Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer