Reading Bones: How Ocean Acidification Affects Coral Reef Health

coral reef
Credit: flickr

Climate change impacts everything around us, from weather to the land, air, and water itself. Due to the rise of carbon dioxide in the atmosphere, ocean acidification levels are rising, which in turn threatens the health and wellbeing of coral reef ecosystems. A study was recently published on how ocean acidification directly affects the health of coral reefs, which are essential for protecting coastlines, providing a habitat for aquatic life, and assisting in the chemical conversions of carbon and nitrogen fixing that are essential for life on earth.

A research team at Woods Hole Oceanographic Institute in Massachusetts published a study on January 28, 2018 that identifies the specific way various coral species is affected by ocean acidification and display the effects of future environment conditions on reefs.  They determined that ocean acidification hinders growth of coral skeleton in the thickening process, which in turn reduces the skeleton’s density and leaves it more vulnerable to breakage.

While it had been theorized that coral calcification rates decline as ocean acidification increases, these predictions hadn’t been consistent in a laboratory setting or when studying corals inhabiting reefs with low pH levels. The WHOI was able to study coral skeletons and determine how pH levels and carbonate ion concentrations effect coral reefs and create a mathematical model that predicts how skeletal density will be effected by climate change and ocean acidification in the 21st century. This research plays an important role in examining the impact we have on the world around us and how human actions will effect ecosystem’s future health.

The team took core skeletal samples of Porites, a common coral, from four locations all over the world where sea water conditions vary in pH level and carbonate ion concentrations. Using a 3-D computerized tomography scanner to image the cores, the researchers found annual growth bands on the skeletons (similar to the growth rings of trees) that imply the skeletons of coral in more acidic environments were significantly thinner.

After developing a numerical model that modeled the growth mechanism of coral skeletons and comparing it to projected changes in ocean acidity caused by climate change, the researchers concluded that declines in coral skeletal density will occur in coral reefs all over the world. The Indo-Pacific region in particular will be greatly impacted; it has been predicted that there will be up to 20% in reductions in skeletal density by 2100. This in turn will affect the overall health of coral and the ecosystems coral provides for a vast array of marine life.

Ocean acidification does not happen in isolation and other environmental effects caused by climate change will inevitably also affect the health of these important ecosystems.


Mollica, N.R., Guo, W., Cohen, A.L., Huang, K.F., Foster, G.L., Donald, H.K., and Solow, A.R. 2018. Ocean acidification affects coral growth by reducing skeletal density. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas. 1712806115 

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