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The dual threat affecting reefs around the world—ocean acidification and warming ocean temperatures—is impinging on corals’ ability to build their skeletons. For scientists, the challenge has been to isolate the two effects. Now, researchers at the Woods Hole Oceanographic Institution (WHOI) say they can show the distinct impact on coral growth due to acidifying oceans.

The research work, just published in Geophysical Research Letters, reveals a 13% decline in the density of coral along Australia’s Great Barrier Reef and a 7% decline on two additional reefs in the South China Sea. According to the authors, this density loss is largely attributed to the increase in acidity in the waters surrounding the reefs since 1950.

WHOI scientist Weifu Guo and his co-authors looked at published data collected from the skeletons of Porites corals dating back to 1871, 1901, and 1978, as well as new 3D CT scan images of that genus of coral from reefs in the central Pacific Ocean. This information, combined with historical temperature and seawater chemistry data from each reef, was used in the researchers’ novel numerical model to show that ocean acidification was the cause of the significant decline in skeletal density on the GBR and in the South China Sea.

Although ocean acidification is driven largely by CO₂ emissions, these reefs are additionally impacted by sewage and runoff from land, which causes further reductions of seawater pH.

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