Ocean Acidification Threatens Economies And Marine Life

Evidence for ocean acidification abounds, but what that means for different organisms has been hard to pin down. A recent study finds that at least one coral species won’t be able to acclimatize to more acidic waters (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1301589110).

Led by Elizabeth D. Crook of the University of California, Santa Cruz, researchers sampled Porites astreoides corals from waters in the Yucatan Peninsula with a natural pH gradient.

The researchers used computed tomography (CT) scans to determine annual growth rates over four years and skeletal erosion due to wear-and-tear or predation. Then they assessed how these measures vary with the water’s carbonate ion concentration, which roughly tracks pH.

Some of the corals came from waters with a pH just above 8.0, which is near the average value for oceans. Others came from an area with much less carbonate than average, where pH is 7.2–7.6. They found that corals in low-carbonate waters calcified 30% less, their skeletons were 28% less dense, and their bioerosion was nearly twice as extensive. These effects worsened in areas with even more acidic waters. The observed trends mirror those seen in short-term lab studies, suggesting they would persist over a lifetime, Crook says.

Chris Langdon of the University of Miami is concerned by the study’s findings. He notes that the oceans are becoming warmer, which also negatively affects coral. Research on how these two factors synergize is a growing field, he adds. Study coauthor Adina Paytan of UC Santa Cruz says that coral reefs serve as frameworks for diverse ecosystems and help humans by providing tourism opportunities, coastal protection, and homes for seafood.

Adding to the gloom, a new United Nations report says human activities that generate carbon emissions are acidifying the oceans and the problem could get far worse without emission cuts. By 2050, ocean pH could drop to 7.8 on average, a 150% acidity increase over preindustrial values of around 8.2. The economic impact of these changes could reach billions of dollars, the report warns.