Inhabitants of the coral reefs near the submarine springs on the Caribbean Coast of Mexico depend on healthy corals. National Science Foundation-supported researchers are studying how corals respond to ocean acidification at natural undersea springs in an effort to understand and predict ocean acidification and its long-term effects on marine chemistry and ecosystems. [Image 3 of 8 related images. See Image 4.]
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A National Science Foundatoin (NSF)-supported study of corals growing where underwater springs naturally lower the pH of seawater (the lower the pH, the more acidic) found that ocean acidification due to rising carbon dioxide levels reduces the density of coral skeletons, making coral reefs more vulnerable to disruption and erosion. The findings are the first to show that corals are not able to fully acclimate to low pH conditions in nature.
The scientists studied coral reefs along the Caribbean coastline of Mexico's Yucatan Peninsula, where submarine springs lower the pH of the surrounding seawater in a natural setting. The effect is similar to the widespread ocean acidification that's occurring as the oceans absorb increasing amounts of carbon dioxide from the atmosphere.
Led by Elizabeth Crook of the University of California, Santa Cruz (UCSC), the researchers deployed instruments to monitor seawater chemistry around the springs. They also removed skeletal cores from colonies of Porites astreoides, an important Caribbean reef-building coral, and took CT scans of the cores -- done in the lab of Anne Cohen at Woods Hole Oceanographic Institution -- to measure densities and determine annual calcification rates.
The results show that coral calcification rates decrease significantly along a natural gradient in seawater pH. Ocean acidification lowers the concentration of carbonate ions in seawater, making it more difficult for corals to build their calcium carbonate skeletons.
"Carbonate ions are the building blocks corals need to grow skeletons," said Adina Paytan, a marine scientist at UCSC. "When the pH is lower, corals have to use more energy to accumulate these carbonate building blocks internally. As a result, the calcification rate is lower and they lay down less dense skeletons." The reduced density of the coral skeletons makes them more vulnerable to mechanical erosion during storms, to organisms that bore into corals and to parrotfish, which sometimes feed on corals.
The National Science Foundation (NSF) funded this research through its Ocean Acidification Program (grant OCE 10-40952), part of the agency's Science, Engineering and Education for Sustainability Investment.
To read more about this research, see the NSF news release Natural underwater springs show how coral reefs respond to ocean acidification. (Date image taken: 2010-12; date originally posted to NSF Multimedia Gallery: Aug. 25, 2017)