The impact of climate change on the earth’s oceans has been studied extensively over the past two decades. With an increasing amount of evidence detailing it’s negative effects on the marine environment, scientists are striving to identify ways to repair the damage that has already been done and to find solutions to prevent future damage. One of the primary impacts of climate change on our oceans, ocean acidification, is an emerging global problem that is attributed to the uptake of atmospheric carbon dioxide by our oceans.

In a new study, University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science researchers found that the limestone that forms the foundation of coral reefs along the Florida Reef Tract is dissolving during the fall and winter months on many reefs in the Florida Keys, which they attribute to ocean acidification.

Each year the oceans absorb CO2 from the atmosphere and become more acidic. The rapid uptake of heat energy and CO2 by the ocean results in a series of changes in seawater carbonate chemistry, including reductions in pH and it’s carbonate saturation state. Currently surface waters are supersaturated with respect to all forms of calcium carbonate, however with increasing ocean acidification, ocean pH falls and reduces the carbonate ion concentration, making the calcium carbonate structures of many marine organisms vulnerable to dissolution.

Limestone, which forms the foundation of coral reefs is primarily composed of calcium carbonate, hence an increase in ocean acidity is resulting in the dissolution of these reef structures. During the spring and summer months in the Florida Keys, environmental conditions in the ocean such as water temperature, light and seagrass growth, are favorable for the growth of coral limestone. While, during the fall and winter, low light and temperature conditions along with the annual decomposition of seagrass, result in a slowing, or small-scale loss of reef growth. However, as atmospheric CO2 is absorbed by seawater, ocean pH declines. The result is that the natural summer growth cycle of coral is no longer large enough to offset the effects of dissolution from ocean acidification.

The extensive thickets of staghorn corals are gone today, replaced by a structure-less bottom littered with the decaying skeletons of staghorn coral – Photo credit: Chris Langdon Ph.D

For two years, the team of researchers collected water samples along the 200-kilometer (124-mile) stretch of the Florida Reef Tract north of Biscayne National Park to the Looe Key National Marine Sanctuary. The results showed that reef dissolution is a significant problem on reefs in the upper Keys with the loss of limestone exceeding the amount the corals are able to produce on an annual basis. As a result these reefs are expected to begin wasting away leaving less habitat for commercial and recreationally important fish species. Florida Keys’ reefs have an estimated asset value of $7.6 billion.

“We don’t have as much time as we previously thought,” said Chris Langdon, UM Rosenstiel School professor of marine biology and ecology, and a senior author of the study. “The reefs are beginning to dissolve away.” “This is one more reason why we need to get serious about reducing carbon dioxide emission sooner rather than later,” said Langdon.

JK

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