A two-year study of coral growth rates in Bermuda, has shown a positive correlation between coral calcification rates and warmer summer ocean temperatures. A new paper based on research led by scientists at Scripps Institution of Oceanography at the University of California San Diego that was published this week in Science Advances.
Coral growth measured in calcification depends on many factors, including temperature, light, food, water flow rates, and competition. In the wild, these factors are further complicated when you include carbonate chemistry, alkalinity, partial pressure of CO2, light, chlorophyll a, and inorganic nutrients.
Scripps chemical oceanographer Andreas Andersson, his graduate student Travis Courtney, and an international team of collaborators from the Bermuda Institute for Ocean Sciences and Christian-Albrecht University in Germany, among others, were involved in the study funded by the National Science Foundation.
The researchers collected temperature, light, and pH readings from two coral reefs in Bermuda over a period of two years. At the same time, they measured the calcification and growth rates of coral samples placed on each of the reefs, as well as seawater chemistry. The team also calculated reef-scale calcification for one of the two reefs studied. All of this information was then analyzed to simplify the relationships between different factors to show which environmental variable affected calcification the most.
“The biggest result was that temperature is the only environmental driver that has significant results for calcification by both coral species at both reef sites and for reef-scale calcification,” Courtney said. “It was the only significant environmental parameter for all calcification measurements that we looked at in this study.”
They found that in Bermuda, coral calcification in two coral Diploria labyrinthiformis and Porites astreoides was relatively insensitive to changes in the seawater pH, but very sensitive to changes in temperature. And the observed relationship between temperature and calcification was a positive one—as the seawater got warmer, coral growth sped up.
While we’re not suggesting you go crank up the heater in your aquarium, this study suggests that wild corals can continue to grow as summer temperature rise. That is until they reach a narrow tipping point when they quickly become stressed, expelling algae and growth rates sharply decline.
The team found that peak summer seawater temperatures of 30°c or 86° F, were not limiting calcification via thermal stress and, instead, that calcification rates are more strongly limited by cooler winter seawater temperatures. [Scripps]