3 common coral species could survive climate change better than once believed, scientists say

Coral reefs are known to be extremely vulnerable to the rising global temperatures that are the result of human-caused climate change. According to a new 22-month study, three common coral species in Hawaii may be more resilient to rising ocean temperatures than once thought, and could withstand a temperature increase up to the Paris Agreement tipping point of an average of 3.6 degrees Fahrenheit, NBC News reported.

The new study, “Physiological acclimatization in Hawaiian corals following a 22-month shift in baseline seawater temperature and pH,” conducted by researchers at The Ohio State University, was published in the journal Scientific Reports.

The study simulated ocean temperatures and acidity that are expected to be seen in the future and, while the researchers found that as many as half of some of the species didn’t survive, none of the species disappeared. By the end of the study, some of the corals were even thriving.

Rowan McLachlan, who was the leader of the study as a doctoral student in earth sciences at The Ohio State University, said the results are cause for optimism about the future survival of corals.

“We found surprisingly positive outcomes in our study. We don’t get a lot of that in the coral research field when it comes to the effects of warming oceans,” said McLachlan, who is now doing postdoctoral research at Oregon State University, as reported by Ohio State News.

According to Andréa G. Grottoli, Distinguished Professor of Earth Sciences at The Ohio State University and an author of the study, the findings are more realistic than those of past studies because of the study’s 22-month duration. Grottoli said most comparable research is often conducted over a number of days up to five months.

“There are aspects of coral biology that take a long time to adjust. There can be a dip when they are faced with stressors, but after enough time corals can recalibrate and return to a normal state,” said Grottoli, as Ohio State News reported. “A study that lasts five months is only seeing part of the arc of the response.”

As levels of atmospheric carbon dioxide continue to rise, they cause ocean warming and around 25 percent of the carbon dioxide dissolves into the ocean, causing increased acidity. Both of these factors are dangerous for coral, said Grottoli, as reported by Ohio State News.

During the study, the coral samples of the three most common Hawaiian species (Montipora capitata, Porites compressa and Porites lobata) were exposed to four different ocean conditions. The first had present ocean conditions, the second had acidified ocean conditions, the third warming ocean conditions and the fourth both acidification and warming conditions.

The 40 tanks used in the study were placed next to a reef on Hawaii’s Coconut Island and contained sand, crustaceans, rubble and fish, NBC News reported.

Natural temperature variations and pH levels also occurred in the tanks in order to make them as much like what the corals would have been exposed to in their natural environment as possible, reported Ohio State News.

“When you’re trying to make predictions of the long-term effects of climate change, it is important to mimic the real-world conditions, and our study does that,” said Grottoli, as Ohio State News reported.

The results of the study were that 92 percent of the corals survived in the tanks that simulated present conditions, while 31 percent less survived the warming conditions, Ohio State News reported.

The two Porites species had better survival rates in conditions with increased acidification and warming than the M. capitata species.

The overall survival rates ranged from 46 percent for M. capitata to 71 percent for P. compressa.

“Of the coral that survived, especially the Porites species, they were coping well, even thriving,” said McLachlan, as reported by Ohio State News.

According to Grottoli, M. capitata might have better survival rates in the ocean than they did in the study, as they might have access to more zooplankton, a food source they rely on a great deal when experiencing stress.

Of course, Grottoli said, factors that could negatively affect corals in some places, like overfishing and pollution, were not included in the study.

The Porites species are part of a class of coral seen throughout the world and are important for reef building, and the fact that they did well in the study could be a hopeful sign, said Grottoli.

“We do find something that’s a bit different than other people have found,” Grottoli said, as NBC News reported. “Our conditions were more realistic. Maybe there is more resilience out there. It certainly opens up the window to test that more thoroughly.”