From the bathtub-warm shallows off the coast of an island in American Samoa, researchers are sounding a rare hopeful note for the future of the world's coral reefs.
As climate change heats the world's oceans, scientists and others who mind the health of the world's coral reefs have watched corals struggle.
Events known as bleaching, when anomalously high ocean temperatures cause corals to lose the colorful algae they depend on for food, have led to colorless coral graveyards in many parts of the world.
"We have had a number of mass bleaching episodes because these warm water events have become more frequent," said Iliana Baums, a molecular ecologist at Pennsylvania State University who studies coral reefs.
Coral reefs, located in ocean environments ranging from the Red Sea to the Caribbean to the Galapagos Islands, are important to ocean life as we know it in many ways. They serve as protective nurseries and feeding grounds for many species of fish and other sea creatures that live in and around them. When they thrive, the corals' sturdy structures can give much-needed protection for islands when tropical storms sweep through.
The puzzle facing researchers, Baums explains, is that corals actually do live in a wide range of ocean temperatures. So in some way, those corals living in hotter ocean waters must either be genetically adapted or environmentally acclimatized to such waters.
Now, a new study published yesterday in the journal Science shows that at least one species of coral is able to adjust to higher ocean temperatures -- a finding that gives some hope for corals in a warmer world.
"It might buy reefs a little more time," said Daniel Barshis, a marine biologist at Old Dominion University who was a co-author on the study.
Barshis and fellow researchers, including lead author Stephen Palumbi of Stanford University, have been working with corals at this site in the National Park of American Samoa for a decade, he said.
Moving corals to a hot zone
In the experiment outlined in the paper, the researchers wanted to see whether corals from one pool whose temperatures rarely reached 90 degrees Fahrenheit were able to acclimate to a pool whose temperatures regularly hit 95 F.
The researchers had found that the corals that grew naturally in the warmer pool were tougher and more resistant to bleaching, and they wondered how much of that was a genetic adaptation versus an acclimatization to environmental factors.
So the researchers took tabletop corals from the relatively cooler pool, transplanted them into the hotter pool and followed them for two years.
"This experiment was trying to see if other corals could become like these very strong corals [in the warmest pool] after a year or two of living in that environment," Barshis said.
To their surprise, the researchers found that the corals from the cooler pool were able to get used to the higher temperatures and in fact became stronger themselves, able to retain their algae and avoid bleaching at higher temperatures.
"So that is an encouraging finding because this would indicate that corals have somewhat of a capacity to, within a generation, deal with higher temperatures," Barshis said.
However, although the transplanted corals improved in their ability to withstand bleaching, they never got quite as good at dealing with high temperatures as the corals that originated in the warmest pool.
How much can they adjust?
This indicates that corals' ability to survive in higher temperatures is probably a combination of genetic adaptation, which takes generations to evolve, and environmental acclimatization.
An analogy might be that of an athlete -- although some people are born faster than others, most runners can improve how fast and long they can run through training, Barshis said. In a way, these corals were able to "train" for higher temperatures.
"Transplanting a coral is like putting them in a training regime. We are training them by exposing them to these extreme conditions," he said.
Mark Eakin, the coordinator of the National Oceanic and Atmospheric Administration's Coral Reef Watch program, has watched coral bleaching events escalate in the Caribbean in recent years and found the study's outcome encouraging.
"It's exciting new work that provides some new hope that certain species of coral can respond more quickly to rising temperatures than we used to believe," Eakin said.
On the other hand, all the scientists interviewed said corals' ability to acclimate has a limit, and the rate of temperature change in the oceans is much faster now than it has been in the past, making it difficult for species and ecosystems to adjust.
Additionally, corals face other threats, such as acidification from climate change, pollution and nutrient runoff, and overfishing -- all of which make them more vulnerable, said Penn State's Baums.
While the research provides evidence that corals may be able to get accustomed to higher ocean temperatures, "this doesn't mean coral reefs are safe from climate change," she said.
Reporter Joshua Learn contributed.
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.
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