New study suggests coral reefs may be able to adapt to moderate climate change


A new modeling study shows that widespread bleaching events like this one in Thailand in 2010 will become more common in the future. However, the study also found signs corals may be adapting to warming -- the question is if it can be fast enough to keep up with the rate humans are burning fossil fuels. (Credit:C. Mark Eakin/NOAA )

A new modeling study shows that widespread bleaching events like this one in Thailand in 2010 will become more common in the future. However, the study also found signs corals may be adapting to warming — the question is if it can be fast enough to keep up with the rate humans are burning fossil fuels.
(Credit:C. Mark Eakin/NOAA )


Coral reefs may be able to adapt to moderate climate warming, improving their chance of surviving through the end of this century, if there are large reductions in carbon dioxide emissions, according to a study funded by NOAA and conducted by the agency’s scientists and its academic partners. Results further suggest corals have already adapted to part of the warming that has occurred.

“Earlier modeling work suggested that coral reefs would be gone by the middle of this century. Our study shows that if corals can adapt to warming that has occurred over the past 40 to 60 years, some coral reefs may persist through the end of this century,” said study lead author Cheryl Logan, Ph.D., an assistant professor in California State University Monterey Bay’s Division of Science and Environmental Policy. The scientists from the university, and from the University of British Columbia, were NOAA’s partners in the study.

Warm water can contribute to a potentially fatal process known as coral “bleaching,” in which reef-building corals eject algae living inside their tissues. Corals bleach when oceans warm only 1-2°C (2-4°F) above normal summertime temperatures. Because those algae supply the coral with most of its food, prolonged bleaching and associated disease often kills corals.

The study, published online in the journal Global Change Biology, explores a range of possible coral adaptive responses to thermal stress previously identified by the scientific community. It suggests that coral reefs may be more resilient than previously thought due to past studies that did not consider effects of possible adaptation.

The study projected that, through genetic adaptation, the reefs could reduce the currently projected rate of temperature-induced bleaching by 20 to 80 percent of levels expected by the year 2100, if there are large reductions in carbon dioxide emissions.

“The hope this work brings is only achieved if there is significant reduction of human-related  emissions of heat-trapping gases,” said Mark Eakin, Ph.D., who serves as director of the NOAA Coral Reef Watch monitoring program, which tracks bleaching events worldwide. “Adaptation provides no significant slowing in the loss of coral reefs if we continue to increase our rate of fossil fuel use.”

“Not all species will be able to adapt fast enough or to the same extent, so coral communities will look and function differently than they do today,” CalState’s Logan said.

While this paper focuses on ocean warming, many other general threats to coral species have been documented to exist that affect their long-term survival, such as coral disease, acidification, and sedimentation. Other threats to corals are sea-level rise, pollution, storm damage, destructive fishing practices, and direct harvest for ornamental trade.

According to the Status of Coral Reefs of the World: 2000 report, coral reefs have been lost around the world in recent decades with almost 20 percent of reefs lost globally to high temperatures during the 1998-1999 El Niño and La Niña and an 80 percent percent loss of coral cover in the Caribbean was documented in a 2003 Science paper. Both rates of decline have subsequently been documented in numerous other studies as an on-going trend.

Tropical coral reef ecosystems are among the most diverse ecosystems in the world, and provide economic and social stability to many nations in the form of food security, where reef fish provide both food and fishing jobs, and economic revenue from tourism. Mass coral bleaching and reef death has increased around the world over the past three decades, raising questions about the future of coral reef ecosystems.

In the study, researchers used global sea surface temperature output from the NOAA/GFDL Earth System Model-2 for the pre-industrial period though 2100 to project rates of coral bleaching.

Because initial results showed that past temperature increases should have bleached reefs more often than has actually occurred, researchers looked into ways that corals may be able to adapt to warming and delay the bleaching process.

The article calls for further research to test the rate and limit of different adaptive responses for coral species across latitudes and ocean basins to determine if, and how much, corals can actually respond to increasing thermal stress.

In addition to Logan, the other authors of the paper were John Dunne, NOAA Geophysical Fluid Dynamics Laboratory; Eakin, NOAA’s Coral Reef Watch; and Simon Donner, Department of Geography at the University of British Columbia. NOAA’s Coral Reef Conservation Program funded the study.

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Coral Reefs & Climate Change: What the New IPCC Report Says

Bob Lalasz in The Nature Conservancy:


The Intergovernmental Panel on Climate Change has just issued the portion of its Fifth Assessment Report (AR5) that deals with the impacts of climate change on ecosystems and social systems as well as opportunities for adaptation — and coral reefs take center stage in the document. 

The narrative isn’t cheery. Not only does the AR5 call coral reefs a “Unique and Threatened System,” it seems to cast serious doubt on their ability to adapt to a world with atmospheric CO2 levels that now seem almost inevitable. 

Are the prospects that gloomy for coral reefs? No, says Mark Spalding, senior marine scientist at The Nature Conservancy — if policymakers and citizens act in time. I asked Spalding to put the scientific synthesis in the AR5 in context and talk about ongoing and prospective coral reef conservation efforts—especially the Conservancy’s efforts to map ocean wealth and get reef valuation information into the hands of decision makers.


Q: So what’s different in Assessment Report 5 from past ARs about corals and their vulnerability to the effects of climate change? 

Mark Spalding: This report is not the first time the IPCC has singled out coral reefs for attention, and countless other scientists have voiced similar views over the years. The new issues raised in the AR5 come not from any major new science around corals, but rather from a growing concern about the trajectory towards climate chaos and the failure of human society to do anything meaningful to alter those trajectories.

Q: The AR5 calls coral reefs “the most vulnerable marine ecosystem” on Earth, “with little scope for adaptation” to the rising ocean temperatures and increasing ocean acidification now occurring as a result of climate change. Why is that? Aren’t there promising efforts to find out what corals are most adaptable to coral bleaching, for instance?

Mark Spalding: Two reasons for the AR5 statement. First, tropical corals are simple organisms that have adapted to the remarkably stable temperatures of the shallow tropics, and it seems that they are remarkably poorly adapted to even very slight rises in temperature above their local average summer maximum. We’ve seen the impacts of higher temperatures result in “coral bleaching” events across the globe.

Second, like many other organisms, corals have also developed a method for building a skeleton from calcium carbonate, which requires that mineral to be present and accessible in the ocean. But as ocean waters acidify because of rising temperatures, these minerals are increasingly dissolved and inaccessible, resulting in reduced growth rates and strength for coral reefs.

But you’re right — corals are more adaptable than we first thought after the first global mass coral bleaching event in 1998, when many reef scientists were shocked at just how rapidly reefs could be impacted on a global scale.

“Corals do have a limited capacity to adapt. Furthermore, some species appear to be better adapted, both to warming and acidification, than others.” 

Since then, thousands of scientists have pored over this problem and observed the responses of corals in lab experiments and in the field. This knowledge has disproved the most dire predictions about corals’ lack of adaptability. Corals do have a limited capacity to adapt. Furthermore, some species appear to be better adapted, both to warming and acidification, than others.

Q: The AR5 isn’t much more optimistic about the present state of reefs — it says that “the unique systems of the Arctic region and warm water coral reefs are undergoing rapid changes in response to observed warming in ways that are potentially irreversible.” Doesn’t that statement mean that we’re already at impact levels from climate change that are doing permanent damage to coral reefs? 

Mark Spalding: Yes and no. Coral reefs are complex ecosystems, and there’s not a simple on-off switch. Changes will be minor and reversible to begin with, and we’ve seen those pretty much everywhere. Places have suffered mass mortalities, but many have then recovered.

Next comes the changes in balance — weaker corals become rare in the system, and we’ve already seen some of that. But from a bigger perspective, the reefs are still there and functioning pretty much as always. Those changed reefs will continue to offer many of the same services in terms of coastal protection and fisheries and tourism value as the original reefs.

“I’m hopeful that if we can get good management in place, then the next 3-4 decades will see changes rather than wholesale losses to most of the world’s coral reefs.” 

I suspect corals will experience more of these substantive and long-term changes even if we act now to halve greenhouse gas emissions. More catastrophic “tipping points” will come, but even then they will not be simultaneous everywhere, and there is some evidence that we will be able to manage reefs to increase their resilience. It’s the increasing frequency of return events — for instance, if mass bleaching becomes an annual or even biannual event — that might cripple coral reef recovery, growth and reproduction.

Q: Coral reefs aren’t just pretty — more than 500 million people depend on coral reef ecosystems for food and other resources, according to the AR5. But the report also says we have a “relatively poor understanding of the implications” of coral reef decline for the livelihoods of these people. What science do we need to better understand what will happen to these hundreds of millions and how to build better socioeconomic resilience and adaptation? 

Mark Spalding: Big numbers are broad gesturing. They are dramatic and accurate as far as they go, but such numbers are of little use to drive concern and management action.

What we urgently need to understand is the value and value flows of reefs — and the forces that drive changes in these value flows — in sufficient detail, so that we can show exactly how much value any given reef is delivering in terms of jobs, food security, safety or plain dollars).

When we know these numbers, and the complex web of factors that are driving them, then we can also start to model and predict the impacts of threats including climate change, but also the potential benefits from different management approaches. It’s this idea of accurately mapping ocean wealth that will really begin to influence policy and action. The Conservancy has an Mapping Ocean Wealth project designed to capture just this level of accuracy in valuation.

Q: So what’s the best way to reduce stress on corals at this point, given the scenarios the AR5 paints? Should we attack non-climatic stressors like pollution and destructive overfishing practices? The mitigation scenarios are going to have to be amazingly stringent (i.e., achieving CO2 concentrations of 430-480ppm in year 2100) to maintain moderately healthy coral reefs, according to the report.

Mark Spalding: Many reefs have declined dramatically in recent decades due to the host of local pressures that people have created, from overfishing to pollution. For the most part, these pressures remain – and reefs would continue to decline even without climate change. So turning those pressures around is critical, because even in the short-term coral reefs will deliver massive returns on rather low investments in better management.

But more importantly, there is quite a body of evidence that such well-managed reefs may be more resilient and may recover more quickly from impacts such as coral bleaching. I’m hopeful that if we can get good management in place, then the next 3-4 decades will see changes rather than wholesale losses to most of the world’s coral reefs. Efforts such as the Conservancy’s Reef Resilience Network and training for resource managers are leading the way in this space.

In parallel, we do need to start thinking some more wild thoughts. Some scientists have been talking about “assisted colonisation” or moving coral colonies that are better heat adapted to places in their range where they are in decline. The Conservancy and others have begun to grow out vast numbers of coral colonies in nurseries and are transplanting them back to degraded reefs. Such work already involves some level of selection for more robust strains. It remains highly experimental and may not work, but we need to be inventive.

Q: As a scientist, what do you want policymakers to take away from the findings about coral reefs in the AR5? What about citizens?

Mark Spalding: We need to make sure this is converted into a sense of urgency, not a sense of despair. There has been some discussion about whether this report is too gloomy, but the authors are very clear that this latest report is about reporting “risk.” That means describing all probabilities and possibilities.

It’s also easy to get the impression that we are simply buying time. But it is not just about buying time. Coral reef conservation is also about sustaining the millions and millions of people and communities now that depend on reefs for their livelihoods. We can’t possibly give up on coral reefs because of the critical services they provide to people each and every moment of every day of the year.

“Unless we deal with the causes of climate change head-on, this is something much, much bigger than a coral reef problem.”

Coral reefs are not unique in the threats they are under. Along with polar ecosystems, they just appear to be ahead of the curve and are already taking substantial hits from climate change. Other ecosystems, including human agricultural systems, will follow.

The message for policymakers is really to stop talking and stop delaying — act now! Act locally for reefs to safeguard people who depend on them for as long as possible, but also act globally because unless we deal with the causes of climate change head-on, this is something much, much bigger than a coral reef problem.

And the message for the public is the same, but only perhaps to remember that the policymakers serve the public. Public opinion, whether in democracies or not, is a powerful influence on governments.