As the climate warms up, ocean heat waves are damaging coral – causing what’s known as coral bleaching. Scientists have established this fact and detailed the present and future consequences. Now, it’s time to do something about it. This is the basic motivation behind a National Academies of Sciences, Engineering, and Medicine study conducted by a committee chaired by Stanford University marine biologist, Stephen Palumbi. The first of these reports was published Nov. 28 and the second report is scheduled to come out in 2019.

Damselfish swimming around coral in a Palau

Damselfish swim around coral in Palau. (Image credit: Rob Dunbar)

“This is the first of two reports which are intended to determine what we can do to make coral reefs more resilient to climate change,” said Palumbi, who is the Jane and Marshall Steel Jr. Professor in Marine Sciences and a professor of biology in the School of Humanities and Sciences. “This report is like laying out your tools to see what people are talking about, what they have tested already, how far they’ve gotten, what the risks are, the limits, the advantages, the costs. Everything that we could find out about interventions is in this report.

“It ended up being longer than anybody thought, which is a good thing, because it means there are a lot of options people have been thinking and talking about.” He spoke with Stanford Report about the reasons for the current report, some of the tools it examined and how it’s emblematic of a change in course for coral research.


How does climate change hurt coral?

Overheating is the biggest climate-related problem facing corals right now. Confronted with ocean heat waves, corals tend to spit out the internal algal symbiotes from which they get most of their energy. Then a large proportion of the corals die and crumble away. This is called coral bleaching. Coral bleaching around the world is one of the most obvious and alarming signatures of global climate change at the ecosystem level – you can see it from space.

A coral Palumbi and his lab have been studying in Samoa for years is named AH93. The first picture is the living, growing colony in 2011. The second is the colony bleached on the reef in August 2015. The third is the colony dead in December 2015. (Image credit: Courtesy Steve Palumbi)


What is the main finding of the report?

Our report very clearly says that what’s needed to keep coral reefs productive and of value to people in the future is solving the climate problem. Reducing carbon dioxide in the atmosphere simply has to be done in order for corals to succeed. But even if we instantly stopped putting CO2 in the atmosphere, we’d still have very damaged reefs because the climate is on a worsening pathway that will take decades to reverse. The report reflects a sense of urgency. We need to start helping corals now, so that as the climate gets worse – and it will inevitably get worse – we’re a little bit in front of the problem.


Can you tell me a bit about the range of tools you assessed?

There are 23 tools in this report. Several of them you might use on any kind of agriculture or aquaculture species. Others are so new, they aren’t available to us quite yet.

It’s an almost universal observation that there is variation in how different corals react to the same temperature, even in the same species. That led people to wonder whether we could grow corals that are more heat-resistant using selective breeding. Another strategy might be cross-breeding between species to generate hybrid vigor. Cryopreservation – freezing coral gametes to breed later – is another example. It’s a very common thing to do in domestic animal production and in plants but it’s just beginning in corals.

In terms of newer tools, the very first experiments showing success in using the gene editing tools CRISPR-Cas-9 have recently been reported out of John Pringle‘s lab in the genetics department of Stanford’s medical school. This represents a potential technology that is en vogue with the agricultural geneticists but there are a lot of barriers and knowledge that’d have to be gained in order to be able to use it in corals. By contrast, trying to genetically modify the symbiotes has been wildly unsuccessful so far – but people are still trying.


What is one intervention you researched that you think people probably haven’t heard of?

Symbiotes themselves come in a range of different types with some more heat-resistant than others. Very new work shows that you can have a coral fragment spit out its current crop of algae and then get it to take up more heat-resistant algae. That’s something we never really thought of before and means there’s a possibility of helping many of the corals that make up the reef framework.


What’s your overall sense of how well these tools might work?

“Our report very clearly says that what’s needed to keep coral reefs productive and of value to people in the future is solving the climate problem.”

—Steve Palumbi

Marine Biologist

The good news is that when you open the toolbox it is not empty. But the bad news is that none of the tools have been deployed successfully on the global scale. We know that if we plant more heat-resistant corals in nurseries, those nurseries are more heat-resistant. But this has only been done over scales of 100 meters or so – not kilometers or the thousands of kilometers that the Great Barrier Reef needs. Still, these advances based on existing heat-resistant corals are moving very quickly.

Other tools have only been tested in the lab or haven’t been tested at all: for example, the whole set of environmental interventions that could conceivably reduce heat or light levels in coral reefs. Very local little tests to cool water on coral reefs during heat waves were successful at preventing bleaching but it’s hard to know how to scale that up. Shading the corals is doable but shading an entire reef could cause more problems than it would solve. Another example is moving corals outside their normal range – it’s possible but it’s never been done because we’re very worried about the release of new diseases or competitors or predators or other potentially invasive species.


Are there concrete next steps for doing something with these findings?

If the only people in the world who know about these reports are the researchers, then we’re doomed. These findings have to get in the hands of the managers and the agencies and even local towns and villages that are sitting on top of coral reefs.

We discovered there’s a wide variety of different tools that are being used and developed in a wide variety of ways. Now the question is how do you decide which ones to try? How do you decide which ones to use? How do you evaluate the relative risks and the relative benefits? That is exactly the subject of the next report.


How does this report fit into the bigger picture concerning efforts to address climate change’s effects on corals?

Ten years ago, talking about these interventions was not on the table at all, even at major conferences in this field. Now there’s an almost universal sense of urgency about helping reefs survive. This report, for example, was put together by people from various parts of the world from different disciplines who were willing to dive into areas of biology that they didn’t have that much familiarity with – for which they had to spin up their knowledge base quickly. There’s this amazing sense that we all have to just jump in and try ideas and fail so that, eventually, someone comes up with the answers we need.

Palumbi is also a senior fellow at the Stanford Woods Institute for the Environment

Media Contacts

Taylor Kubota, Stanford News Service: (650) 724-7707,