Heat-Resistant Corals Could Help Save Reefs into the Future

Heat-Resistant Corals Could Help Save Reefs into the Future

Lately, a lot of ocean and climate change news talks about how our coral reefs are in trouble. Scientists estimate that almost all coral reefs will die off by the end of this century if we don’t take action to slow climate change and rising ocean temperatures. But just the other week, the BBC ran an article about how scientists discovered a reef in the northern Red Sea that is faring relatively well in the face of warming temperatures.

This reef in the Red Sea has avoided coral bleaching despite warming ocean temperatures, which have caused mass bleaching events around the world for the past few years. Scientists think one reason this reef could be so resilient is that its corals evolved in a warmer region of the ocean and then migrated to this part of the Red Sea where ocean temperatures are still below the corals’ maximum temperature.

To find out more about this spark of hope, our climate communications manager Cody Sullivan spoke with Dr. Steve Palumbi, a world-renowned coral scientist as well as Ocean Conservancy Board member, to find out more about heat-resistant corals and how they may help us conserve and restore reefs in the future.

And if after reading this you want to learn more about corals, Dr. Palumbi has produced several videos that are great places to start, such as: What is a Coral?, Four Kinds of Coral Reef and Life on a Reef.


Cody Sullivan: First off, hearing about that reef in the Red Sea was pretty exciting. But are there other examples of heat-resistant reefs or is that one more of an anomaly?

Steve Palumbi: The Red Sea reef is not an anomaly. It’s one in a series of warm water coral discoveries that’ve been happening around the world. My lab first saw examples of this type of resilience in American Samoa, where we’ve worked on a couple of parts of the reef system over the past ten years. In American Samoa, the warmest part of the reef actually had some of the most resilient corals we’ve seen. There are also examples of these types of reefs off Saudi Arabia, the Marshall Islands and across the whole archipelago around Palau.

CS: How do these reefs handle the warmer temperatures without bleaching and dying off?

SP: A coral can be heat resistant for four reasons:

  1. The coral is living in a warm part of the ocean and it has physiologically adjusted to withstand warmer water. This type of adjustment is also called acclimation, and while it makes corals more resilient it isn’t a permanent type of resilience that a coral could then pass on to its offspring.
  2. All corals coexist with a symbiont, which is another organism (typically algae in the case of coral) that provides food for the coral while relying on the coral for a safe place to live. Sometimes corals may have a more heat-resistant symbiont that then transfers some resilience to the coral itself.
  3. Corals may host microbes inside of them that allow the corals to be more heat tolerant. This possibility is the least well known, but it is an option.
  4. The coral itself might have just the right combination of genes that allow it to be more heat tolerant than other corals. This genetic reason is the only one of the four that is permanent and can be passed on from one generation to the next.

CS: You’ve studied coral resilience and genetics; can you tell us more about how you study coral genetics and find those resistant corals that can pass their resilience on?

SP: In our American Samoa work, for example, to figure out how resistant corals were to heat we would move the corals from place to place and see how they responded to the different temperatures. In Samoa we knew that the corals all had the same symbiont; we would break a coral into two pieces (which doesn’t hurt the coral, by the way) so we knew that the two specimens we moved around were physiologically identical. That way we could eliminate the first two reasons for why a coral could be heat resistant and therefore be able to conclude that it was most likely that any resilience we see is a result of genetics.

One of my students also looked at about 20,000 different coral genes to see which genes were associated with the corals that we saw best tolerating warmer waters. What we ended up finding was that there are a couple hundred genes in corals that transfer heat resistance. There isn’t just one single gene for living in warm water. This trait for heat resistance is more like a trait for human height, which is controlled by many genes as well as the environment.

CS: How can coral restoration and replanting projects use the discoveries scientists like you are making to help coral reefs into the future?

SP: We must notice that not all corals of the same species have the same heat resistance. Once you know that, coral restoration projects should keep track of the individual corals they’re using and how they react to nursery conditions. It’s a great asset, but also a pain in the neck. But with the research people are doing, restoration projects can look at each colony and which ones have different preferences or abilities that would be better suited for specific conditions out in the ocean.

Some of the best restoration programs are being run in Australia at the Australia Institute of Marine Sciences. They have the capacity and staff to do that type of careful work and track individual corals. Because they have the Great Barrier Reef, they have some of the best coral biologists in the world and are at the forefront of techniques, trials and this work at-large.

CS: We often hear in the news about how coral reefs could largely disappear this century as a result of climate change. But in light of discoveries like these resilient reefs and research such as that you carry out, do you see reasons for us to remain hopeful about the future of coral reefs?

SP: I think there really are signs of hope for coral reefs. There’s no question that the next 80 to 100 years are going to be bad for coral reefs as ecosystems. The loss of the value of coral reefs around the world will be the loss of a huge amount of storm protection, fish that people rely on for food and the island culture of the Pacific. A lot of that is almost inevitable at this point; and it’s really sad for our ocean and the communities it will hurt.

But, if we do stop emissions in the next couple of decades, the world will begin to turn around and get better. We’re trying to save as much as possible now so when it’s time for reef ecosystems to grow back that they have something to grow back from. The last couple of millions of years of coral evolution have produced heat-resistant versions of almost every species of coral that scientists have looked at. I’m absolutely convinced that we can make things better than they would otherwise be, if we can turn the corner on carbon emissions.

CS: As an ocean conservation organization, that’s very encouraging to hear. Lastly, you’re not only a scientist, but you’re also a Board member for Ocean Conservancy. As we move forward to try to help our coral reefs and the ocean more generally, what do you see as the role of organizations like Ocean Conservancy and how do Boards like ours help organizations achieve these goals?

SP: Organizations like Ocean Conservancy are there to keep bringing facts to the table. The facts of climate change are so powerful right now, being able to be there and make sure people don’t forget those facts and actually act on them is incredibly important. The staff at Ocean Conservancy is fabulous at taking detailed science and turning it into policy actions.

Then we have the Board which is a fabulous group of excited, creative and successful women and men who have determined they’ll turn their talents to helping Ocean Conservancy do what it does best: helping save the ocean. We’re a powerful cheering squad that provides support and guidance for the technical team at Ocean Conservancy who can do what we can’t. I’m really proud to be part of #TeamOcean as a board member.

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