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<\/a><\/p>\nBranching coral grows atop a metal structure in about 10 feet of water. Researchers planted it here as part of a project to try to restore a damaged reef off the coast of northwestern Palau.<\/p>\n
I\u2019m swimming down to get a closer look at the planted corals.<\/p>\n In the past two decades, governments, nonprofits, and even hotels around the world have dedicated hundreds of millions of dollars to replanting coral reefs<\/a> like this one. Reefs are among the planet\u2019s most endangered ecosystems: Rising ocean temperatures, pollution, and other threats have killed off an estimated 50 percent of live coral<\/a> globally since the 1950s.<\/p>\n Those steep losses erode the irreplaceable benefits that coral reefs provide. They go far beyond tourism. Healthy reefs lessen coastal flooding from storms like Bavi. They also serve as nurseries and homes for larger animal species, such as endangered sea turtles and valuable fish like snappers and groupers that people eat.<\/p>\n That\u2019s why so much time and money has gone into restoring these ecosystems globally. Including here in Palau. A different typhoon and warming waters had destroyed some of the region\u2019s coral many years ago, which caused the local fishery to decline, according to Sharp Sakuma, the governor of Ngaraard, a Palauan state where the coral garden is located. \u201cIt\u2019s our food,\u201d Sakuma said of fisheries. So a few years ago, he asked local researchers to help bring the reef back.<\/p>\n But reef restoration has a fatal flaw.<\/p>\n Rising global temperatures are heating up the ocean and fueling marine heat waves, which kill reefs. That means that much of the coral that people painstakingly plant often ends up dying months or years later \u2014 simply because the ocean is too hot. It\u2019s like planting trees to restore a forest that will soon burn in a wildfire. And this raises serious doubts about the role reef restoration can play in the recovery, and ultimate survival, of these iconic ecosystems.<\/p>\n The colorful antlers, mittens, and brains below me, however, were not your typical planted corals.<\/p>\n And they may offer a new reason for hope.<\/p>\n Palau is a diver\u2019s paradise, home to a rich diversity of colorful corals just below the water\u2019s surface.<\/p>\n These corals had all gone through what you might call a fitness test. In a lab on shore, marine scientists exposed them to extreme heat and scored them for their ability to tolerate warming. Corals on some of the metal stars here got top marks \u2014 they appeared resistant to heat. Those individuals may have more of a fighting chance at surviving as ocean temperatures rise.<\/p>\n These sorts of fitness tests for corals are inexpensive and unexpectedly low-tech: They take place in cheap, store-bought picnic coolers, like what you might bring to the park. But by helping researchers identify the hardiest corals, these tests could help overcome one of reef restoration\u2019s greatest challenges.<\/p>\n Subjecting corals to hot water in a plastic cooler may sound ridiculous. Until you consider the stakes and the circumstances: As the planet warms, simply protecting our beloved, life-supporting places is no longer enough to save them. Neither is restoring them to some former state.<\/p>\n To truly help coral reefs endure, we may actually need to reengineer them.<\/p>\n Scattered across a remote stretch of the Pacific is a collection of more than 300 islands, which, together, form the nation of Palau. Many of those islands are no larger than a small house. And because they\u2019re eroding at the base, they look as though they\u2019re floating above the ocean. When you\u2019re out at sea, it\u2019s easy to pretend that you\u2019re flying through the floating mountains of Avatar\u2019s Pandora.<\/p>\n Palau is an archipelago comprising some 340 islands powdered with trees. Erosion at the base of the islands makes it appear like they\u2019re floating above the ocean.<\/p>\n But the real magic is, without a doubt, underwater.<\/p>\n Palau is surrounded by a vast network of coral reefs, many of which are in near-perfect condition. The region has more than 400 coral species<\/a> \u2014 for comparison, the Caribbean has about 70 \u2014 which form the base of a thriving marine ecosystem. On just one weekend of diving there, I encountered close to 100 sharks, more than a dozen sea turtles, and three enormous manta rays. (In my more than 20 years of diving, I\u2019ve rarely seen such an abundance of sea life.)<\/p>\n In the last two decades, Palau has become an epicenter for research on how warming affects coral reefs. Part of that is practical: The country\u2019s abundant corals allow scientists to study how different species and populations respond to rising temperatures. It\u2019s also home to a well-equipped marine lab, the Palau International Coral Reef Center.<\/p>\n 1\/6<\/strong>Hawksbill turtle (Eretmochelys imbricata) with emperor angelfish (Pomacanthus imperator) and bigeye barracuda (Sphyraena forsteri) behind, at the Blue Corner dive site.<\/p>\n But there\u2019s also an urgent local need. Palau is deeply dependent on its coral reefs: Its fisheries and tourism<\/a> make up more than a quarter of the country\u2019s GDP. And while Palau is home to one of the world\u2019s largest marine protected areas<\/a> \u2014 which bans commercial fishing across 80 percent of its national waters \u2014 that does little to protect the reefs here from the existential global threat of ocean warming.<\/p>\n Why is heat such a dire problem?<\/p>\n One \u201ccoral\u201d is not a single animal but a colony of hundreds or thousands of individual animals, known as polyps. Those polyps are all nearly genetically identical. They grow the colony \u2014 the coral structure that you see on a reef \u2014 by cloning themselves over and over again.<\/p>\n Polyps fuel themselves, in part, by grabbing particles out of the water with tentacles (up close, polyps look a bit like sea anemones). But most of their food, and much of their color, comes from a kind of algae that lives within their cells. Like plants, that algae photosynthesizes. And it passes the solar energy it generates onto the coral, in return for nutrients and a place to live.<\/p>\n This partnership fails under extreme heat.<\/p>\n When the ocean is too warm, the algae malfunction, and the polyps kick them out. As a result, the corals lose their primary source of food and their iconic color. That\u2019s bleaching. A bleached coral is not dead but starving, and it will die unless the water cools back down.<\/p>\n A dead branching coral on a near-shore reef in northwestern Palau. Branching corals grow more quickly than big, bouldering colonies, yet they tend to be more susceptible to warming.<\/p>\n Yet there\u2019s another key detail here: Some corals seem to resist this heat-fueled bleaching. They appear naturally more tolerant to warming than their peers. And you can actually see this when you\u2019re snorkeling during a heat wave: Some corals will be bone white, whereas other colonies of the same species nearby will appear fully saturated. Heat tolerance is a trait with natural variation, like height or eye color in humans.<\/p>\n It\u2019s this detail that underpins efforts to make reef restoration less futile in a warming world. If scientists can find local corals that can tolerate warming, they can use them to regrow native reefs that might endure some degree of climate change, here and anywhere coral reefs can be found.<\/p>\n What scientists in Palau are trying to demonstrate is how \u2014 absent a naturally occurring heat wave \u2014 you can identify those heat-tolerant colonies.<\/p>\n On a mostly clear afternoon in July, days before the typhoon grazed Palau, I boated out to a shallow reef with Steve Palumbi, a marine ecologist at Stanford University. He\u2019s tall and thin and has white hair that he often pulls back into a short ponytail.<\/p>\n Once the boat dropped its anchor in the sand, Palumbi and I jumped in, along with three researchers from the Palau International Coral Reef Center (PICRC). I felt like I was swimming in a tropical fish tank. The water was clear and full of silvery fish. A carpet of colorful coral coated the seafloor. Every hole and crevice was occupied \u2014 by a giant clam, a spiky starfish, a sea cucumber, a furry crab. The reef was a giant apartment building with a cast of unusual tenants.<\/p>\n 1\/4<\/strong>Steve Palumbi pauses to take notes on waterproof paper while collecting pieces of coral for heat testing.<\/p>\n I followed Palumbi and the PICRC researchers over to metal structures on the reef that his team had built. They looked like sunken bed frames, and like those metal stars, they were covered in pieces of coral.<\/p>\n These corals are some of Palumbi\u2019s guinea pigs.<\/p>\n Over the last two years, researchers in his lab at Stanford have been subjecting them to a variety of different heat tests and scoring their performance. The concept is simple: Put the corals in a tank, crank up the temperature, and measure how quickly each one bleaches. The colonies that stay colorful as the temperature soars \u2014 the \u201cwinners\u201d \u2014 may be more tolerant to warming.<\/p>\n Why are some corals more heat-tolerant than others?<\/p>\n For years, scientists have been chipping away at this question. We now know, for example, that a polyp\u2019s genetics has something to do with it<\/a>; like height in humans, heat-tolerance is partly heritable and can be passed on from parents to their kids. The specific kind of algae<\/a> living in the coral tissue \u2014 its solar power-plant partner \u2014 matters, too.<\/p>\n Yet there are still big unknowns. Scientists still don\u2019t know exactly how the genes of polyps and algae may combine in some way to influence tolerance. In search of answers, a researcher in Palumbi\u2019s lab, Brendan Cornwell, is running corals through heat tests, and then examining the genomes of the winners and losers in search of clues.<\/p>\n There are several different ways to measure a coral\u2019s tolerance to warming in a lab. Some tests expose corals to moderately high temperatures over weeks, whereas others blast them with extreme heat over days, or even hours. Longer-lasting tests tend to better represent a natural heat wave \u2014 what corals will actually face in the years to come. But they\u2019re expensive, time-consuming, and require expertise. That\u2019s a problem for people who are racing to rebuild damaged reefs, especially in poor regions that lack fancy marine labs and funding.<\/p>\n Working with PICRC, the Nature Conservancy, and other partners, Palumbi\u2019s lab has been trying to demonstrate that the quick and cheap version of these heat tests \u2014 using picnic coolers to pressure-test corals over a few days \u2014 works well enough. They can help identify heat-tolerant corals and, thus, improve reef restoration, all within one work week, and on a low budget.<\/p>\n That afternoon, Palumbi was collecting corals from those metal frames to test at PICRC. Using wire cutters, Palumbi and the other researchers snapped off branches of coral from the individual colonies. Breaking fragments of coral off a colony is not unlike taking clippings from plants \u2014 the \u201cdonor\u201d colony continues to grow, even as parts of it are removed.<\/p>\n PICRC researcher Lauren Piot holds onto a metal rack full of coral at a research site in eastern Palau.<\/p>\n A coral fragment.<\/p>\n A plastic bin full of coral fragments that the researchers will test at PICRC.<\/p>\n After filling plastic bins with dozens of coral fragments across three species, the researchers brought them to the boat, loaded them into a large container full of seawater, and then we headed back to shore.<\/p>\n It is hard to put a price tag on coral reefs, but those who have tried say it is quite a lot.<\/p>\n The authors of one study published in 2024 estimated that reefs in the Asia Pacific<\/a>, which includes Palau, Australia, and Indonesia, among other countries, contribute about $25 billion a year on average to the region\u2019s economies for their role in supporting fisheries and tourism alone.<\/p>\n One afternoon I went spearfishing with Genevieve Rechelbang, a well-known fisher in the northeastern state of Melekeok.<\/p>\n Rechelbang spears a rabbitfish.<\/p>\n The PICRC boat we were on, anchored at one of Palumbi\u2019s research sites, off the east coast of Palau.<\/p>\n That doesn\u2019t include the damage that reefs offset during tropical storms. Coral reefs are self-regenerating seawalls that can reduce wave energy \u2014 dulling the fiercest brunt of a hurricane making landfall, for example \u2014 by an average of 97 percent<\/a>. In the US, economists estimate that reefs save the country more than $1.8 billion a year<\/a> just in avoided flood damage. Globally, the cost savings from coral reefs<\/a> are far higher.<\/p>\n So it\u2019s no surprise that people are so eager to rebuild reefs when they collapse.<\/p>\n To restore these ecosystems, people typically harvest fragments of coral from the wild and grow them in a tank on land or in a \u201cnursery\u201d in the ocean. Then they plant them, one piece at a time, on the seafloor, often using an adhesive putty<\/a>.<\/p>\n Reef restoration has grown into a global project of enormous scale: A network called the Coral Restoration Consortium counts more than 900 reef restoration efforts worldwide<\/a> led by more than 350 organizations. By one estimate, groups have spent more than $250 million on reef restoration<\/a> over roughly the last decade.<\/p>\n But as important as those efforts may be, many of them haven\u2019t worked \u2014 they haven\u2019t actually helped coral reefs grow back<\/a>. \u201cShow me a square mile of reef that has been [successfully] restored,\u201d Palumbi said. \u201cThere isn\u2019t one.\u201d<\/p>\n At the heart of that failure is climate change: Prolonged bleaching kills off much of the planted coral, undoing a tremendous amount of effort.<\/p>\n Dead branching coral covers the seafloor near the planted garden I visited during the typhoon.<\/p>\n A mix of dead, algae-covered branching coral and brightly colored colonies that still appear healthy.<\/p>\n One of the most extreme examples of this is in Florida. In the last three decades, organizations have planted tens of thousands of corals in the Florida Keys, which is home to the world\u2019s third-largest barrier reef. I visited in 2022 and saw the progress of restoration firsthand \u2014 there were beautiful fields of planted staghorn and elkhorn, two federally threatened coral species. Some colonies were more than a meter wide. I wrote a story about how it was reviving Florida\u2019s reef<\/a>.<\/p>\n Then in summer 2023, a record-breaking heat wave struck<\/a>. The reefs turned a ghostly white<\/a>. And eventually, nearly all of the staghorn and elkhorn coral<\/a> in the Florida Keys \u2014 including the vast swaths of replanted corals \u2014 died, becoming functionally extinct<\/a>. It was one of the more devastating things I\u2019ve seen in my time covering the biodiversity crisis<\/a>.<\/p>\n There are similar examples from around the world \u2014 in Colombia<\/a> and Costa Rica<\/a>, for example, along with Indonesia<\/a> and the Seychelles<\/a>.<\/p>\n It\u2019s not that restoration groups are unaware of this problem. Scientists have been studying bleaching for many years in search of solutions. In Florida, researchers are testing out what happens if you cross-breed corals from South Florida<\/a> with colonies from a warm reef in Honduras, which have a natural ability to withstand higher temperatures. Perhaps their hybrid babies will be more likely to survive the next heat wave. But most of these approaches are time-intensive, costly, run by teams of PhDs, or stuck in the lab.<\/p>\n Steve Palumbi keeps track of individual coral fragments as he prepares them for a round of heat testing.<\/p>\n \u201cThe lab science is cool,\u201d Palumbi told me. \u201cBut it\u2019s going too slowly. We don\u2019t have time to wait.\u201d<\/p>\n The outdoor research space at PICRC looked like a typical marine lab \u2014 a labyrinth of pipes and pumps and, of course, tanks full of sea creatures, which in this case included corals, urchins, and giant clams that would abruptly close if you got too close. It looked appropriately science-y. With the exception of one wooden shelf. On it were eight blue and red plastic picnic coolers, in which Palumbi\u2019s team is doing the bulk of its heat testing.<\/p>\n After returning to shore with bins full of coral fragments, Palumbi put some of them into the coolers, which were fitted with small heaters and pumps. The water inside was around 30 degrees C (86 degrees F). That\u2019s the average high temperature for waters in this region, and the baseline for the test he was about to run.<\/p>\n Then Palumbi, rather unceremoniously, cranked up the dial.<\/p>\n The heat tests Palumbi uses are a bit DIY \u2014 small Coleman picnic coolers.<\/p>\n This low-tech approach helps keep heat testing cheap and accessible to a range of environmental groups, including those in poorer regions.<\/p>\n Over each of the next four days, the water in half of the coolers would hit a higher temperature, before returning to the baseline of 30 degrees. On day one, for example, it would reach 34; on day two, it would hit 35; and so on. And each morning, Palumbi would assess the fragments for bleaching. Although these tests run for only a few days, they\u2019re meant to mimic what some corals might experience at low tide during a heat wave, Palumbi said.<\/p>\n I visited the lab early one morning, after just one day of heat stress \u2014 after the coolers had reached 34 degrees. Palumbi laid the fragments out on a white grid to evaluate their color, ranking them from one (no bleaching) to five (fully bleached). They were shaped like twigs and still had their normal orangy brown color. No bleaching yet. By the next morning, however, the corals appeared more varied: Some were starting to pale and others remained saturated.<\/p>\n On the last morning of the test \u2014 after the coolers had reached 37 degrees, or close to 100 degrees F \u2014 nearly all the fragments were white, resembling cauliflower florets. They had expelled their algae. And yet a handful of the fragments still appeared mostly brown. Even after getting blasted by extreme heat, they hadn\u2019t bleached.<\/p>\n \u201cThose are the champions,\u201d Palumbi said.<\/p>\n Palumbi holds up two coral fragments that went through heat testing. The one on the left, as you might have guessed, is bleached.<\/p>\n He was testing three species of coral in a genus called Acropora, which are branching corals \u2014 those that grow a bit like trees. This is a species known as Acropora hyacinthus.<\/p>\n During the heat tests, researchers score the coral fragments using different methods, including a simple visual assessment for bleaching. You can see here how some corals have bleached much more than others.<\/p>\n Palumbi believes that quick heat tests like this stand to benefit restoration projects across the tropics. The equipment, including four coolers, costs less than $1,000, according to Courtney Klepac, a researcher in Palumbi\u2019s lab, who studies heat testing. Groups that are rebuilding reefs can essentially run the corals they harvest through these tests, and then only plant the champions.<\/p>\n A drone view of Palumbi and PICRC researchers collecting fragments for heat testing.<\/p>\n That\u2019s precisely the idea behind a project Klepac leads called the Coral Futures Academy. She\u2019s been helping environmental groups across the Pacific integrate these low-overhead heat tests into local reef restoration efforts. And these actually include the coral garden I snorkeled during the typhoon: All the pieces of coral there had gone through similar heat tests.<\/p>\n As promising as this approach sounds, however, there is an important caveat: These tests are only useful if they actually predict which corals are more likely to survive under real-world warming. And so far, scientists haven\u2019t proven that.<\/p>\n Previous studies<\/a> comparing short heat tests to those that are longer and more faithfully replicate a real heat wave show mixed results; the winners of one are often not the winners of the other. It suggests that surviving a short blast of heat requires different skills than withstanding warmth that lasts for weeks.<\/p>\n Some researchers have also measured what happens to corals<\/a> that went through an even faster one-day test after they were put in the ocean and then experienced a real heat wave. The champions in those rapid tests were not always more heat-tolerant in the wild.<\/p>\n Ilan Bubb, a marine biologist at the University of Amsterdam who\u2019s studied heat tests, says it\u2019s like trying to predict a person\u2019s marathon time based on how well they perform in a sprint. \u201cWe know there\u2019s some correlation there, but how good is that correlation?\u201d he said. \u201cHow much information you can get about that marathon from a hundred-meter sprint is still just undetermined.\u201d<\/p>\n Palumbi, Klepac, and their colleagues have been exploring this question, too. They\u2019ve compared bleaching scores from heat tests that last for three or four days to those that last for roughly two weeks. The results appear to be similar, Klepac said: On average, the same corals resisted or succumbed to bleaching in both experiments.<\/p>\n Klepac has also studied what happens to heat-tested corals when an actual marine heat wave hits. At the coral garden I visited with those metal stars, PICRC researchers planted the heat-test winners as well as the poorer performers, as a point of comparison. And as Klepac\u2019s unpublished research shows, the winners of the short heat tests survived better during a bleaching event in Palau in 2024, compared to the losers.<\/p>\n \u201cI am probably one of the few people that you will talk to that kind of low-key gets a little excited for bleaching events,\u201d Klepac told me. \u201cIt is a very true test of what we\u2019ve been doing. If we\u2019re trying to market this approach, I want to feel confident that what we\u2019re prescribing actually works.\u201d<\/p>\n Palumbi and PICRC\u2019s Uly Olsudong check their work.<\/p>\n There are other drawbacks to this testing approach. For one, it relies on a visible trait \u2014 whether a coral resists bleaching or not. That trait, however, doesn\u2019t always indicate whether the coral has the genes to resist bleaching. The colony may have just been healthier going into the test than its peers. Two runners, for example, might get different times in a 100-meter sprint, not just because of their genes but because of how much rest they got the night before.<\/p>\n This matters when you\u2019re trying to rebuild a reef: Typically, you want the coral colonies you plant to eventually reproduce and create heat-tolerant babies. That only happens if the parents have heat-tolerant genes.<\/p>\n And there are other traits that corals need to survive, beyond the ability to withstand warming.<\/p>\n \u201cIt\u2019s not just about heat tolerance,\u201d said Liam Lachs, a coral researcher at University of Queensland in Australia who has extensively studied the value of different heat tests.<\/p>\n Read more Vox reporting coral reefs<\/p>\n By only planting the corals that perform well on these heat tests, you might miss colonies that have other important strengths, such as the ability to withstand disease. In fact, future research may reveal that testing corals for one of these other traits may ultimately be a better predictor of their survival in the era of climate change, says James Guest, a reef ecologist at Newcastle University in England.<\/p>\n Palumbi readily admits that the short picnic cooler tests are not perfect. But the important question, he says, is whether they are good enough \u2014 good enough to start using them now to help reefs as the science around fitness testing gradually improves.<\/p>\n That much is clear, he says, and several other researchers I spoke to agreed. While the utility and accuracy of short heat tests is not yet proven, people who want to rebuild reefs should still use them, they said. For restoration, there simply aren\u2019t many better alternatives.<\/p>\n \u201cIt\u2019s quick, it\u2019s easy to do, people can apply it relatively straightforwardly, and it offers some kind of test,\u201d Guest told me. \u201cComing up with these practical approaches makes sense.\u201d<\/p>\n The sun was still low in the sky as Palumbi and I strapped on our tanks and weights and plunged into the ocean near one of Palau\u2019s floating islands.<\/p>\n Sinking down felt like descending onto an alien planet. There were rolling hills of branching coral and stacks of plate coral the size of merry-go-rounds. Schools of colorful fish flew over them, like flocks of birds across a woodland.<\/p>\n The seafloor was utterly covered in coral at this shallow dive site in southern Palau.<\/p>\n The colors were spectacular.<\/p>\n Palumbi cruises over a massive coral colony that was likely hundreds of years old.<\/p>\n Toward the end of the dive, we came across a single coral colony as large as a suburban home. The surface was lumpy and covered in what looked like large bulbous fingers. Given its size, the coral was likely at least three hundred years old.<\/p>\n When we were back on the boat, I asked Palumbi what he thought of the reef. \u201cIt doesn\u2019t get better than this,\u201d he said.<\/p>\n Isn\u2019t it arrogant to think we can recreate, or even fortify, something as complex as a coral reef?<\/p>\n There could have been 200 species of coral on this one reef alone, Palumbi said, some of which may still be unknown to science. If this is what coral reefs are supposed to look like, even our best science probably can\u2019t recreate them.<\/p>\n It seems like our time would be far better spent trying to prevent reefs like this from dying in the first place. \u201cWe all know that we have to solve the bigger problem,\u201d Guest said. \u201cIf we don\u2019t reduce carbon emissions and we don\u2019t deal with climate change, nothing we do is going to help corals.\u201d<\/p>\n Palumbi swims near a school of bigeye trevally as a gray reef shark passes by.<\/p>\n A carpet of light purple branching coral.<\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n