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Palau’s Improbably Healthy Coral Reefs

Why acidic waters haven’t killed Palau’s vibrant coral could help save many reefs from catastrophe.

ByJoshua SokolNOVA NextNOVA Next
Palau’s Improbably Healthy Coral Reefs

Flippers first, I splash into the year 2100. I’m snorkeling with coral ecologist Hannah Barkley in blue-green Nikko Bay, where limestone mushrooms jut from the water to form the kind of terrain you’d expect around a Bond villain’s lair. Here in the Rock Islands of Palau, natural conditions offer a glimpse into the Pacific Ocean expected by the end of this century—when it’s acidified by dissolved carbon dioxide from an overladen atmosphere. By all rights we should see a dire, climate-changed wasteland.

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But the corals here look fine.

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Reefs link Palau's striking Rock Islands.

Better than fine. It’s gorgeous, an explosion in a paint factory. Tropical fish flit between tumorous yellow mounds, rusty ginger roots, and red-orange pancake stacks topped with stalactites. Some aged coral clumps are tipped to the side like fallen trees, their bone-white bases exposed, but new shoots are springing up perpendicularly toward the sun. When we surface, Barkley is grinning ear to ear.

It’s Barkley’s sixth time in Palau, and the seventh trip to the Micronesian country for Anne Cohen’s lab at the Woods Hole Oceanographic Institute in Massachusetts, where Barkley is a Ph.D. student. What began as a fact-finding mission in preparation for climate change has blossomed into something bigger, more prognostic, and more hopeful.

The reefs within Palau's bays offer a preview of how corals around the world might respond to ocean acidification.

The bad news first: over the next century of climate change, all coral reefs will have to contend with two inextricable, inexorable pressures. One is global warming, where hotter ocean temperatures will lead to the wide-scale “bleaching” of reefs. The second is ocean acidification. About a third of the carbon dioxide we add to the atmosphere ends up mixing with the seas, souring the oceans for the many creatures that scaffold their squishy bodies with hard shells made from the mineral aragonite.

But to their surprise, Cohen’s team has found that the corals in Nikko Bay and a few other naturally acidified Rock Island sites seem to be shrugging off this sneak preview of the coral-reef apocalypse. If these locales can be preserved, ecologists think they might have a better chance of surviving climate change than anywhere else in the Palauan archipelago.

Today, Nikko Bay, with its warm, acidified water and healthy corals, sits precariously at the intersection of three worlds. Scientists are forging on with their studies, engrossed in the minutiae of what makes these corals special, conservationists are holding it up as a reason for optimism, and Palauans, tied to the sea, are trying to save these reefs while they still can.

Anne Cohen describes the discovery in Palau.

A single event binds them all together. In 1998, heat waves from a vicious El Niño event devastated reefs across the globe. The sudden loss of 16% of the world’s coral cast a shadow into the future, toward what some experts are calling the “end of reefs.” But this cataclysm also inspired conservationists to look for pockets of climate-change resistance, and it pressed Palau to invest in the very research infrastructure that would make Cohen’s later work possible.

And in its wake, the El Niño brought the first hints that the bays between Palau’s Rock Island might be worth a close look.

Born in a Crisis

Yimnang Golbuu, Cohen’s main Palauan collaborator, grew up in a neighborhood with one black-and-white TV. He spent his childhood outside—fishing, swimming, hunting small geckos in the forest—before crossing the Pacific to major in biology at the University of California, Davis.

Compared with Palau, Golbuu tells me, the winters in California were intolerable. After surviving the cold temperatures, the ecological train wreck of Guam, where he subsequently went for his master’s degree, was distressing. One thought kept him going: “I’m going to come back to Palau,” Golbuu says.

But shortly after he returned, the reefs he loved went to hell. The El Niño of ’98, like Niños in other years, saw a break in the winds that push water across the Pacific. Stagnant currents changed weather patterns on a global scale, subjecting tropical reefs worldwide to weeks and weeks of warmer-than-usual water.

Yim Golbuu
As CEO of the Palau International Coral Reef Center, ecologist Yimnang Golbuu is the main force behind reef conservation in Palau.

In 50 countries, the photosynthetic algae that live inside corals and help feed them short-circuited in the heat, releasing destructive free radicals. Perturbed by the conduct of their tenants, the host corals expelled their algae to limit the damage.

Normally, the turquoise shoals between Palau’s Rock Islands show dark patches of coral against the sandy bottom. When the bleaching hit, these shadows turned white. The corals no longer had their algae; the colorful pigments inside were gone. As a result, giant swaths of these bleached corals starved and died.

On land, Palau was stricken by drought. The trees that jostle to fill every nook and cranny of the Rock Islands wilted, repainting Palau’s most scenic, unique landscape in rustlike tones. Groundwater in the populous, porous karst island of Koror dried up, forcing residents to get their water from the volcanic island Babeldaob.

In the face of this climate-related hardship, the need for reef conservation and research in a nation so dependent on marine resources could no longer be ignored. Three years after the crisis, the Palau International Coral Reef Center, also known as PICRC, was born. Palau had beat out several other Pacific countries for funding from Japan.

Once this research apparatus was in place, another consequence of the disastrous bleaching came into focus. Surveyors noticed a strange pattern when they started monitoring the nation’s reefs. “We could see that some of the sites just are doing better than others,” Golbuu says, over his desk. In 2012, Golbuu became perhaps the first Palauan to get a science Ph.D. It was covered in the newspaper, turning him into a local celebrity. We’re speaking in Golbuu’s air-conditioned office on the second floor of PICRC, where he is both CEO and head researcher.

Not all the coral had been hammered. There were still spots that looked more or less intact. “That kind of gave us a clue that things are different in these different sites,” he says.

A healthy reef slope off the coast of Palau

But because monitoring hadn’t yet begun at the onset of the El Niño event in 1998, there wasn’t a clear explanation for the healthy patches. Were some corals just bouncing back faster? Had the temperature not risen as high in those sites, causing less bleaching? Or had the corals themselves stubbornly resisted the heat?

A smaller bleaching in 2010 helped settle the question in favor of that last—and perhaps most intriguing—possibility. PICRC researchers went out and surveyed 80 coral communities across the archipelago. As before, some sites had bleached more than others. But how a spot fared didn’t seem to be explainable by records of temperature.

Some reefs that didn’t bleach had been even hotter than reefs that did, showing that mild weather wasn’t saving these corals. Golbuu suspects that the harsh environment had made the corals tougher. “And now these are the same sites that Anne [Cohen] is finding,” he says. “These are very acidic sites.”

Cohen herself first came to Palau in April 2011, backed by the Nature Conservancy, an environmental organization headquartered in Arlington, Virginia. In yet another thread tracing back to the ’98 bleaching, Cohen was offered several Pacific locations to visit; she chose Palau because of the research infrastructure that had sprung up in response to the crisis.

Cohen had heard that the enclosed bays had proved resistant to bleaching. And as a specialist in ocean acidification, she had a hunch that these same locales might also be responding to unusual chemistry.

Palau’s Rock Islands, the 20-million-year-old backbones of ancient coral reefs, provide a pinball machine’s worth of obstacles for ocean water that trickles through toward the innermost bays. In Nikko Bay, where corals had weathered the ’98 bleaching, water is trapped for months on end.

In these conditions, Cohen knew that the corals themselves could change the water chemistry. To build a skeleton, corals pull calcium and carbonate ions from the water and knit them into sturdy crystals of aragonite. This process is known as calcification. Just as breathing exchanges oxygen for carbon dioxide, slowly spoiling the air in a closed space, calcification draws carbonate out of the water, making the process progressively harder. And the corals are literally breathing, too, which adds more carbon dioxide, which in turn acidifies the water even more. Carbonate gets even harder to come by.

Ocean acidification makes it increasingly difficult for corals to build their skeletons.

In the fall of 2011, Cohen sent a postdoctoral researcher, Katie Shamberger, and her grad student Barkley to test the water in those enclosed bays. It was true exploration, Barkley recalls. “We basically looked at a map and said, ‘OK.’ Where can we go that looks like it might be interesting?” Even after they took the water samples, months passed before they knew how extreme conditions in the bays really were. The eureka moment happened not in Palau, but back at WHOI, after the samples were analyzed.

Barkley can still picture a beaming Cohen walking into the lab to announce that Nikko Bay was significantly more acidic than the tipping point expected to mark the end of reefs. “I was like ‘No way!’ ” Barkley says. Having first seen Nikko Bay’s vibrant corals in person, it was hard to believe. “It was wow ,” Cohen recalls. “These reefs are at 2100 A.D. These reefs are in the future.”

Seeking Refugia

As Palau was responding proactively to the ’98 bleaching crisis, the Nature Conservancy embarked on a hunt for refugia, or reefs that might be least vulnerable to climate change. And in a coincidence almost too good to be true, the idea that led to this new strategy came in the Rock Islands of Palau.

Rod Salm, Cohen’s backer at the Nature Conservancy, is the well-spoken, well-traveled director of marine conservation for the Asia Pacific region. His resume is a naturalist’s fantasy: Mauritius, Sri Lanka, India, Pakistan, and the Seychelles with the World Wildlife Fund in the 1970s; a doctorate studying the Chagos Archipelago in the middle of the Indian Ocean; then a stint in the new world, followed by four years in Indonesia and eight years in Oman.

Then, in 1999, when Salm was stationed in Nairobi, an otherwise ordinary moment turned into a revelation. He was helping his daughter with a high school research project. Together, they drove to the Kenyan coast and chose a long, thin island running north to south. The east side faced the ocean, catching the morning sun; the west side was sheltered, with mangroves nearby and motes of sediment twinkling in the light each afternoon. This being just after the 1998 El Niño, Salm helped his daughter look for bleaching. Corals on the east side? White as bone. On the west side? Normal.

It was puzzling. Later that year, Salm began travelling to coral reefs across the Pacific for his new job with the Nature Conservancy to survey the El Niño’s aftermath elsewhere: Indonesia, Papua New Guinea, the Solomon Islands. “I began suddenly to see patterns,” Salm says, “particularly in Palau.”

His epiphany happened at Palau’s Cemetery Reef, where the corner of one of the Rock Islands arcs down to meet the water’s surface. Underneath, the slope continues, with green vegetation replaced by foliose corals the color of yellow ochre, stretching like giant sheets of lichen. At least, that’s how it looked in January 2015. When Salm first visited after the bleaching, all the corals were dead.

At the time, Salm had swum toward the island, over whitewashed corals and rubble, until he was halfway under the circumferential groove cut into each of the Rock Islands by grazing mollusks. Once his pupils adjusted to the shade, “Suddenly I noticed that the corals under my fins were dead and the ones under my mask were alive,” he says. “That’s when it hit me.”

The Rock Islands' overhangs provide just enough shade to stave off bleaching.

The shade was saving the corals. It was embarrassingly obvious. It explained what he had seen in Kenya with his daughter: the sunnier side of the island had bleached, while the shaded side, with murkier water, had not. Heat plus bright light could cause the photosynthetic algae to release free radicals, causing corals to bleach. During heat waves, shadier places might stand a better chance. So might places where heat waves were buffered by deeper, colder water, an idea first suggested by researcher Peter Glynn in 1996 .

The El Niño of ’98 had been a wakeup call to the threat posed by climate change, yet it left managers of marine protected areas with a sense of helplessness. Protecting reefs from humans was one thing: They could limit fishing, restrict where boats could anchor, oppose coastal development. Global warming was different, almost unstoppable. Neither coral scientists nor reef managers knew how deal with it.

But here was hope. While many coral-reef scientists were studying the death and destruction of ’98 like photographers documenting war atrocities, Salm’s reaction was to pour resources into finding and studying the corals that hadn’t bleached. Managers would have the best chance to save these reefs.

Salm first presented his idea in 2000 at the International Coral Reef Symposium in Bali. It struck a chord. Billy Causey, now a director of marine sanctuaries at NOAA, then superintendent of the Florida Keys sanctuary, commented that natural refugia could explain the bleaching pattern he had seen in the Keys. Afterward, the World Wildlife Fund and the Nature Conservancy put down money for further research. A new paradigm had been born, balancing optimism with pragmatism. But there was little time to celebrate.

A close-up view of coral polyps

By 2005 and 2006, scientists had grown increasingly concerned about the impact of anthropogenic carbon dioxide on ocean chemistry. Researchers, having seen corals struggle in aquarium tanks at low pH, could extrapolate out to a tipping point when the world’s reefs would dissolve faster than they could calcify. Algae would fill in the gaps. The world was on a “slippery slope to slime,” wrote coral ecologist John Pandolfi.

Coral bleaching had been a shock when it first struck, a problem nothing in the conservationist toolbox could address. Strategies had to be developed after the fact. Yet this time, with ocean acidification, they had advance warning. The plan was to “have a jump on it when it hit,” Salm says.

Anne Cohen explains why ocean acidification can only be solved through international cooperation.

In 2008, Salm convened a meeting of scientists and conservationists in Honolulu. Together, they crafted a strategic response to ocean acidification, which one attendee aptly described as osteoporosis of the reef. Among their recommendations: to search for biodiverse reefs that might be less vulnerable to ocean acidification.

Thanks to Salm’s work, one method for hunting down climate-change refugia—seeking out places resistant to heat waves—already existed. But it applied to bleaching, and acidification has a different profile. Bleaching happens in pulses, when waves of hot water wash over the reef. Ocean acidification is most often a steady pressure. They obey different oceanographic rules, too. Take the Galapagos, for example. There, the upwelling of cold water helps corals resist bleaching, but cold water also holds more carbon dioxide, making it more acidic. In other words, a refuge for one might not protect against the other.

Salm met Cohen, an expert in carbonate chemistry and ocean acidification. He pushed her toward Palau, where Golbuu offered plenty of support, and where a wide range of habitats were thrown together in close proximity. And there they found far more than they’d bargained for.

Picking Winners

After Barkley and I get out of the water in Nikko, we head to another acidified yet healthy coral community in Palau, this one in Risong Bay just to the southwest. We’re pelted by angry pellets of rain, the boat bouncing jarringly over the waves.

As the boat slows to traverse a narrow channel, the trees above are nearly touching, their shadows reflected on the water’s surface with yellow boulder corals below. The boat emerges into a clearing, the Rock Islands curving around us. This is Chiropsalmus basin, named for a box jellyfish. Cohen’s team calls it the Jacuzzi.

Using a GPS device tied onto a buoy, Barkley and technical diver Pat Lohmann put on SCUBA gear and map the outlines of the coral growing underneath us. I snorkel above, thinking about refugia, wondering whether I’m swimming in one.

Hannah Barkley
Hannah Barkley prepares for a dive to collect samples.

When I ask Barkley whether Nikko Bay and Risong’s Jacuzzi are truly refugia, she refers me to the Nature Conservancy’s Elizabeth Mcleod, who works with Salm. Mcleod, with a measure of caution that’s common among ecologists, gently resists the poetic notion of refugia in favor of hard data. “I would be uncomfortable if any scientist says that we know that this area is definitively a refuge,” she says.

Perhaps it helps to unpack the idea of a refuge, where creatures survive and then go forth to repopulate other areas. In Salm’s writings on climate change, he breaks down the search for “less vulnerable” spots into a few dimensions. First is avoidance: a particular place that is entirely spared from adverse conditions. Considering that warming and acidification are both global in scale, it won’t be easy to find reefs that can avoid them. Then there’s resistance: the ability of corals to experience heat waves and not die, or to live in acidified waters and keep growing. Resistance could be innate, the province of hardened, tough corals, as Cohen suspects is the case in Palau’s acidified bays. Or it could be environmental, like the shade Rod Salm saw in Kenya—which may have also saved Nikko Bay’s corals from bleaching. It’s hard to untangle. And last is resilience, or a reef’s ability to grow back quickly and to send its larvae far and wide.

Presently, with the worst of climate change still to come, reef refugia seem distant and abstract. But the ideal of a refuge—the one weapon reef managers have against climate change, save a reduction in carbon emissions—is still on the horizon. Perhaps Palau’s bays will pan out as climate change refugia, or perhaps what researchers learn in Palau will help them find refugia elsewhere. Knowing for sure will take time, which there isn’t much of.

There’s another way to put it, one that acknowledges a fundamental truth: conservation costs money, both to fund the research and to commit to saving a place. On the day I spoke to Salm, he mentioned spending an hour and a half on the phone with a donor. The donor, about to give a talk to students on the subject of winners and losers in business, intended to draw heavily on Salm’s philosophy. His idea was that since climate change conservation—and perhaps life—are inherent gambles, it makes sense to bet on proven winners.

Back at the Jacuzzi reef, we climb out of the water, then return to Nikko Bay so that Barkley can take water samples. As we leave, beside two islands in the middle of the bay, we see a boat tugging an inflatable banana straddled by four whooping Asian tourists.

“This is your refugia?” I say to Barkley, raising my voice over the engine and the wind. She laughs and yells back at me: the tourists could be doing worse.

The Other Threats

On my last night in Palau, Barkley and I meet for dinner at Taj, Palau’s surprisingly good Indian restaurant. “The first time I jumped in Nikko Bay it was just breathtaking,” she says. The reef was more colorful, rich, and diverse than any reef she’d ever dived on, and this was before the team knew how acidified it was. Learning that these corals were living in extreme conditions made it all the more amazing.

By now, thousands of water samples, numerous measurements, and myriad experiments over the seven trips to Palau have left the team confident about the response of corals to conditions in places like Nikko Bay. In the acidified spots, coral cover is high, diversity is high, and the reefs appear to be healthy. The problem lies in what to make of these facts.

“It’s really easy to assume that oh, well, Palau’s doing fine. Reefs don’t care about ocean acidification,” Barkley tells me. The team has been careful to avoid saying anything like it. They haven’t even promised that they’ve found refugia. But Barkley still feels the work on Nikko Bay can be a source of hope. It means that somewhere, corals can survive these hostile conditions.

Outside critics are in qualified agreement. Katharina Fabricius, a coral ecologist at the Australian Institute of Marine Science, thinks that corals in locations like Nikko Bay are healthy only because the bays are so sheltered from storms. She also worries that despite Nikko Bay’s diversity, the main reef-building corals are absent—a claim Cohen’s team hopes to parry in a new study to be released in the journal Science Advances in June. Whether or not the Palau results are an optimistic findings “depends on how clear the caveats are expressed,” Fabricius tells me.

Nikko Bay in Palau

Barkley is working with Salm and Mcleod, who want a map of carbonate chemistry across the Palauan islands to compare with satellite data from elsewhere. “We need to understand: what are those patterns?” McLeod says. “How do we identify those potential refugia across the archipelago without having to jump in the water and sample every coral?” Barkley’s map, once produced, will inform searches for refugia around the world.

Using satellite images, Barkley has already found another place with a landscape similar to the Rock Islands, this time in Indonesia. Perhaps the pitted limestone islands there harbor acidification-resistant corals, too. But we’ll have to wait to find out—a scouting trip planned for the spring of 2015 was scuttled when obtaining permits proved a challenge.

In the meantime, Barkley’s goal is to hand Golbuu and Palauan officials a stack of maps that show pH and climate change tolerance across the island system. That would indicate which places she thinks have the best chance of surviving ocean acidification over the next century.

But as Golbuu told me in his office, the lobbying to protect the acidified Rock Island bays has already started, even before Barkley’s comprehensive recommendation comes in. Nikko Bay is at particular risk because it is close to Palau’s population centers, making it more vulnerable to the traditional threats to reefs: pollution, development, and sediment runoff.

These corals “might survive the end of this century,” Golbuu says, “but before then we’ll kill them with all the activities we do on land.” Each year, Palau hosts more than 100,000 international tourists, over five times as many visitors as the nation has full-time residents. Even the most remote, pristine dive sites are ringed with tour boats.

Development projects, including a new highway that rings the large island of Babeldaob, are threats to the same inshore reefs that may be most resistant to climate change. A few Palauan reefs, which survived the ’98 bleaching and might have been promising refugia candidates, have already been wiped out by the sand and dirt washing away from building projects.

On the day we spoke, Golbuu was weighing how to respond to the chief of Ngermid, the village bordering Nikko Bay. Palau’s traditional chiefs, who wield what he calls considerable “non-Western” power in parallel to the country’s modern political system, were very supportive of protecting Nikko Bay, he says, citing a concept called bul that provides the ethos for Palauan conservation. A bul , a moratorium on certain behaviors, can be used to let a tapped-out ecosystem rest. The local chief had requested details on why the place was special, but Golbuu was worried that the highly technical paper authored by Shamberger, the postdoc in Cohen’s lab, would need some explaining.

For the most part, Golbuu is waiting to hear back from the state legislature. “What I told them is right now Nikko Bay is treated like any other Rock Island in Palau,” he says. “But it’s not. It’s very special. So all we are asking you is: try to treat it differently.”

Palau's reefs are among the most diverse ecosystems in the world.

The legislature is dragging its feet, but the efforts to raise awareness have already helped, Golbuu thinks. A legislator checked with him after hearing a proposal to bring some sort of tourist submarine into Nikko Bay. Not here, Golbuu recommended, and the proposal was rejected.

As Barkley and I finish picking at the remnants of our dishes, I put the same question to her that preoccupies Golbuu. Just how heartened should we be about Palau’s special places? Can they last?

Barkley brings up qualifiers. There’s the dump near Nikko Bay, which may not be properly sealed. There’s the sewage outflow. There are those tourists, she says, joking about them running the banana boat into the reefs. But if those threats can be contained and these corals protected, she says, “they have probably the best chance of any of Palau’s reefs of surviving climate change.”

The Palauan Way

Golbuu feels intimately connected to the corals he wants to save. During his childhood, the village kids would cut through the mangroves, swim across Nikko Bay, and climb the hill to the Continental Hotel, the first high-class tourist hotel in Palau. “So we’ll go up the dock, run up there, jump in their swimming pool and swim, and then they’ll chase us,” Golbuu says with a chortle, reminiscing. Then they’d jump off the dock and swim back to the village.

Now Golbuu is an ambassador for Palau to the international scientific and conservation communities. He’s full of pride for his country, its natural resources, and its people. Yes, saving the reef is an environmental issue, but he thinks Palauans, considering their traditional ways of life, are sufficiently motivated.

For them, the matter of saving their reefs goes beyond scientific literature and international conservation. They fish there. Palauan women gather sea cucumbers, and exchange carved sea turtle shells as IOUs. They benefit from ecotourism. They grind up coral rocks for building materials or use them to make chemical lime, which many Palauans add to betel nuts before chewing the blood-red mixture to get a mild high. “Sometimes people forget why we’re doing this, and they think that this is for some other people. No, it’s for us,” he says. “This is our island. These are our fish.” And corals and fish go hand in hand.

It’s a complex sort of stewardship Golbuu advocates, a flexible awareness of how resources are shared and how much can be taken. And yet it seems fundamentally Palauan. On a rainy day, I tag along with Golbuu’s employees Uly and Lincoln as they survey the corals and algae growing out on the barrier reef, north of Koror. At one site, while they’re in the water, our Palauan boat driver Ben and I huddle together under a small canopy to stay dry.

Ben was a fisherman for 12 years, but couldn’t take it anymore, he tells me. Catching fish to eat them doesn’t bother him; neither does giving a few to the neighbors in hopes of a good turn later. But he could no longer stomach selling the flesh. Now most days he drives dive boats for tourists. In the last two years of being a fisherman, he felt exhausted. “Every night, I prepare myself for killing,” Ben says. “I didn’t plant that fish.” He repeats himself. “I didn’t plant that fish. The coral made that.”

Map by Alicia DeWitt

Photo credits: LuxTonnerre/Flickr (CC BY) , Joshua Sokol, Klaus Stiefel/Flickr (CC BY-NC) , FGBNMS/Schmahl/NOAA, Aqua Immersion/Flickr (CC BY-NC-ND)

Reporting for this article was made possible by the Taylor/Blakeslee University Fellowship, MIT's Kelly Douglas Fund, the MIT Graduate Program in Science Writing.

Funding for NOVA Next is provided by the Eleanor and Howard Morgan Family Foundation.

National corporate funding for NOVA is provided by Draper. Major funding for NOVA is provided by the David H. Koch Fund for Science, the Corporation for Public Broadcasting, and PBS viewers. Additional funding is provided by the NOVA Science Trust.