CAIRNS, Australia — “I just got a whiff,” said Peter Harrison, a marine scientist, as he leaned over the edge of the boat and pointed his flashlight into the dark water. “It’s really coming through now.”
It was shortly after 10 pm on a cloudy December night, and Harrison, a coral researcher at Australia’s Southern Cross University, was about 25 miles off the coast of northern Queensland. He was with a group of scientists, tourism operators, and Indigenous Australians who had spent the last few nights above the Great Barrier Reef — the largest living structure on the planet — looking for coral spawn.
And apparently, it has a smell.
Over a few nights in the Australian summer, shortly after the full moon, millions of corals across the Great Barrier Reef start bubbling out pearly bundles of sperm and eggs, known as spawn. It’s as if the reef is snowing upside down. Those bundles float to the surface and break apart. If all goes to plan, the eggs of one coral will encounter the sperm of another and grow into free-swimming coral larvae. Those larvae make their way to the reef, where they find a spot to “settle,” like a seed taking root, and then morph into what we know of as coral.
- The Great Barrier Reef, the world’s largest living structure, will likely collapse by the end of the century without immediate and steep cuts to carbon emissions.
- An enormous group of scientists, backed with nearly $300 million, is working tirelessly to delay that decline through an initiative called the Reef Restoration and Adaptation Program.
- At the core of their approach is assisted reproduction — i.e., helping coral have more babies — which they do at sea and in one of the world’s largest research aquariums.
- The broader reef conservation industry in Australia has not fully reckoned with the climate reality it faces, and that undermines efforts to slash emissions, the only long-term solution to save reefs.
Spawning on the Great Barrier Reef has been called the largest reproductive event on Earth, and, in more colorful terms, “the world’s largest orgasm.” Coral spawn can be so abundant in some areas above the reef that it forms large, veiny slicks — as if there had been a chemical spill.
This was what the team was looking for out on the reef, and sniffing is one of the only ways to find it, said Harrison, who was among a small group of scientists who first documented the phenomenon of mass coral spawning in the 1980s. Some people say coral spawn smells like watermelon or fresh cow’s milk. To me it was just vaguely fishy.
“Here we go,” said Mark Gibbs, another scientist onboard and an engineer at the Australian Institute of Marine Science (AIMS), a government agency. All of a sudden the water around us was full of little orbs, as if hundreds of Beanie Babies had been ripped open. “Nets in the water!” Gibbs said to the crew. A few people onboard began skimming the water’s surface with modified pool nets for spawn and then dumping the contents into a large plastic bin.
That night, the team collected hundreds of thousands of coral eggs as part of a Herculean effort to try to keep the Great Barrier Reef alive. Rising global temperatures, together with a raft of other challenges, threaten to destroy this iconic ecosystem — the gem of Australia, a World Heritage site, and one of the main engines of the country’s massive tourism industry. In response to these existential threats, the government launched a project called the Reef Restoration and Adaptation Program (RRAP). The goal is nothing less than to help the world’s greatest coral reef survive climate change. And with nearly $300 million in funding and hundreds of people involved, RRAP is the largest collective effort on Earth ever mounted to protect a reef.
The project involves robots, one of the world’s largest research aquariums, and droves of world-renowned scientists. The scale is unlike anything I’ve ever seen.
But even then, will it be enough?
The first thing to know about the Great Barrier Reef is that it’s utterly enormous. It covers about 133,000 square miles, making it significantly larger than the entire country of Italy. And despite the name, it’s not really one reef but a collection of 3,000 or so individual ones that form a reef archipelago.
Another important detail is that the reef is still spectacular.
Over three days in December, I scuba dived offshore from Port Douglas and Cairns, coastal cities in Queensland that largely run on reef tourism, a whopping $5.3 billion annual industry. Descending onto the reef was like sinking into an alien city. Coral colonies twice my height rose from the seafloor, forming shapes mostly foreign to the terrestrial world. Life burst from every surface.
What really struck me was the color. Two decades of scuba diving had led me to believe that you can only find vivid blues, reds, oranges, and pinks in an artist’s imaginings of coral reefs, like in the scenes of Finding Nemo. But coral colonies on the reefs I saw here were just as vibrant. Some of the colonies of the antler-like staghorn coral were so blue it was as if they had been dipped in paint.
It’s easy to see how the reef — built from the bodies of some 450 species of hard coral — provides a foundation for life in the ocean. While cruising around large colonies of branching coral, I would see groups of young fish hiding out among their nubby calciferous fingers. The Great Barrier Reef is home to more than 1,600 fish species, many of which are a source of food for Indigenous Australians and part of a $200 million commercial fishing industry.
“The reef is part of our life,” said Cindel Keyes, an Indigenous Australian of the Gunggandji peoples, near Cairns, who was part of the crew collecting coral spawn with Harrison. RRAP partners with First Nations peoples, many of whom have relied on the reef for thousands of years and are eager to help sustain it. “It’s there to provide for us, too,” Keyes, who comes from a family of fishers, told me.
The Great Barrier Reef is not dead, as many visitors assume from headlines. But in a matter of decades — by the time the children of today grow old — it very well could be.
The world’s coral reefs face all kinds of problems, from big storms to runoff from commercial farmland, but only one is proving truly existential: marine heat. Each piece of coral is not one animal but a colony of animals, known as polyps, and polyps are sensitive to heat. They get most of their food from a specific type of algae that lives within their tiny bodies. But when ocean temperatures climb too high, polyps eject or otherwise lose those algae, turn bleach-white, and begin to starve. If a coral colony is “bleached” for too long, it will die.
The global prognosis is bleak. The world has already lost about half of its coverage of coral reefs since the 1950s, not including steep losses over the last two decades. And should wealthy countries continue burning fossil fuels — pushing global temperatures more than 2 degrees Celsius above the pre-industrial baseline — it will likely lose the rest of it.
Projections for the Great Barrier Reef are just as grim. A recent study published in the prestigious journal Nature Communications projected that coral cover across the reef would decline, on average, by more than 50 percent over the next 15 years, under all emissions scenarios — including the most optimistic. The reef would only later recover to anything close to what it looks like today, the authors wrote, if there are immediate, near-impossibly steep emissions cuts. (The study was funded by RRAP.)
The reef has already had a taste of this future: In the last decade alone, there have been six mass bleaching events. One of the worst years was 2016, when coral cover across the entire reef declined by an estimated 30 percent. Yet recent years have also been alarming. Surveys by AIMS found that bleaching last year affected a greater portion of the reef than any other year on record, contributing to record annual declines of hard coral in the northern and southern stretches of the reef.
How much coral is left on the Great Barrier Reef?
One hopeful, and rather confusing, detail reported by the Australian Institute of Marine Science is that the portion of reef covered by hard coral is still above the long-term average in the northern and southern parts of the reef. This points to coral’s propensity to grow back and recover from past bleaching. Souring what might otherwise seem like good news is that much of the coral that’s regrown is considered “weedy” — species that quickly take over and dominate the reef after a die-off. These species also tend to be most sensitive to heat stress, cyclones, and a coral-eating pest called the crown-of-thorn starfish. So as they become more common, the reef is likely to become prone to a boom and bust cycle.
“We’ve got immense volatility in coral cover at any given reef,” said Morgan Pratchett, a marine ecologist at James Cook University. “We have reduced the biodiversity on those reefs, and it’s just being driven by weedy species. Now we’re in an era where the existing choral assemblage is so vulnerable to any given disturbance. We’ve undermined the resilience.”
“I’ve been suffering,” said Harrison, who’s been diving on the Great Barrier Reef for more than 40 years. “I’ve got chronic ecological grief. Sometimes it’s overwhelming, like when you see another mass bleaching. It can be quite crushing.”
The problem isn’t just bleaching but that these events are becoming so frequent that coral doesn’t have time to recover, said Mia Hoogenboom, a coral reef ecologist at Australia’s James Cook University, who’s also involved in RRAP.
“The hopeful part is if we can take action now to help the system adapt to the changing environment, then we’ve got a good chance of keeping the resilience in the system,” Hoogenboom said. “But the longer we wait, the less chance we have to maintain the Great Barrier Reef as a functioning ecosystem.”
That night in December, after filling two large plastic bins onboard with coral spawn, the crew motored to a nearby spot on the reef where several inflatable pools were floating on the ocean’s surface. The boat slowly approached one of the pools — which looked a bit like a life raft — and two guys onboard dumped spawn into it.
The government established RRAP in 2018 with an ambitious goal: to identify tools that might help the reef cope with warming, refine them through research and testing, and then scale them up so they can help the reef at large. It is a massive undertaking. RRAP involves more than 300 scientists, engineers, and other experts across 20-plus institutions, including AIMS, which operates one of the world’s largest research aquariums called the National Sea Simulator. And it has a lot of money. The government committed roughly $135 million to the project, and it has another $154 million from private sources, including companies and foundations. It’s operating on the scale of decades, not years, said Cedric Robillot, RRAP’s executive director.
Scientists at RRAP have now honed in on several approaches that they think will work, and a key one is assisted reproduction — essentially, helping corals on the reef have babies. That’s what scientists were doing on the water after dark in December.
Normally, when corals spawn, only a fraction of their eggs get fertilized and grow into baby corals. They might get eaten by fish, for example, or swept out to sea, away from the reef, where the larvae can’t settle. That’s simply nature at work in normal conditions. But as the reef loses more and more of its coral, the eggs of one individual have a harder time meeting the sperm of another, leading to a fertility crisis.
RRAP is trying to improve those odds through what some have called coral IVF.
At sea, scientists skim spawn from the surface and then load them into those protected pools, which are anchored to the reef. Suspended inside the pools are thousands of palm-sized ceramic structures for the larval coral to settle on, like empty pots in a plant nursery. After a week or so, scientists will use those structures — which at that point should be growing baby corals — to reseed damaged parts of the reef.
With this approach, scientists can collect spawn from regions that appear more tolerant to warming and reseed areas where the corals have been killed off by heat. Heat tolerance is, to an extent, rooted in a coral’s DNA and passed down from parent to offspring. So those babies may be less likely to bleach and die. While baby corals are growing in those pools, scientists can also introduce specific kinds of algae — the ones that live symbiotically within polyps — that are more adapted to heat. That may make the coral itself more resistant to warming.
But what’s even more impressive is that scientists are also breeding corals on land, at the National Sea Simulator, to repopulate the reef. SeaSim, located a few hours south of Cairns on the outskirts of Townsville, is essentially a baby factory for coral.
I drove to SeaSim one evening in December with Robillot, a technophile with silver hair and a French accent. He first walked me through a warehouse-like room filled with several deep, rectangular tanks lit by blue light. The light caused bits of coral growing inside them to fluoresce. Other than the sound of running water, it was quiet.
The main event — one of the year’s biggest, for coral nerds anyway — was just outside.
SeaSim has several open-air tanks designed to breed corals with little human intervention. Those tanks, known as autospawners, mimic the conditions on the wild reef, including water temperature and light. So when scientists put adult corals inside them, the colonies will spawn naturally, as they would in the wild. The tanks collect their spawn automatically and mix it together in another container that creates the optimal density of coral sperm for fertilization.
Observing spawning isn’t easy. It typically happens just once a year for each species, and the timing can be unpredictable. But I got lucky: Colonies of a kind of branching coral known as Acropora kenti were set to spawn later that evening. Through glass panels on the side of the autospawners, I saw their orangish branches, bunched together like the base of a broom. They were covered in pink, acne-like bumps — the bundles of spawn they were getting ready to release — which was a clear sign it would happen soon.
As it grew dark, the dozen or so people around the tanks flipped on red headlamps to take a closer look. (White light can disrupt spawning.) Around 7:30 pm, the show started. One colony after another popped out cream-colored balls. They hung for a moment just above the coral branches before floating to the surface and getting sucked into a pipe. It was a reminder that corals, which usually look as inert as rocks, really are alive. “It’s such a beautiful little phenomenon,” Robillot said, as we watched together. “It’s a sign that we still have vitality in the system.”
After spawning at SeaSim, scientists move the embryos into larger, indoor tanks, where they develop into larvae. Those larvae then get transferred to yet other tanks, settling on small tabs of concrete. Scientists then insert those tabs into slots on small ceramic structures — those same structures as the ones suspended in the floating pools at sea — which they’ll use to reseed the reef. One clear advantage of spawning corals in a lab is that scientists can breed individual corals that appear, through testing, to be more resistant to heat. Ideally, their babies will then be a bit more resistant, too.
During spawning late last year, SeaSim produced roughly 19 million coral embryos across three species.
“People often don’t understand the scale that we’re talking about,” said Carly Randall, a biologist at AIMS who works with RRAP. “We have massive numbers of autospawning systems lined up. We have automated image analysis to track survival and growth. It is like an industrial production facility.”
Including the spawn collection at sea, RRAP produced more than 35 million coral embryos last year that are now growing across tens of thousands of ceramic structures that will be dropped onto the reef. The goal RRAP is working toward, Robillot says, is to be able to stock the reef with 100 million corals every year that survive until they’re at least 1 year old. (Under the right conditions, each ceramic structure can produce one coral that lives until 1 year old in the ocean, Robillot told me. That means RRAP would need to release at least a million of those structures on the reef every year.)
On that scale, the project could help maintain at least some coral cover across the reef, even in the face of more than 2 degrees C of warming, Robillot said, citing unpublished research. One study, published in 2021 and partially funded by RRAP, suggests that a combination of interventions, including adding heat-tolerant corals, can delay the reef’s decline by several years.
“We are not replacing reefs,” Robillot said. “It’s just too big. We’re talking about starting to change the makeup of the population by adapting them to warmer temperatures and helping their recovery. If you systematically introduce corals that are more heat-tolerant over a period of 10 to 20 to 30 years, then over a hundred years, you significantly change the outlook for your population.”
The obvious deficiency of RRAP, and many other reef conservation projects, is that it doesn’t tackle the root problem: rising greenhouse gas emissions. While restoration might help maintain some version of coral reefs in the near term, those gains will only be temporary if the world doesn’t immediately rein in carbon emissions. “It all relies on the premise that the world will get its act together on emissions reductions,” Robillot said. “If we don’t do that, then there’s no point, because it’s a runaway train.”
Many groups involved in reef conservation have failed to reckon with this reality, even though they’re often on the front lines of climate change. During my trip, I would be on dive boats listening to biologists talk about restoration, while we burned diesel fuel and were served red meat — one of the most emissions-intensive foods. A lot of tour operators, some of whom work with RRAP, don’t talk about climate change much at all. Two of the guides who took me out on the reef even downplayed the threat of climate change to me.
Yolanda Waters, founder and CEO of Divers for Climate, a nonprofit network of scuba divers who care about climate change, said this isn’t surprising. “At the industry level, climate change is still very hush-hush,” said Waters, who previously worked in the reef tourism industry. “In most of those boats, climate messaging is just nonexistent.”
This makes some sense. Tourism companies don’t want people to think the reef is dying. “When international headlines describe the Reef as ‘dying’ or ‘lost,’ it can create the impression that the visitor experience is no longer worthwhile, even though large parts of the Reef remain vibrant, actively managed, and accessible,” Gareth Phillips, CEO of the Association of Marine Park Tourism Operators, a trade group, told me by email. (I asked around, but no one could point me to data that clearly linked negative media stories to a drop in visitors to the Great Barrier Reef.)
Yet by failing to talk about the urgent threat of climate change, the tourism industry — a powerful force in Australia, that influences people from all over the world — is squandering an opportunity to educate the public about what is ultimately the only way to save the reef, said Tanya Murphy, a campaigner at the Australian Marine Conservation Society, a nonprofit advocacy group. Tourists are ending their vacation with the memory of, say, a shark or manta ray, not a new urge to fight against climate change, Waters said. So the status quo persists: People don’t connect reducing emissions with saving the reef, even though that’s “the only reef conservation action that can really be taken from anywhere,” she added.
(Not everyone in the tourism industry is so quiet. Eric Fisher, who works for a large Australian tourism company called Experience Co Limited, says he tells tourists that climate change is the biggest threat to the Great Barrier Reef. “It’s what we tell people every day,” Fisher told me. “So as they fall in love with it, they’re more likely to leave with an understanding of that connection.”)
Keeping mum on climate change, while speaking loudly about restoration and other conservation efforts, including RRAP, can also take pressure off big polluters to address their carbon footprints, Waters and Murphy said. Polluters who fund reef conservation, including the government and energy companies, are given social license to operate without stricter emissions cuts, because the public thinks they’re doing enough, they said.
In reality, the Australian government continues to permit fossil fuel projects. Last year, for example, the Albanese administration, which is politically left of center, approved an extension of a gas project in Western Australia that Murphy and other advocates call “a big carbon bomb.” The extension of the project, known as the North West Shelf, will produce carbon emissions equivalent to about 20 percent of Australia’s current yearly carbon footprint, according to The Guardian.
A spokesperson for the Albanese government acknowledged in a statement to Vox that climate change is the biggest threat to coral reefs globally. “It underlines the need for Australia and the world to take urgent action, including reaching net zero emissions,” the statement, sent by Sarah Anderson, said. “The Albanese Government remains committed to action on climate change and our net zero targets.”
Anderson highlighted a government policy called the Safeguard Mechanism, which sets emissions limits for the country’s largest polluters, including the North West Shelf Facility. Yet the policy only applies to Scope 1 emissions. That means it doesn’t limit emissions tied to gas that the North West Shelf project exports — the bulk of the project’s carbon footprint.
Although Australia has far fewer emissions compared to large economies like the US and China, the country is among the dirtiest on a per-capita basis. If any country can reduce its emissions, it should be Australia, Waters said. “We’re such a wealthy, privileged country,” Waters said. “We’ve got the biggest reef in the world. If we can do better, why wouldn’t we?”
On a stormy morning, near the end of my trip, we returned to the reef — this time, visiting another set of floating pools, offshore from Port Douglas. They had been filled with spawn several days earlier. Small corals were now growing on the ceramic structures, and they were ready to be deployed on the reef.
After a nauseating two-hour ride out to sea, a group of scientists and tourism operators jumped into small tenders and collected the structures from inside the pools. Then they motored around an area of the reef that had previously been damaged by a cyclone and started dropping coral babies off the side of the boat, one by one.
As it started to pour, and I noticed water flooding into the front of the tender, I couldn’t help but think about how absurd all of this was. Custom-made pools and ceramics. Hours and hours on the reef, floating in small boats in a vast ocean. Sniffing out spawn.
“You sort of think about the level of effort, that we’re going to try and rescue something that’s been on our planet for so many millions of years,” Harrison told me on the boat a few nights earlier. “It seems a bit ironic that humans now have to intervene to try and rescue corals.”
RRAP is making this process far more efficient, Robillot says — machines, not people, will eventually be dropping the ceramic structures off the boats, for example. But still, why not invest the money instead in climate advocacy or clean energy? Isn’t that an easier, perhaps better, way to help?
It can’t be either or, Robillot said. And it’s not, he contends. Many donors who fund the Great Barrier Reef Foundation, a core RRAP partner and Robillot’s employer, are putting more of their money into climate action relative to reef conservation, he said. The government of Australia, meanwhile, says it’s spending billions on clean energy and green-lit a record number of renewable energy projects in 2025. Plus, while the scale of resources behind RRAP is certainly huge for coral reefs, it’s tiny compared to the cost of fixing the climate crisis. “We need trillions,” Robillot said.
Investing that roughly $300 million into fighting climate change could have a small impact on reefs decades from now. Putting it into projects like RRAP helps reefs today. It’s only a waste of money — worse than a waste of money — if that investment undermines climate action. And Robillot doesn’t think it does.
The Great Barrier Reef Foundation has been criticized for its ties to mining and energy companies, including Peabody Energy and BHP. The Reef Foundation currently receives money from mining giant Rio Tinto and BHP Foundation (which is funded by BHP) for projects unrelated to RRAP, the organization told Vox. “It is a bit concerning,” Murphy told me. “It’s really important that we get polluters to pay for the damage they’re causing. But that should be done as an obligatory tax and they should not be getting any marketing benefits from that.”
Robillot argues that these companies have not influenced RRAP’s work, or restricted what its staff can say about climate change. “If we can still scream that climate change is the main driver of loss of coral reefs, I don’t have an issue,” he said. “I don’t think it’s realistic to only take money from people who do not have any impact on climate change. I don’t know anyone.”
Yet if there’s one argument that I find most convincing for RRAP — for any project trying to help wildlife suffering from climate change — it’s that even if the world stops burning fossil fuels, these ecosystems will still decline. They will still need our support, our help to recover. The planet is currently crossing the 1.5-degree threshold, at which point the majority of coral reefs worldwide are expected to die off. “If you stop emissions today, they will still suffer,” Robillot said of reefs. “And we’re not going to stop emissions today.”
So much of reef conservation is absurd. We shouldn’t need to collect coral spunk from the open ocean in the middle of the night or breed these animals in tanks on land. Then again, these sorts of efforts are what scientists, Indigenous Australians, and the most thoughtful divers can do — what they are doing — to help the reef today.
“There’s so much work happening on the ground,” Waters, of Divers for Climate, told me. “All of those scientists, all of those [tourism] operators, are genuinely doing everything they can. It would be great for the Australian government to go, ‘Well, this is what we can do for reefs, too,’ pick up their game on climate, and show that we’re actually in it together.”
