An exclusive look inside the largest effort ever mounted to keep the Great Barrier Reef alive
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.
Key takeaways
- 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 (https://blog.padi.com/the-great-barrier-reef-coral-spawning-the-worlds-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 (https://wttc.org/news/australias-travel-tourism-sector-set-to-reach-record-315bn-in-2025) . 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 (https://barrierreef.org/uploads/GBRValue-FullReport-Oct25.pdf) , 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 (https://www2.gbrmpa.gov.au/learn/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 (https://www2.gbrmpa.gov.au/access/zoning/commercial-fishing-and-zoning) .
"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 (https://gbrrestoration.org/rrap-about-us/traditional-owners-and-indigenous-partnerships/) , 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 (https://www.nationalgeographic.com/magazine/article/explore-atlas-great-barrier-reef-coral-bleaching-map-climate-change) . 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 (https://www.cell.com/one-earth/fulltext/S2590-3322(21)00474-7) of its coverage of coral reefs since the 1950s, not including steep losses over the last two decades (https://www.vox.com/climate/23868423/florida-coral-reef-bleaching-heat-wave-climate-change) . 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 (https://www.vox.com/climate/24137250/coral-reefs-bleaching-climate-change) .
Projections for the Great Barrier Reef are just as grim. A recent study published (https://www.nature.com/articles/s41467-025-65015-4) 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 (https://www.nature.com/articles/s41586-018-0041-2) . Yet recent years have also been alarming. Surveys by (https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2024-25) 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 (https://www.vox.com/down-to-earth/395569/florida-coral-reef-climate-change-baby-problem) .
RRAP is trying to improve those odds through what some have called coral IVF (https://www.barrierreef.org/news/explainers/what-is-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 (https://www.sciencedirect.com/science/article/pii/S0966842X24001392) 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
