Headlines have portrayed Australia’s bucket-list destination as dead, or dying. But that’s an oversimplification of a complex story—and the most dire threat from tourism may be what you least expect.

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Page 53 of my dive log from 1992 contains the details of my 26th scuba dive. For location, I wrote: “study site, Davies Reef, GBR.” Under purpose: “Acanthaster fert expt.” At the time, I was a 25-year-old graduate student in marine science at the University of Southern California. I had a berth on a research cruise organized by the Australian Institute of Marine Science to the Great Barrier Reef near Townsville, about midway along its latitudinal expanse. The project’s aim was to understand the population explosion of the sea star Acanthaster planci. These prickly echinoderms have the common name crown of thorns starfish, often shortened to COTS. Since the 1960s, swarms of COTS have intermittently infested the Reef, eating coral with the voraciousness of locusts on crops. They were—and still are—among the greatest threats to the coral. Half of the Reef bears scars from COTS outbreaks. On dive #26, my job was to scan for COTS, collect them with massive barbecue tongs to avoid getting poked, and return them to the research boat for study. We induced spawning and collected the eggs in a modified giant syringe called a COTSucker. A single female, it would turn out, produces 35 million eggs a year. That kind of fertility is why population control has proven difficult. My search target was about the size of a dinner plate, rust- or purple-colored with 8 to 21 arms arrayed around a central disk like petals of a sunflower. During the day, COTS hide in dark crannies. Peeking into those shadows, I met nervous cardinal fish and spider-like feather stars. Sparkling clouds of blue chromis tucked themselves into the arms of branching corals. The pastel lips of giant clams kissed closed as I kicked past. Crossing the top of one minivan-sized coral cluster, I had the urge to look forward rather than down. I stopped short in the water, flaring my dive fins out, penguin-style. I was face-to-face with a person-sized, black-tipped reef shark. Our eyes locked. My body shook involuntarily, a ripple that began at my head and cascaded down to my feet. The shark shook, too, beginning at its head and ending at its tail. As if reaching the same conclusion simultaneously, we turned in opposite directions, and swam away from each other. Though I would complete 14 dives over the week, encountering dozens of COTS, this moment is the one that sticks with me, certainly because it was the only time I have ever come face-to-face with a shark. But even more, it taught me a key truth about the Great Barrier Reef: When you are looking for one thing, you are just as likely to discover something even more powerful. Photo by Pablo Cogollos Vibrancy is still visible on the Reef. A Natural Wonder In the past few years, perhaps you've seen them—headlines proclaiming that it’s your last chance to see the Reef, that all that’s left to do is write the Reef’s obituary. These broad strokes are not only misleading but also an oversimplification of just how huge and complicated the Great Barrier Reef really is. A UNESCO World Heritage site and one of the seven wonders of the natural world, the Great Barrier Reef stretches 1,400 miles across 14 degrees of latitude. You could cover the entire West Coast of the United States with its length, and bits would drip off the edges into Canada and Mexico. Some 13,000 years ago, the Reef’s 600 continental islands formed when sea levels rose, submerging a coastal mountain range. Later, life added its own touches with 150 mangrove islands, 300 coral islands called cays, and 3,000 submerged reefs. Diversity on the Reef is abundant. The 600 species of hard and soft coral are the centerpiece, but just the start. Besides the black-tipped reef shark, 132 other shark species live on the Reef along with 1,625 species of fish. Six of the world’s seven species of sea turtles glide through its waters, and four of them lay their eggs in its islands’ sandy beaches. Dugong, a relative of manatees; busy bottlenose dolphins; massive humpback whales; and dwarf minke whales are among the 30 species of marine mammals sounding their haunting calls through the waves. These, all without including the thousands of species of urchins, sea cucumbers, lobster, crab, shrimp, marine spiders, clams, scallops, sea anemones, sea pens, jellyfish, sponges, and worms. Not to mention thousands of other members of marine phyla so fantastic and unfamiliar—like bryozoans, ascidians, and tunicates—that you might want to take a moment to Google them. “Scarce a flower upon earth can vie in brilliance of tint with many of the anemones of the oceans, while the birds of the tropics find their plumage dulled besides the remarkable fishes which are found in these coasts.” For more than 50,000 years, the Aboriginal and Torres Strait Islander people made their homes along the Great Barrier Reef, traveling among its islands in canoes and fishing among its reefs. They are its Traditional Owners, whose history and spirituality are intertwined with extensive knowledge of the marine world. Australians familiar with the Reef refer to coral clusters like the one I swam over when I met the shark as “bommies.” The word owes its roots to the indigenous term “bombora,” which means large rock. Despite its astonishing biological richness, tourists were slow to find the Great Barrier Reef. In 1893, that changed: After four years of exploration, British naturalist William Saville-Kent published The Great Barrier Reef of Australia; Its Products and Potentialities, with photographs and color illustrations of underwater life. The book was a hit, receiving rave reviews in scientific journals like Nature and effusive descriptions in daily newspapers like the Cambridge Review, which wrote, “Scarce a flower upon earth can vie in brilliance of tint with many of the anemones of the oceans, while the birds of the tropics find their plumage dulled besides the remarkable fishes which are found in these coasts.”

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Yet even as Saville-Kent publicized the Reef’s natural beauty, he highlighted the extractive potential of lucrative pearl oyster beds and fisheries. “The latent resources of Queensland’s—or in its restricted sense, the Barrier’s—marvellous [sic] fish-fauna,” he wrote, “present almost unlimited possibilities of profitable development.” This tension between human impact and protection defines the complicated relationship we humans have with the Reef—one that continues today. Photos by Shutterstock A clownfish in anemone (L) and a hawksbill turtle (R). The Shark Shift Although I was grateful for the spot on the research cruise on Davies Reef in 1992, I hadn’t really come to Australia to study COTS. I had come to see one of the world’s greatest marvels. In October and November, just after the full moon, the multitudes of corals on the Reef release their spawn in synchrony. Small, round, pinkish eggs bob upward like confetti caught in a realm of reverse gravity. It’s unbidden moments of wonder like those that made my visit so powerful. Every year, 2.26 million visitors come to the Great Barrier Reef to chase that magic. Some come to dive and experience its natural wonders up close, others to peer at its complex beauty through glass-bottomed boats or out the windows of semi-submersibles or from high above in scenic flights. In all, tourism on the Great Barrier Reef supports 64,000 jobs—more than Qantas (Australia’s flag carrier) or Telstra (Australia’s largest mobile network), according to a 2017 Deloitte Access Economics Report. The Great Barrier Reef contributes more than $6.4 billion to the Australian economy annually, and it is valued at $56 billion thanks to its economic, social, and iconic clout. “Tourism does comparatively little direct damage to the Reef." Despite early concerns from Australian residents that tourism was a great threat to the Great Barrier Reef, these apprehensions have been largely unfounded, thanks to a tightly controlled system of who visits the Reef and when. Still, misconceptions abound. Eric Fisher has spent more than 15 years working in tourism on the Reef, most recently developing the marine science and education program GBR Biology with the adventure tourism company Experience Co. in Cairns. When I asked him about the negative effects of travelers on the Reef, I was expecting rightful complaints about litter and garbage, dropped anchors, and wayward divers’ fins. But Fisher did what the shark had done so many years ago: shifted my attention to something that was right in front of me. “Tourism does comparatively little direct damage to the Reef,” he says, pointing out that most operators with permits to do business on the Reef insist on good etiquette and go above and beyond the rules. Instead, the most dire threat is something more big-picture—fitting, for such a big-picture place. “The greatest damage from tourists is their carbon footprint,” he says. Courtesy of Tourism and Events Queensland The Pixies Garden on the Great Barrier Reef is a popular spot for divers. A Warming Planet Consider how far the Australian continent is from others, and Fisher’s caveat is sobering: In 2018, Australia’s top international visitors by country were China (1.43 million), New Zealand (1.38 million), the United States (789,000), and the United Kingdom (733,000). Couple that with the knowledge that a single one-way ticket in economy class from Beijing to Sydney generates 1.45 tons of carbon dioxide as pollution, and the amount of trash left behind by tourists seems, in comparison, like less of a big deal. As our planet warms due to the accumulation of atmospheric carbon emissions, the oceans absorb a disproportionate amount of heat; since 1955, they have taken in more than 90 percent of this excess heat, raising global average seawater temperatures almost 2 degrees Fahrenheit. Coral are particularly sensitive to temperature. Though they are animals like us, they have symbiotic algae embedded in their tissues, akin to photosynthetic tattoos. When the water warms by a few degrees for a few weeks, the algae abandon the coral, depleting the reefs of their color, a process called bleaching. Deprived of energy supplies, the coral then begin to starve. If the warmer temperatures persist, they die. Related Rewilding Australia In 2016, the Great Barrier Reef experienced a major bleaching event, severely affecting the north. With barely time to recover, the Reef underwent another major bleaching in 2017, this time levying most of the damage at its midsection. In the course of two years, half the coral on the Reef had died. (In the next decades, fast-growing branching corals could fill the reef’s empty spots, but scientists worry about the impact of shifting architecture and community structure on the health of the reefs.) This February, as the Southern Hemisphere summer intensified, the seas along the Great Barrier Reef experienced their warmest temperatures since 1990. Coral Reef Watch, a program of the National Oceanographic and Atmospheric Administration, issued maps marked in the deep red of the highest alert level, in which “severe bleaching and significant mortality are likely.” But a map bathed in red does a disservice to the complexity of the Great Barrier Reef, Fisher pointed out. Coral colonies consist of pencil eraser–sized individuals known as polyps, which are similar to sea anemones. On a single coral, 80 percent of the polyps might bleach, but 20 percent will remain healthy, or the other way around. And then there’s the scalability: Coral colonies may have hundreds or thousands of polyps, and reefs might contain thousands or tens of thousands of colonies. The Great Barrier Reef, as a whole, contains thousands of reefs. Viewed that way, the Reef is trillions of individual responses. “From that polyp level, right up to the reef level, and then the region level, that’s this whole patchiness story,” says Fisher. “It’s the hardest story to tell.” Courtesy of Great Barrier Reef Marine Park Authority Master Reef Guides on a hike near the Great Barrier Reef. “A Hundred New Questions” In 1985, inspired by a National Geographic article about the Reef’s new status as a UNESCO World Heritage site, Fiona Merida’s father packed up the family in their brown Nissan and drove 2,000 miles from their home in Melbourne to the coast. Once there, Fiona’s father showed her how to wear a snorkel mask for the first time. “I looked down [in the water] and saw the most amazing thing I’d ever seen—a busy underwater city with lots of interesting faces and bizarre shapes, all going about their business,” she says.