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At the Great Barrier Reef
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Great Barrier Reef

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By Douglas H. Chadwick Photographs by David Doubilet

Largest structure on the planet built by living organisms, Australia’s coral rampart hosts a carnival of sea life.

Sometimes at its outer edge and sometimes closer, the beam from the flashlight kept reflecting off big cat eyes. They glimmered pale silver, with pupils darker than the darkness through which they glided. But cats don’t patrol 40 feet (12 meters) deep in the Coral Sea. These were sharks. It was hard to tell what kind they were, but some of the shadowy bodies looked a lot longer than mine.

I breathed up my scuba tank’s air sooner than planned and had to surface far from the boat. Then I was swimming through black swells toward the ship’s distant light as though mired in one of those dreams where you need to move faster but can’t. I promised myself that it would be a while before my next night dive on Australia’s Great Barrier Reef. Yet within days I was beneath a full moon and 50 feet (15 meters) of water looking at more cat eyes.

These belonged to an epaulette shark, small and lovely and speckled, lithe as an eel as it curled round a coral pillar. Two lionfish with fins like flared wing feathers cruised upside down beneath a coral table as though that were the seafloor. Above them a pinnacle of coral twisted nearly to the surface, lit from behind by the ship’s lamps and the moon.

Silhouetted, each shelf, frond, curlicue, and fan emphasized the eerie configurations that develop in the near absence of gravity. Drifting weightless beside them seemed like sightseeing on another planet. But the moment I thought that, I realized that I had it wrong. This scene was the very essence of our home planet, which is, after all, ocean blue. A single coral wall holds a broader representation of earthly life—species from more phyla, or major groups—than an entire continent does. It seems otherworldly only to those of us born above tide line.

Coral reefs form when colonies of tropical marine plants and animals with limestone skeletons rise atop earlier generations. They fashion the most visually diverse natural environments a human can experience, and the Great Barrier Reef is the world’s single largest coral domain. With the broad, shallow continental shelf of tropical northeastern Australia providing an ideal pedestal for growth, this coral complex reaches as far as 160 miles (260 kilometers) offshore and more than 1,250 miles (2,000 kilometers) from north to south. The Great Barrier Reef covers 135,000 square miles (350,000 square kilometers), an expanse greater than Poland.

To explore what amounts to an offshore nation, photographer David Doubilet and I roamed 4,000 miles (6,400 kilometers) on dive boats. We spent so many hours submerged that I began to think land looked weird. The day I found the same sort of remora fish that clings to sharks and manta rays hitching a ride on my leg, I wondered if it might not be time to dry out.

Although the name suggests a continuous strip, the Great Barrier Reef is actually a commonwealth of at least 2,800 reefs. Only some are true barrier reefs—breakwaters rising near the edge of the continental shelf. In the calmer seas behind that cordon, more reefs appear as irregular circles and crescents known as platform reefs. Smaller formations, called patch reefs, are scattered throughout shallow areas.

Fringing reefs grow outward from the mainland’s shores, but more often they are found surrounding the region’s 618 continental, or high, islands, which were mountains and hills along Australia’s Ice Age coast before the glaciers melted and raised sea levels; the Aborigines’ legends of ancient generations walking out to those islands are true. In addition there are about 300 low islands, or cays, formed atop coral shoals from reef sediments. As seabird droppings glue the grains together and colonizing plants build soil, some of those desert isles transform into shadowy woodlands, while storms pound others back into shifting piles of sand.
By acting as a buffer against heavy seas, the reef-and-island complex makes possible neighboring sea grass beds and coastal mangrove forests. Those in turn trap sediments, store nutrients, and serve as nurseries for a number of reef residents. Now add the soft sea bottoms between reefs plus submarine hillocks made entirely of Halimeda, a calcium-hardened green algae.

Put all these habitats together with clear azure waters flowing from the Coral Sea and brown, soil-laden waters washing off the continent. Mix with currents, daily tides, and seasonal weather patterns. What you have is the formula for the Great Barrier Reef ecosystem and lifetimes of discovery.

The better we came to know this offshore nation, the more it resembled a long chain of provinces. Four major sections are widely recognized: Mackay/Capricorn in the south, where the water first warms enough to encourage coral growth, Central, Cairns, and Far Northern, which is the most remote and, being closest to the Equator, hosts the lushest array of life.

Our first destination was the Eastern Fields, a rarely visited atoll that lies outside the Far Northern section near the Gulf of Papua, 200 miles (320 kilometers) east of Australia’s Cape York Peninsula and approaching New Guinea. This pristine marine wilderness represents a part of the Pacific that seeded the continental shelf with coral some 20 million years ago, after Australia drifted north into the tropics.

While I strapped on an air tank, Duncan Johnstone, one of the professional divers helping to crew our boat, offered advice. The waters, he said, would be very clear, with visibility at 150 feet (45 meters) or more, and very shacky, “shack” being how Aussies say “shark.” What kind? “Whalers,” another name for members of the requiem shark family. Great whites are rare in tropical waters. Another big boy is not: the tiger shark, a whaler that grows to 20 feet (6 meters). But Johnstone was referring to the more common five- to ten-foot-long (1.5- to three-meter-long) bronze whalers, gray reef sharks, and silvertips.

“They hunt in small packs,” he continued, “and they like to come right up for a look, give you a bit of a squeeze. Just back toward the reef if you can. Don’t go popping to the surface.”

Descending past green coral that looked like sunken organ pipes, I got squeezed by a pack right away. The whalers moved on, and I leveled out a hundred feet (30 meters) down on the lip of a sheer drop. I hovered awhile, then kicked out into nothing but blueness. Though my depth gauge gave a constant reading, I couldn’t shake the perception of falling. Southern bluefin tuna cruised under my feet. Schooling unicornfish and trevallies, or jacks, swirled past like currents made visible. Far bigger shapes bulked where the blue turned to gloom.

Feeling more and more like a hapless mote of plankton, I turned back and drifted up balcony-like tiers of coral toward the clerestory light far above through chromis,
sergeants, triggerfish, surgeonfish, and clouds of other fish feeding on everything from algae to shrimps to the corals that housed them. By the time I neared the anchor line, I knew the main challenge ahead wasn’t going to be sharks. It was going to be how to make sense of the poly¬chrome dazzle of creation that is a reef.

Heaving aboard after a dive, I would head straight for the identification books, thinking: Surely I can pick out the rainbow fish with pink stripes radiating from its eyes. Aha, it’s a wrasse. But there must be a hundred wrasses here—and at least a dozen with that eye pattern. So is it the tailspot, threespot, checkerboard, pinkbelly, moon, or sunset wrasse?

With new fish species found in the Great Barrier area every year, the total is approaching 2,000. It will likely keep rising. So will the estimates of 4,000 mollusks and at least 350 hard, or reef-building, corals. Researchers counted more than 250 types of shrimps on the reefs just around Heron Island, near the Great Barrier’s southern end. One volleyball-size coral chunk there yielded 1,441 worms from 103 species.

Perhaps for want of enough names to go around, many of the fish I swam with had labels borrowed from land animals: lizardfish, batfish, hogfish, and that double steal, the foxface rabbitfish. Getting better at recognizing species only made me more curious to know why there were so many kinds in the first place. What drives this extravagance of color and form? And how is such biological wealth even possible when the clear, blue quality of tropical seas reflects a scarcity of nutrients and plankton, the base of the food pyramid?

The northern reefs form a nearly continuous ribbon for about 400 miles (640 kilometers). Near the Olinda Entrance, a narrow break in the bulwark, I kayaked across the wave-beaten reef flat behind a coral slope, then dropped overboard with snorkel gear. Dark shapes shot across the bottom ten feet (three meters) below. I tried to follow before I realized that the water was so transparent that I was chasing the shadows of brown boobies flying overhead, carrying fish to the fluffy white chicks waiting on a nearby cay. When I looked down again, I noticed some seaweed tumbling in the current. Then the lacy brown clump hung a left, circled a piece of coral rubble, and darted after a speck of food.
Pretty good for algae, or rather for a juvenile rockmover wrasse that looks and acts like drifting debris, right down to rolling from side to side, presumably to fool predators. Another juvenile has the same flip-flop swimming style, and one is thought to mimic a foul-tasting flatworm for the same purpose. The fact that the adult fish may have different patterns of fins, color, and behavior was my first clue to the puzzle of the diversity around me.

Near the Portlock Reefs I couldn’t figure out the dots moving behind a crack in a coral ridge. My diving partner did, seeing the toothy end of a six-foot-long (1.8-meter-long) black-spotted moray eel emerge to inspect my head from behind. By then I was distracted by a gold-and-white juvenile bicolor parrotfish. As adults, females are reddish brown and males are jade-and-pink. Thus the animal comes in three distinct models. Other fish produce half a dozen—a stronger clue as to how scores of species around a coral knoll can look like hundreds.

A broad spectrum of reef fish switch sex as they age or as changes in the social environment trigger hormones that promote male characteristics at the expense of female traits or vice versa. When the male fairy basslet attending a harem disappears, the dominant female may start acting like a male within hours and become one physically within a few days.

Temporary color changes add to the complexities of sorting out who’s who on the Great Barrier. I watched a brown trumpetfish swim behind a slow-moving star puffer and match its gray tones while using the big blowfish for concealment to sneak up on prey.

I lay on the deck and was just dozing off when it came to me. Not enlightenment, but another fish—splat on my eye. No trouble identifying this one: a flying fish that was soaring away from a pursuer on long, winglike pectoral fins. Tiny squid and baitfish were always jetting onto the stern steps. When Johnstone was filleting a coral trout there for dinner, a bronze whaler surged up onto the transom and thrashed around, trying its damnedest to help carve the meat. Boobies, noddies, and terns perched and pooped all over the bow. We seemed to be joining the ecosystem. No other boat had come into sight for hundreds of miles. Perfect. Just us and the sea.

Part of the pleasure of these unspoiled surroundings came from knowing that Australia was managing them to stay that way. In 1975 virtually the whole offshore nation was declared Great Barrier Reef Marine Park, one of the world’s first national marine sanctuaries and still the biggest. Intended mainly to prevent oil drilling and mining on the reef, the park remains open to many other uses. Commercial fishing, sportfishing, spearfishing, and the collecting of aquarium fish and shells are regulated, however, and some segments are set aside as no-take zones, research zones, or special reserves for troubled species such as dugongs, marine mammals closely related to manatees.

Of the globe’s seven species of sea turtles, six are found in the Great Barrier region. The least imperiled is the flatback, which keeps to Australian waters. Female green turtles travel 1,600 miles (2,575 kilometers) from places like Indonesia and New Caledonia to lay their eggs in spots such as Raine Island, a northern cay. From the boat we watched thousands transform the beach nightly with flailing flippers and flying sand, scattering the seabirds that also come to nest.

Many of the Great Barrier islands are overseen by the Queensland Parks and Wildlife Service, which does much of the day-to-day work of supervising the marine park as well. Raine Island, where Aborigines once came in outrigger canoes to gather food, is now off-limits to most visitors to protect the nesting wildlife, but we were free to swim along the coral slopes it rests upon.
Turtles would pass so close we could make out marks from shark teeth on their shells and chunks missing from limbs. More of the 200- to 400-pound (90- to 180-kilogram) reptiles rested until nightfall in caves on the reef wall. I never peered into one of those dark nooks without also seeing the big eyes of cardinalfish, squirrelfish, or other nocturnal species looking back—yet another clue to the area’s extraordinary biological wealth.

Coral reefs are riddled with caverns and crevices—a microtopography that greatly multiplies both the total surface area and the variety of niches available. This is where the night shift spends the day, the day shift hides at night, and an assortment of sea squirts, soft corals, and sponges, which lack rigid skeletons, makes a full-time home. Tighter crannies take the place of shells, spines, or foul-tasting chemicals as protection for other creatures. Many, including some algae and sponges that look too soft for the job, bore tunnels of their own.

Continuing southward through the Far Northern section, we finally drew near enough to land to see Cape Weymouth on the horizon, then reconnoitered underwater for hours by Ferguson Reef. I sank down to rest on a sand patch, discovered I was maybe a dozen feet (3.7 meters) from a whitetip reef shark doing the same thing, and finger-walked over to a wider sand slope. The shark never budged, but within a minute the barren-looking habitat had scores of garden eels growing out of it, emerging from burrows as the shock of my arrival wore off.
Bumphead parrotfish seemed awfully fond of the place as well. Largest of the region’s 29 parrotfish species, a bumphead can weigh more than a hundred pounds (45 kilograms) and devour five tons (five metric tons) of coral a year. After gouging out chunks with teeth fused into a beak, it chews them with a second set of powerful jaws deep in the throat. As the fish defecated, a curtain of coral slurry descended upon me, and I tried to keep in mind the fact that many a perfect coral sand beach comes from parrotfish dung.

Stay down long enough and even tropical seas drain your body heat. To warm up, all I had to do was rise toward the surface, stoked to bathtub temperature by the sun. When I floated over sand at this upper level, the brightness made my eyes ache. The driving force behind the abundance of reef life was becoming hard to miss: limitless solar power. Just as on land, the marine food chain rests upon the ability of plants to convert solar energy to food and building materials. The secret to the fecundity of the Great Barrier is that so many of the plants dwell inside animals.

Mistaken for colorful plants themselves at one time, corals are actually carnivores related to anemones and jellyfish. Like them, corals use tentacles with stinging cells to snare microscopic prey. Corals can also catch food on their mucous coating and absorb nutrients directly through their epidermis. Even so, as much as 90 percent of their nourishment comes from golden brown algae they host in their tissues at a density of millions per square inch (millions per square centimeter). The corals’ enzymes cause the algae to leak carbohydrates. In return the algae get nitrogen from the corals’ waste material, along with a home.

About 90 percent of giant clams’ food comes from the same symbiotic algae. The clams grow these microscopic plants beneath translucent panels, essentially farming them inside a fleshy greenhouse. A surprising number of other animals nurture internal algae too, from sponges to thin-skinned flatworms.

Partnerships play a role almost anywhere you look on a reef. The largest marine fish family is that of gobies, with more than 2,000 species worldwide. Many of the known tropical species share burrows with shrimps, which keep the holes clean while the gobies act as sentinels, warning of danger. Not that the laws of tooth and maw have been repealed. During one dive I saw a diagonal-banded sweetlips open wide to have parasites removed from its mouth and gills by what looked like a cleaner wrasse. Instead a fang-toothed blenny, an accomplished mimic of the cleaner wrasse, bit off a hunk of the sweetlips’s inner cheek and skedaddled. Close by, a big barracuda yawned to accommodate a true cleaner wrasse—then snapped its teeth shut and gulped the thing.
Roughly 175 miles (280 kilometers) south of Ferguson Reef we crossed into the Cairns section, where the Great Barrier generally runs nearest the mainland, and stepped onto Lizard Island after three weeks at sea. The ground seemed to sway so much I could hardly stand. Still, the prospect of walking for more than the 72-foot (22-meter) length of our boat was so exhilarating that I staggered all the way to Cook’s Look, the island’s granite summit, 1,178 feet (359 meters) above sea level.

In 1770, during a voyage to find the rumored continent of Terra Australis, Capt. James Cook of England scrambled up to search for a way out of what he had begun to view as an endless barricade of reefs. The great navigator had already holed the hull on the coral once. By 1900 the Great Barrier had claimed 1,200 vessels. We had made a few edgy excursions ourselves through portions still marked “Unsurveyed.”

During my visit Cook’s Look was wrapped in glowing clouds. Torresian imperial pigeons called from eucalyptus trees, and four-foot (1.2-meter) monitor lizards rustled in the leaves underneath. The place spoke less of the European era than of Dreamtime, the mystical age envisioned by Aborigines who once held initiation rites for young men atop the peak.

Hiking on to the Lizard Island Research Station, I tracked down Bob Podolsky, a marine biologist visiting from the University of North Carolina at Chapel Hill. He had come to study brittle stars, so named because their long arms break off easily. While a detached arm coils and squirms, distracting whatever grabbed it, the rest of the brittle star can escape, soon to regrow the missing limb.

Podolsky focused a microscope on a larva hatched from a minuscule brittle star egg. An eater of algae, this nearly invisible plankton particle looked nothing like the adult—or anything else, except maybe avant-garde jewelry or an interstellar probe. I was remembering why my first childhood glimpse of the animated cosmos within a water droplet hooked me on biology forever when Podolsky said, “An adult brittle star puts out more than a million larvae in its lifetime and yet will replace itself with just a single offspring if it’s lucky. So the chance of a larva surviving is literally one in a million.”
We often say life is miraculous. Here was a statistic to back that up. To reach maturity, each brittle star has to be the very fittest—and luckiest—of the fit. The same holds true for many other organisms in the coral realm, including corals themselves. Repeat such one-in-a-million success stories every generation over millions of years, and an amazing array of forms with spectacular adaptations becomes not just possible but probable.

Three days later we jumped in on Hastings Reef. Within easy reach of the port city of Cairns, it turned into the busiest spot we had yet seen as arriving boats discharged divers and snorkelers. The locale had a worn look that came from a lot of flippered feet kicking the reef and hands grabbing for a closer look. But it was also under assault by crown-of-thorns, the huge, spiked, poison-tipped sea stars that dine on live coral.

As I hovered by pajama cardinalfish—think chubby minnows in clown outfits—a diver came by and thrust a long spear into one of the stars. Periodic outbreaks of crown-of-thorns can strip reefs of color and life. While scientists debate whether these are natural events, like wildfire, or the result of human activities, such as the overharvest of fish that eat juvenile crown-of-thorns, tour operators hire people to remove adult stars daily from popular sites.

There are only 3.5 million residents in the entire state of Queensland, but the growing city of Cairns receives nearly 800,000 international visitors yearly. Most come for a look at the Great Barrier. That the sumptuous reefs in crystalline water shown on travel posters lie 25 miles (40 kilometers) or more offshore often comes as a surprise. Boarding one of the high-speed catamarans that carry as many as 300 passengers there at a time, I found crew members stationed up front with determined smiles and rubber gloves, ready to deal with seasickness bags.

Once we reached Agincourt Reefs, the craft docked at a huge, stable platform anchored by cables. Some groups headed out on guided diving or snorkeling tours. I opted for the ten-minute helicopter overview of the turquoise shoals. Afterward I sat beside a German grandmother to motor past coral walls in a glass-sided semisubmarine, then cooled down in the roped-off snorkeling area. Looking at the paddlers around me, I realized that one way or another, folk of every age and ability were getting to experience a world long beyond the reach of most travelers.

After the Cairns area the most visited part of the Great Barrier is the Whitsunday Group, islands located in the Central section, where reefs are more widely scattered than those farther north. The archipelago is a favorite of both foreign travelers and Australians on holiday, especially sailing enthusiasts. Since it sprawls close to the mainland, the waters aren’t very clear. Yet when I submerged 30 feet (9 meters) off Hook Island, I found a thriving mix of hard corals. Among them was an even richer assortment of soft corals, swallow-tailed sea slugs with electric colors, and scores of fish new to me.

I never did identify the little yellow one that kept scooting up the loose wet suit sleeve of my diving companion, Amanda Parr. She and a boatful of locals were replacing marker buoys encrusted with marine growth. Such floats guide boaters to mooring buoys put in place to relieve anchor damage to the islands’ reefs.

Alongside Parr, a dive instructor, were Tony Fontes, who trains dive instructors, and Elmer Ten Haren, who oversees dive operations for a tour company. These people make their living in the water. Here they were getting wet again on their day off and working for free. When I asked why, Ten Haren answered simply, “Because it needs to be done.”

Neither the Queensland Parks department nor the Great Barrier Reef Marine Park Authority has the manpower to keep on top of all the chores called for along the vast reserve they are charged with managing. “That’s where we come in,” said Fontes, co-founder of a volunteer group that calls itself the Order of Underwater Coral Heroes. “We use our diving expertise to maintain buoys, clean junk off the reef, help with research projects, and educate the public. We didn’t choose the name to sound noble. We liked the acronym O.U.C.H. It lets us tell people that’s how coral feels when you drag an anchor across it.” Just the same, I added genuine heroes to the list of life-forms I had encountered along the reef.

That list, growing longer hourly, led me to James Cook University in Townsville, the main coastal city along the Great Barrier’s Central section. I wanted a professional opinion as to why reef life was such a parade of forms and hues. Why 20 look-alike butterflyfish species instead of, say, two or three?

David Bellwood, a leading marine ecologist, replied, “The answer is that we really don’t know. But I can tell you that a lot of the diversity within groups of tropical fish is a matter of historical accident. It may be that as sea levels fell during the ice ages, ocean basins became isolated, and their populations evolved along separate lines, which we now regard as separate species. Later, when sea levels rose again, many migrated to Australia and took up residence side by side.”

And the communities continue to flourish today. “The best management decision Australia ever made was to put its reef far offshore and along the northern end of the continent, which hardly has any people,” Bellwood said jokingly. “We have some overfishing, but this is one of the few countries that has yet to make its big mistakes with coral ecosystems.”

On the other hand, the coral realm is not immune to the changes taking place in ecosystems on land. Cane fields, other croplands, and development along Queensland’s coastal plain have replaced many seaside wetlands, the natural filters for fresh water coming from the continent. Coupled with deforestation, overgrazing by livestock, and runoff from towns, farms, and industries upstream, this sends more sediments and nutrients flowing out toward the Great Barrier. The total has quadrupled since colonial times. Corals can persist in surprisingly murky water as long as tides and currents periodically sweep the sediments off. It’s the nutrients that wreck a reef. Anything beyond moderate levels of nitrogen hurts growth and reproduction in corals while fertilizing free-living algae that can smother their neighbors.

Drilling down into coral reveals distinct bands whose thickness is a measure of annual growth, rather like the rings in a tree trunk. “Our samples show that some reefs have stopped growing lately,” Jon Brodie, a water-quality expert with the Marine Park Authority, told me. “We can tie this directly to higher nitrogen levels in the water coming out of rivers. But it’s important to point out that when we say the Great Barrier Reef is at risk, we’re only talking about portions of the inner reef so far. More remote areas and the outer reef as a whole are still in good shape.”

Experts worry about an apparent rise in the frequency of bleaching, a condition whereby corals lose their symbiotic algae and turn white, most often when the water gets unusually hot. Prolonged bleaching kills corals. Yet as Terry Done, a senior research scientist at the Austra¬lian Institute of Marine Science, pointed out, disturbance and renewal are common in coral ecosystems and can even add to their diversity.

Reefs proceed from infancy to maturity, sometimes followed by senility, when erosion outstrips growth. At every stage corals are subject to periodic bleaching and crown-of-thorns outbreaks. Not to mention hurricanes; a typical reef on the Great Barrier gets hit every 20 to 50 years. “Before you make pronouncements about the health of any reef,” Done concluded, “you have to know its age and where it stands in recovery from the most recent disturbance. We need to get away from the notion that reefs everywhere at all times should look like the perfect undersea garden in a travel brochure.”

A week later I was exploring a reef that, like the garden of biblical Eden, had a problem with snakes. After cruising steadily northeast from the port of Gladstone, we were a hundred miles offshore in the Swain Reefs complex of the Mackay/Capricorn section, the Great Barrier’s widest belt of reefs. Sea snakes were everywhere, wriggling in and out of coral branches after small fish and eels. Though their venom is deadlier than a cobra’s, these marine serpents aren’t bad tempered as a rule, just unnervingly curious.

A five-foot-long (1.5-meter-long) olive sea snake followed my son, Russell, all the way around a reef, seemingly fascinated by his blue flippers, nosing them whenever he paused. Higher up I found David Doubilet staring through his camera viewfinder at a poisonous stonefish, oblivious to the fact that he had a far more toxic sea snake about to insinuate itself under one armpit and a shark checking out his other side.

We all needed thick rubber suits because the water here was several degrees lower than in the Far Northern section. The reefs’ coral cover wasn’t as dense as before, and there were fewer fish species, though the place was still a Mardi Gras of fins and scales. I was trying to tell several kinds of angelfish apart when a light absorbing hulk the size of a minibus showed up. It was a 700-pound (300-kilogram) Queensland grouper. That afternoon still wider manta rays and eagle rays came flying through clouds of plankton in the tidal current.

A mother and baby bottlenose dolphin arrived toward evening for a long visit around the boat. Farther off more dolphins arced from a silken sea into a papaya-colored sky. But the calm within this shallow labyrinth of reefs was misleading. Crossing open water the next evening, the ship was taking ten-foot-high (three-meter-high) waves abeam and shuddering with each blow while the wind blew 40 knots in the thickening darkness and I made deals with God.

The lighthouse marking North Reef came into view long after midnight. “About bloody time,” Capt. Norm Joseph growled as we made for the protected side. I had tried to analyze reefs in terms of geology, ecology, and management. At that moment I was merely grateful beyond words that reefs existed.

The next night I was lulled to sleep by the mewling of wedge-tailed shearwaters on southerly Heron Island, where seabirds gather by the tens of thousands each night during the nesting season. Our own long journey was nearly over.

After crossing the island to a research station run by Queensland University, I met Ove Hoegh-Guldberg, whose research team may have made an intriguing discovery. “At shallow depths sunlight here can actually be toxic,” he began. “Corals have special pigments to absorb the ultraviolet rays, and their symbiotic algae hide in the shade beneath bundles of these pigments for protection. Conversely, at depths where little sunlight penetrates, the algae nestle right inside the coral’s pigment bundles. Then, as the pigments re-radiate the light energy they have gathered, the algae can use it for photosynthesis.” This re-radiation causes corals to fluoresce a phenomenon that Doubilet had photographed before anyone fully understood how or why it occurred.

Beach walking away from the research station at low tide, I came upon adults bent over, scooping sand like kids making castles. They turned out to be students led by Adrian Jones, a University of Queensland marine ecologist. “I look at these flats as big green leaves,” he said. “All sorts of microscopic algae and photosynthetic bacteria turn out to be living among the sand grains, and our measurements show that they put out as much oxygen as an equal area of tropical rain forest canopy. They also produce complex sugars that bind sediments and help keep the whole reef structure together.”
A lifelong diver, Doubilet was always reminding me how the invention of scuba suddenly opened humanity’s eyes to a realm that had remained a mystery since time immemorial. I pressed my toes into the warm, damp sand. How often had I strolled over bright tropical beaches, never imagining that they too were a scarcely known frontier suffused with one-in-a-million creatures?

Everything about the Great Barrier Reef felt like a revelation. To truly understand the rock-solid, organic fantasia that is a coral reef, we may need to assemble the most sophisticated knowledge, technology, and theorems available. Then again, maybe we will step back with a nod and say: This is what life on Earth does, given warm water, sunlight, and time.

Subscribe to National Geographic magazine.

Sights and Sounds
Tour this extraordinary aquatic world with photographer David Doubilet and meet the exotic creatures that thrive there.

Photographer David Doubilet describes one of the planet’s “great pulses of life.”

Final Edit
The one that got away from our coverage of Australia’s Great Barrier Reef is this month’s Final Edit.

The Australian government has done a remarkable job protecting the Great Barrier Reef. What successful conservation efforts are you seeing in your area? Tell us about them.

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

When it comes to diversity, coral reefs have just about every other terrain beat. The same may hold for coral terminology. Coral and reef terms have specific meanings. To find out what they mean, read on.

A coral is a colony of many individual coral animals called polyps that are derived from replication of an original polyp. A coral reef is made of “squillions” of coral colonies plus other limestone depositing organisms, growing on and among the skeletons of their predecessors, and the sands and silts derived from them. On the Great Barrier Reef, depending on where it grows, a reef can be either a ribbon reef (on the continental shelf edge), a platform reef (on the shelf), or a fringing reef (along the continental islands and mainland).

Great Barrier Reef Marine Park Authority
The official website of the Great Barrier Reef Marine Park provides information about visiting the park and important conservation issues concerning the reef.

Australian Institute of Marine Science
This organization, founded by the Australian government “to generate the knowledge needed for the sustainable use and protection of the marine environment,” hosts a site that includes guides on coral bleaching, crown-of-thorns starfish outbreaks, pollution, and dangerous marine animals.

CRC Reef Research Centre
The center, established by the Australian government, provides scientific information, education, and training to enhance reef-based industry and park management. Check out the section about the effects of fishing on the reef.

Want to know about a fish, almost any fish? Fishbase, a comprehensive online database of the Earth’s fishes, includes more than 25,000 species. Listings include photos, physical descriptions, geographic distribution, environment, and more.

Quicksilver Tours
One of many companies that offer daytrips to the Great Barrier Reef, Quicksilver’s catamaran, semisubmarine, and helicopter rides were enjoyed by author Doug Chadwick.


Allen, Gerry. Marine Fishes of the Great Barrier Reef and South-East Asia. Western Australia Museum, 1997.

Birkland, Charles, ed. Life and Death of Coral Reefs. Chapman and Hall, 1997.

Coleman, Neville. The Dive Sites of the Great Barrier Reef and the Coral Sea. New Holland Publishers, 1996.

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