Shark humor has its time and place, but not when I'm snorkeling somewhere called Shark Bay. At the Heron Island Research Station, a laboratory on the teardrop-shaped atoll 45 miles (72 km) off Australia's east coast, the suntanned, chirpy station manager gives a parting wave to the three students who are taking me out for my first look at the legendary corals of the Great Barrier Reef. "Just don't get eaten, will you?" she says. Ha-ha. Happily, there are no sharks in Shark Bay that morning; in fact, there's not a whole lot of anything. As I follow the students' snorkels, we pass over circular beds of brown, monochromatic coral and empty expanses of rippled sand. A handful of small, glimmering fish hover in the water column, but they're the only life we see during an hour-long swim. Where are the schools of coral trout? The famed Maori wrasse? Wading back to shore, one of the students shrugs: "Sorry there wasn't more."
The Great Barrier Reef is one of the world's natural wonders, covering an area larger than Italy and drawing nearly 2 million tourists every year to boat, swim, snorkel and dive amid its elaborate flora and fauna. It generates some $6 billion in revenue for Australia annually and provides employment to more than 50,000 people. It's also one of the planet's most fragile ecosystems, home to more than 11,000 species that live, if not necessarily in harmony, in a carefully orchestrated symbiotic balance. At the foundation of this giant ecological and commercial enterprise is one tiny marine organism: the coral.
That foundation is no longer solid. Corals build colonies that secrete calcium carbonate to form ocean reefs. When they're healthy, coral reefs provide shelter and food for animals all along the food chain, including the top: us. Across the planet, half a billion people rely, directly and indirectly, on corals for their living. That's why what happens to the 9,000-year-old Great Barrier Reef, as well as to other reefs worldwide, is critical. The recent Queensland floods were most notably tragic for the lives lost and property destroyed. But they have also hurt the Great Barrier Reef by funneling into the ocean vast plumes of freshwater and agricultural runoff that could severely damage the coral. Besides the extreme rain that sparked the floods, rising ocean temperatures, changes to the ocean's chemistry and the global trade in natural resources all symptoms of our fossil-fuel economy are waging a multifront war on the marine environment. "You can't walk into a forest and start hacking at branches and killing off animals and denuding the forest cover without killing the trees," says Justin Marshall, a marine biologist at the University of Queensland. "The outlook for the whole reef is poor."
What's even more worrying is that nearly all other coral reefs are in worse shape than the reef of northeastern Australia. The 1,430-mile (2,300 km) Great Barrier Reef is a UNESCO World Heritage site and the world's largest protected reef system. Belonging to a wealthy and sparsely populated nation has helped protect it from the rampant overfishing and overt destruction seen in places with less government money for conservation and more people who rely on reefs for food. "One hundred years ago, many countries had reefs like the Great Barrier Reef," says Ove Hoegh-Guldberg, the director of the University of Queensland's Global Change Institute. "They probably thought they were robust and weren't going to fall over, but, of course, they did. The Great Barrier Reef is a reminder of what's at stake."
Up in the Air
Above the clear water off Heron Island, a single windmill whirs in the breeze, its legs anchored in the shallows while it sends power to a tangle of computers and carefully looped cables perched on floats a few feet away. The computers are measuring, among other things, the pH levels of the water flowing through four plastic chambers mounted on the reef. The information gathered at this lab could give the world a clue as to what's in store for the Great Barrier Reef and the other 90% of the world's corals. The makeshift station is the first experiment to measure how coral responds in its natural environment to ocean acidification, widely thought to be one of the biggest threats today to marine environments. Oceans absorb about half of the carbon dioxide humans produce, and while that helps lessen the effect of fossil-fuel emissions on the atmosphere, it also causes a reaction that makes seawater more acidic.
That change is bad news for coral. As seawater becomes more acidic, the corals' skeletons become weak and prone to breaking down more easily in situations they would normally withstand, like cyclones or being nibbled at by reef worms. Carbon dioxide levels in the atmosphere have risen nearly 40% from the start of the industrial age, from 280 parts per million (p.p.m.) to about 385 p.p.m. today. Scientists estimate coral and other reef creatures will manage until that number hits 400 p.p.m.; they believe that at 500 p.p.m, hard coral will essentially become extinct, and reefs everywhere will start eroding. "Being isolated doesn't help you," says David Kline, a researcher at the University of Queensland's Coral Reef Ecosystems Laboratory who is leading the offshore ocean-acidification project. "Even if there are no people living nearby, [the corals] will be affected."
Corals dislike warm water about as much as acidity. When oceans get atypically warm, corals can eject the algae that symbiotically live in their skeletons, providing food in exchange for shelter. The ejection process is called bleaching, named for the white skeleton left behind when the coral gets sick and, in some cases, dies. As atmospheric carbon dioxide levels continue to rise, global warming will increase ocean temperatures and, along with that, the frequency and severity of bleaching events. A mass bleaching in 1998 killed 90% of the corals in the Indian Ocean. In 2010, one of the hottest years in recorded human history, reefs bleached throughout the Caribbean and the Indian Ocean and off the coasts of Thailand, Cambodia, Malaysia and the Philippines. If the oceans' corals collapse, the whole food chain might too.