09 May 2011

The Damage Ninety percent of Australian and Indonesian reefs [red] are threatened by bleaching. Graham Murdoch

In the past 20 years, nearly a third of the world’s coral has been destroyed. Around 90 percent of the reefs off the coasts of Sri Lanka, Tanzania, Kenya, the Maldives and the Seychelles are at risk. If ocean temperatures rise by another 7ºF in the next three decades, as is predicted, 95 percent of the Great Barrier Reef will disappear. The primary cause of the die-off is coral bleaching. As temperatures rise, marine bacteria flourish and attack the algae that live symbiotically within every individual coral polyp. The algae photosynthesize sunlight into energy (in the form of sugars) for their hosts and give coral its color. When the algae dies, what’s left is a ghostly white.

Some corals in the Red Sea and the Persian Gulf have avoided this fate, although no one knows exactly why. Eugene Rosenberg, a microbiologist at Tel Aviv University, has proposed that the presence of a different form of bacteria is what has made the difference. “Coral has thousands of bacterial species living within it, just as humans do,” he says. “These bacteria can help coral adapt to environmental changes.”

When water temperatures rise to 77º in the Red Sea, for instance, a nonresident species of bacteria called Vibrio coralliilyticus attacks the algae of some corals. But that same temperature spike may also trigger some of the corals’ bacteria to defend the algae, which could explain why certain corals aren’t susceptible to bleaching even at high temperatures.

Now Rosenberg and his colleagues are investigating how to boost all corals’ natural defenses. One tactic involves unleashing bacteriophages—bacteria-attacking viruses—on V. coralliilyticus. In recent lab experiments, the phages quickly destroyed the bleaching bacteria and remained on the coral for two months, staving off further attacks. This summer, in parts of the Great Barrier Reef and the Red Sea’s Eilat Reef where some spotty bleaching has occurred, Rosenberg will field-test “phage therapy.” He will surround diseased coral with healthy corals, and in one sample he will introduce a phage. If things unfold as they did in the lab, the phage will attach itself to V. coralliilyticus. When the attacking bacteria reach the nutritionally rich mucus layer of the healthy corals, the phage will multiply 100 times over and overwhelm its host. Rosenberg predicts that his phage-less control samples will become bleached in a week or two.

If he gets positive results, the next logical step will be a much larger-scale application. Rosenberg says that with a little more than 13 gallons of liquid, mixed at a concentration of four million phages per gallon, he could treat roughly 30 miles of coral. The application would require a boat or a plane. “We’re talking about covering a lot of reef,” he says.

09 May 2011

Low Lifes Ocean "desert" areas, pinpointed on the map above, grew from 17 million square miles in 1998 to almost 20 million in 2007. Graham Murdoch

As the atmosphere warms, the water cycle—the process by which seawater evaporates, rains down, and then evaporates again—will intensify. Everywhere, the ocean surface will become, on average, saltier. The extra evaporated water vapor will rain down disproportionately in areas such as the tropics and Scandinavia, bringing stronger storms and more frequent floods. Meanwhile, the areas just north and south of the tropics, which already tend to be saltier than other regions, will become saltier and warmer. In the very saltiest areas, existing “desert” areas—those too salty to host most life—could grow.

The salt fountain raised chlorophyll levels a hundredfold.So far, scientists have been able to do about as much to reverse the intensification of the water cycle as they have to control any other aspect of the weather: not much. But one technique, Ocean Thermal Energy Conversion, or OTEC, might help. In the 1970s, engineers began using platform-based rigs to bring cold, deep water to the warm surface; the idea was that the temperature difference would drive a heat engine, generating energy. Used on a large scale, OTEC could have the healthy side effect of lower the surrounding surface temperatures, and that would be a very good thing.

“If we lower the seasonal surface temperature, then we should expect the water cycle to become less intense,” says Ray Schmitt, an oceanographer at Woods Hole. The first wave of OTEC research died when the last demonstration plant closed in 1998, but now an OTEC revival might be under way. Since 2009, the U.S. Navy has paid Lockheed Martin $12.5 million to develop a commercial OTEC plant near Hawaii; an international consortium is considering building another plant in Tahiti.

In the saltiest areas, pulling water from the deep might help create life-rich oases. In 2002, researchers at Tohoku University in Japan began testing a “perpetual salt fountain,” a thin pipe that transports less-salty water from the deep to the much saltier surface. Cold water enters the bottom of the pipe, warms, and then rises—but as it warms, it remains relatively fresh and rich in nutrients that stimulate the growth of chlorophyll and phytoplankton. For their project, the Japanese researchers have deployed a floating, GPS-equipped, 984-foot PVC pipe in the Mariana Trench area in the Pacific Ocean, and the early results are promising.

“Just outside the pipe, the concentration of chlorophyll was enormous,” says Shigenao Maruyama, the head of the research team. “About 100 times larger than in the surrounding sea area.” Like OTEC, the salt fountain would be only a stopgap measure—a way to treat the symptoms of global warming rather than a solution to the underlying problem. But Maruyama is optimistic about the salt fountain’s potential to repair damage on a local scale, and the experiments are scheduled to continue next year with a new salt fountain in the open ocean.