Seeking Relief for Coral Reefs

Facing new threats from climate change, corals get help from scientists who study the organisms’ complex biology

07-19-2012 // Laura Tangley

Mote Marine 

THE PROJECT WAS NOT MUCH TO LOOK AT:  two tidy rows of 10-gallon aquariums tethered by clear plastic tubing to a pair of cisterns supplying a steady stream of water. Not a single colorful tropical fish graced these saltwater tanks. The only living things they did contain were a few dozen thumbnail-sized pieces of coral, each brownish bit glued to a small cement block resting on the bottom.

But this unassuming experiment, launched last January at Mote Marine Laboratory’s Tropical Research Lab on Summerland Key, Florida, represents the first step of an ambitious new effort that may help scientists rescue coral reefs throughout the Caribbean and beyond. The clue: two lime-green pH meters, one affixed to each seawater-supplying cistern. The first, labeled pH 8.2, “reproduces average acidity of the world’s oceans today,” explained biologist and lab director David Vaughan. The second, reading pH 7.4, dispenses water at an acidity projected to be reached by the end of this century as a consequence of carbon dioxide (CO2) pollution.

The world’s oceans naturally absorb carbon dioxide from the atmosphere. But these days they are taking in too much of the gas. Scientists say that about a third of all human-produced CO2 emissions are ending up in the ocean—and they are radically altering its chemistry, both reducing pH (increasing acidity) and depleting compounds that corals and other marine organisms need to build their calcium carbonate shells and external skeletons. According to the National Oceanic and Atmospheric Administration (NOAA), sea-surface waters have grown approximately 30 percent more acidic since the start of the Industrial Revolution. By 2100, they are likely to be between 150 and 250 percent more acidic—pH values lower than the oceans have experienced in at least 20 million years.

That is particularly bad news for corals, clams, crabs, oysters and other calcium carbonate–dependent creatures. But because these organisms are keystone species in many marine food webs, entire ecosystems are at risk as well. Moreover, “we now have evidence that ocean acidification affects not just calcification but many other marine biological processes, including nitrogen fixation, photosynthesis, reproduction and carbon cycling,” says marine ecologist and geologist Joan Kleypas of the National Center for Atmospheric Research (NCAR).

Coral scientist David Vaughn grows coral at Mote Marine LaboratorySuch findings worry many scientists. “For years, when marine scientists talked about climate change, we were concerned mainly about the effects of higher water temperatures,” says biologist Michael Crosby, Mote’s senior vice president for research. “Today we know that ocean acidification will be the most significant challenge facing marine environments in the decades to come.” Patty Glick, NWF’s senior climate change specialist, agrees: “Since I began working on climate change and coral reefs more than a decade ago, concern about ocean acidification has transformed into true alarm.”

Last year, NWF launched a five-year partnership with Mote, with initial work targeting “science-based coral reef ecosystem restoration.” The project on Summerland Key (above) is critical to such efforts. Made possible by a unique 80-foot-deep well that supplies naturally acidic, CO2-rich seawater, the experiment initially is comparing the health and growth of three kinds of coral—great star coral, boulder star coral and diffuse ivory bush coral—in water at today’s ocean acidity versus what is projected by the turn of the century. (Bubbling air into the high-acidity tank drives off CO2, raising pH to today’s value.) Once the protocol is refined, researchers plan to add other coral and noncoral species to the system as well as test assemblages of organisms found together in the wild. “We want to learn which species and which genetic strains are most resilient under ocean conditions expected in the future,” says Vaughan—results that are key to restoring beleaguered coral reefs.

Last Straw?

Coral reef off the coast of MexicoThe planet’s most biologically diverse marine ecosystems—home to at least 800 coral species and more than 4,000 fish species—coral reefs have been struggling for decades. From the Florida Keys and elsewhere in the Caribbean to Southeast Asia to the Indian Ocean, reefs are being devastated by a combination of pressures, including coastal development, pollution, soil erosion, invasive species, overfishing and destructive fishing practices such as the use of dynamite and cyanide. In most places, coral ecosystems are confronting several of these stresses simultaneously.

The most recent threat, and ultimately the most serious say scientists, comes from climate change. As CO2 and other greenhouse gases have built up in the atmosphere, the average temperature of water surrounding reefs increased about 0.9 degrees F between 1870 and 2005, and oceans are heating up even faster today. Combined with local stresses, warmer waters have increased the incidence of coral bleaching, which occurs when corals expel symbiotic algae that both nourish and give them their vibrant colors. First reported in the 1980s, mass coral bleaching events have become both more frequent and widespread. Though some corals recover from a temporary loss of symbiotic algae, many die, and those that survive become more susceptible to diseases—which also are on the rise.

Last year the World Resources Institute, in collaboration with more than two dozen national and international partners, released a report, Reefs at Risk Revisited, concluding that three-quarters of all coral reefs are threatened. By 2050, without significant changes, nearly all reefs will be at risk. According to C. Mark Eakin, who coordinates NOAA’s Coral Reef Watch program, “In recent decades, we already have lost more than 20 percent of the world’s coral reefs.” Given these grim figures—and growing awareness that ocean acidification prevents corals from rebuilding—many scientists are turning their attention to restoration. Says Crosby: “Human intervention absolutely will be required to bring back the world’s coral reefs.”

Coral Gardeners

Five miles off Summerland Key, human intervention is well under way in the Florida Keys National Marine Sanctuary. At the stern of the research vessel Lady Lynne last January, Mote staff scientists Erich Bartels and Cory Walter pulled on wetsuits and stuffed the pockets of their dive vests with toothbrushes, putty knives, cattle ear tags and other supplies on a cool,  cloudy morning. Perching briefly on the edge, they flipped backwards into the turbid water. Leaving only bubbles visible from above, the scientists sank 30 feet to the seafloor to tend their “garden”—a 35-square-meter plot of staghorn coral fragments affixed to cinder blocks lined up in rows. During the next hour, Bartels and Walter worked quickly and meticulously, scraping off algae, replacing missing ID tags and inspecting each fragment for signs of bleaching or disease.

From an initial planting of 100 staghorn fragments five years ago, this underwater nursery, paid for by federal stimulus funds provided through The Nature Conservancy (TNC), has grown to a crop of more than 3,000 tiny corals that researchers are beginning to replant on dead or damaged reefs. Once the most common coral species throughout the Florida Keys—and the Caribbean’s most important reef builders—staghorn and elkhorn corals began declining sharply in the 1980s. In 2006, both species were designated as threatened under the U.S. Endangered Species Act. “Staghorn and elkhorn corals were once the oaks and maples of the Keys’ coral forest,” recalls Vaughan, who has been diving in the region since the 1960s. “Now 98 percent of them are gone.”

Coral gene bank at Mote Marine LaboratoryMote’s staghorn garden is one of eight similar coral nurseries coordinated by TNC and distributed from the Upper Keys south to the U.S. Virgin Islands. Containing 30,000 fragments and growing, the network represents the world’s largest coral restoration effort. Just as important, the project also is the first to identify and manage the genetic makeup (genotypes) of its corals (right). Indeed, beyond increasing the amount of staghorn in the Keys, Bartels and his colleagues want to boost the corals’ genetic diversity. “To reproduce sexually, corals must be physically close to corals of a different genotype,” he explains. Yet on many reefs today, that cannot happen because the few surviving corals are clones of a single parent. “We cannot bring back the reefs by replanting them all,” says Bartels. “But what we can do is give corals a jump start: establish diverse enough populations so they can come back on their own.”

Genetic diversity also is critical to corals’ ability to adapt to the planet’s rapidly changing environment. Already, Bartels and his colleagues have discovered that some staghorn genotypes resist bleaching or disease better than do others. Once the scientists have established self-sustaining populations on the reefs, they plan further lab tests of the natural resilience of different genetic varieties. Which ones hold up the best in warmer waters? At higher acidity? In the presence of common coral diseases? “If the corals we restore today cannot survive ocean conditions in 50 or 100 years, what we’re doing is only a short-term solution,” Bartels says.

Beneficial Bacteria

At Mote’s main laboratory in Sarasota, Florida, microbiologist Kim Ritchie is pursuing another strategy to boost the natural resilience of corals. As anyone who has taken a high school biology class probably knows, corals are tiny animals called polyps. Critical to polyp survival are symbiotic plants—algae called zooxanthellae—that in exchange for a safe place to live, produce oxygen and energy to nourish corals. Now Ritchie is proposing that a third player may be involved in the relationship: symbiotic bacteria that help keep corals, and perhaps zooxanthellae, healthy.

For the past eight years, Ritchie has been collecting mucus from the surface of healthy elkhorn corals in the Florida Keys marine sanctuary. Analyzing the substance in her lab, she’s discovered it harbors several kinds of bacteria that produce disease-killing antibiotics. “For a long time, scientists have been studying coral diseases—what makes the organisms sick,” says Ritchie. “What’s more interesting to me is what keeps corals healthy. If you don’t understand its immune system, you won’t understand why a coral is sick.”

Bolstering her case for beneficial bacteria, Ritchie also has discovered that when seawater temperatures rise, the composition of bacterial species present in coral mucus changes.  Specifically, “the Vibrios increase, and the Pseudomonas decline,” she says. Ritchie believes this shift makes corals more vulnerable to disease-causing microbes—similar to when people develop diarrhea after antibiotics disrupt the balance of “good bugs” in their intestines. Her findings may help explain why corals frequently develop white pox, black band and other devastating diseases soon after a bout of bleaching.

Ritchie’s results also may offer new ways to fight, or at least prevent, coral disease. “We’re not revving up the engines of our spray planes to inoculate reefs with bacteria just yet,” says Billy Causey, Southeast regional director of NOAA’s Office of National Marine Sanctuaries. “But this work does provide a potential tool for resource managers trying to protect coral reefs in the future.”

Even as Ritchie and her colleagues work overtime to help corals, some experts fear the pace of climate change and other assaults is growing too quickly and that reef ecosystems may vanish in the coming decades. “I’m an optimistic person, so I don’t predict doomsday for reefs—just yet,” says NCAR’s Kleypas, who recently received the Heinz Award for her work on climate change and coral reefs. “In the future, reefs probably will make it in at least a few places,” she adds. “But they’re likely to look more like marginal reefs and less like the big vibrant structures most of us think of today.”

Senior Editor Laura Tangley visited Mote Marine Laboratory last January.


NWF Priority: Climate Change and Coral Reefs

Bahamas reef sharkCombating the effects of global warming on critical wildlife habitats—including coral reefs—has been a top priority at NWF for many years. The Federation is backing federal legislation to promote clean energy, for example, and to reduce the pollutants that fuel warming. Last year NWF bolstered its policy work by launching a five-year partnership with Mote Marine Laboratory, a global leader in ocean science since 1955. The groups will collaborate on projects to protect reefs and other marine ecosystems, targeting the perils posed by climate change. “The threats to our marine life and habitats have never been greater,” noted NWF President Larry Schweiger when announcing the partnership.

To learn more about NWF’s work on coral reefs, see

For more on Mote’s research programs, go to

Help support NWF’s work to combat climate change and other threats to wildlife.

Online Exclusive: View a slideshow of animals that live on coral reefs.
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