Scientists find a simple solution can give new life to some of the oceans’ most important ecosystems.
Six feet below the surface of the Caribbean Sea, Lisa Carne holds a small ceramic disk with a chunk of elkhorn coral, its curled leafy shape resembling rust-colored kale, cemented onto it. She threads a plastic cable tie through holes in the disk, then fastens the other end of the tie to a lattice-like metal frame, one of a dozen or more anchored to the sandy floor. Carne deftly maneuvers her fins and scuba gear, careful to not disturb the surrounding coral, and repeats the process, attaching the ceramic cookies with their exotic flora onto the metallic grates, which sway rhythmically in the gentle current.
Carne, an American marine biologist and manager of the reef restoration prodeject Fragments of Hope, points to other, more mature coral beds around the caye: Elkhorn corals and spiky white-tipped antlers of staghorn corals, held in place by rope lines tied to large metal frames, are so overgrown that the artificial foundations sag under the corals’ weight. Carne planted these two years ago, the same way she did the other chunks a minute ago, and wants to show off how well they’re growing.
Then, applying broad shoulders developed from clocking in long hours underwater with tanks strapped on her back, she hoists herself back into our fishing skiff. When she removes her mask and regulator her blue eyes and sharp features come into focus. We’re near Whipray Caye, a speck of an island eight miles offshore, in the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site. This spot is the site of one of eight underwater coral nurseries that have been established around Laughing Bird Caye National Park, a protected area encompassing more than 10,000 acres of marine habitat that includes coral patches.
On this humid March day, the sky is crystal clear, with temperatures hovering in the high 80s, and the sparkling sea all around is almost as warm as a hot tub—and significantly warmer even than the water several miles away. Carne is here as part of a last-ditch international effort to save the world’s coral reefs. As humans have filled the atmosphere with carbon dioxide over the last century and a half, the seas’ temperatures are rising, and with them the concentration of CO2 in ocean waters. Adding to the damage have been overfishing, which upsets the ecological balance around reefs, and coastal development, which causes erosion of soil into reef ecosystems. The result is severe bleaching, coral collapse, and disease that have wiped out an estimated 19 percent of the world’s coral reefs, with roughly three-quarters of what remains seriously threatened.
Because marine biologists can’t do much about gas mileage standards for automobiles, deforestation, or coal power, they’re working on restoring reefs, and Carne found out, quite by accident, that certain species of coral do better than others in warmer water. Carne’s program employs methods similar to those at reef restoration efforts now going on across the globe: broken bits of the heat-tolerant coral collected from the sea floor are incubated on the metal-and-rope moorings below the bottom of our skiff, where they grow like tree clippings until they’re full enough to harvest—usually within a year or two. Pieces are then broken off—coral can reproduce like grafted plants—to transplant into the wild, ultimately forming hundreds of colonies of these hardier corals on damaged areas of the reefs. It’s early in Carne’s effort, but if she’s right, the corals she and colleagues are painstakingly coaxing back to abundant life could be deployed in the fight to save reefs from anthropogenic climate change.
“This is critical work because it not only restores the ecological integrity of these habitats in southern Belize, but it provides a testing bed for methods of building reef resilience in the future,” says Nadia Bood, a marine biologist with the World Wildlife Federation in Belize City, which has funded Carne’s work since 2009.
Reefs take up only about 2 percent of the ocean floor, but their value to other ocean ecosystems is enormous: They support a third of all marine life—providing habitat, food, and spawning grounds—which in turn feeds more than 500 million people, who depend on reefs for protection from storms, surges, waves, and coastal erosion, as well as for tourism. At the same time, reefs are widely considered the most vulnerable of the marine ecosystems to the effects of climate change, according to the most recent report from the U.N.’s Intergovernmental Panel on Climate Change, which darkly warned that the reefs are undergoing rapid, “potentially irreversible” declines.
Coral species depend for food on microscopic algae that live inside them, which transform sunlight into energy through photosynthesis. But warming conditions prompt the corals to expel the algae, draining the reefs of color—hence the term “coral bleaching”—and leading to coral death due to the lack of nutrients. Oceans, moreover, absorb about a third of the CO2 we dump in the atmosphere, which indirectly causes the seas’ pH balance to acidify. This change in ocean chemistry inhibits the formation of the calcium carbonate corals need to maintain their shells and dissolves the stony skeletons that support corals and reefs. As a result, they’re collapsing at a faster rate than rainforests. Caribbean reefs are in the worst shape, with 80 percent of the live coral cover lost since the 1970s due to heavy coastal development, hurricanes, overfishing, and climate change.
Belize’s reefs are at the center of the largest reef system in the western hemisphere, the endangered Mesoamerican Barrier Reef System extending from the eastern tip of Mexico to southern Honduras. Normally, the Caribbean reefs run north to south, but in Belize they’re elbow shaped. The unusual geography of the reefs there may be responsible for their corals’ inbred thermal resistance. The inner keys are already hotter than regions around other reefs; these corals are under greater chronic thermal stress and as a consequence, have become more heat tolerant and hardier. “Inside the barrier reef, that area is more prone to higher salinity, hotter temperatures, and greater turbidity from storms,” says Melanie McField, director of the Healthy Reefs for Healthy People Initiative at the Smithsonian Institution in Fort Lauderdale, Fla. “Over thousands of years, corals in those inner reefs have adapted to this environment and are a little stronger than the ones that live in the outer barriers.”
“These waters have been hotter for longer periods of time—some even as high as 90 degrees Fahrenheit,” says Carne. “So the coral that survive are naturally tolerant of higher temperatures, and their growth rates aren’t stunted by the hotter waters.”
For years, Carne witnessed firsthand the deterioration of the reefs off the coast of Belize, especially the worldwide bleaching event that occurred in 1998, which was attributed to the double whammy of El Niño and La Niña. “For the first time, all these corals were turning white everywhere, and every place you looked, there was just a constant documentation of decline over and over again,” she says. “It was depressing.”
In 2001, Hurricane Iris slammed into southern Belize with winds of up to 145 mph and decimated the reef, littering the ocean floor with dead coral husks. Laughing Bird Caye National Park took a direct hit; the caye was split in half. The hurricane “washed over everything,” says Carne, who was a manager at Glover’s Reef Marine Reserve at the time. “Everything was dead and stank to high heaven with all these dead organisms all over the park.”
Virtually no elkhorn or staghorn coral colonies were left alive. These two fast-growing, branching species, which provide crucial scaffolding to the reefs and habitats for hundreds of other marine creatures, were once the most common corals in the Caribbean. But their abundance has been reduced by more than 98 percent in just a few decades because of climate change, landing them on the International Union for Conservation of Nature’s critically endangered list (one step away from extinct in the wild). Nonetheless, Carne noticed, the corals survived in some areas of the Belize reefs and grew back faster than did other species. This suggested to her that they were hardier and better able to withstand the increasingly hot ocean temperatures. “I spent a week out on the water with the fishermen and tour guides and discovered something amazing,” she says. “In the warmer parts of the reef, there were these beautiful patches that were just pristine and healthy, with all this gorgeous elkhorn coral that had been wiped out everywhere else.”
That’s when Carne came up with the idea of transplanting the more robust corals to reforest the reefs and “give Mother Nature a boost,” she recalls. “I thought I was a genius at the time, but when I Googled it, it turns out there were a few people doing this—although not nearly as many as today.”
Since the mid-1990s, she found, marine biologists have been using coral nurseries to fortify stocks in rapidly dwindling reefs. The practice started with Israeli scientists, who did the first successful experiments—also using elkhorn corals—in the Red Sea. Though the idea of using chipped, cemented-together pieces of coral to patch damaged reefs seemed wildly improbable—more like something out of “There, I Fixed It” than the hypothesis of a rigorous scientist—the strategy worked, and the finicky, slow-growing corals flourished. Most of the techniques now in use were perfected on reefs in the Pacific, and more than 60 of these projects are under way throughout the Caribbean, at sites in Mexico, the Cayman Islands, the Dominican Republic, the Bahamas, and Belize, as well as in Florida. “We’re now working at an ecologically meaningful scale with thousands of genetically diverse strains of coral re-deployed in the wild every year,” says Diego Lirman, a marine biologist at the University of Miami. “But we’re realistic—it’s virtually impossible to rescue entire reefs through simple restoration. What we can do is accelerate the reef’s natural recovery processes.”
This is critical work because it not only restores the ecological integrity of these habitats in southern Belize, but it provides a testing bed for methods of building reef resilience in the future.— Nadia Bood, World Wildlife Fund
It took Carne five years to get funding to test this idea in Belize. With a small grant from the Protected Areas Conservation Trust, Carne pasted 19 fragments of elkhorn coral to the dead reefs in Laughing Bird Caye National Park. A few months later, she found the corals were thriving. Emboldened, she secured funding from the World Bank and the World Wildlife Fund, among others. Since 2006, Carne and her cohorts, who include fellow scientists, students and teachers from local high schools and colleges, and environmental activists, have painstakingly planted more than 8,000 coral fragments around Laughing Bird Caye National Park.
We make a brief stop at the coral nurseries off French Louie Caye, where Carne loads two large plastic tubs with the long, spiky branches of staghorns that she breaks off from the thicket of corals sprouting on their artificial frames. Then we head over to Laughing Bird Caye. Here in the reef-filled waters surrounding the caye—a picture-perfect acre-and-a-half sliver of gleaming white sands, coconut palms, and mangroves, with a cluster of picnic tables where diving and snorkeling expeditions congregate for lunch—the restoration’s results are most evident.
Interspersed with the teeming marine life of the reef, next to the boulder-size brain corals, the delicate sea grasses, the fluttery sea fans, and the fire corals, are dozens of colonies of nursery-grown corals: majestic outcroppings of fully grown elkhorns, with leafy branches extending five feet or more, and the massive domes of staghorns, which, with their white-tipped tendrils, look like giant mums.
“Roughly 80 percent of the corals we transplant survive,” says Carne as she sits on the boat deck. Sloshing around in the water-filled plastic tubs, she uses diving weights to break up the staghorn branches into pieces about an inch or two in length. Then we push each of the spiny fragments between strands of rope, seeding the rope’s length with dozens of pieces. They look like giant rock candy necklaces. The ropes are then woven through metal frames sitting on the sea floor. Within the year, they will be overgrown with healthy staghorns, and Carne will come back to break some off and seed it elsewhere on the reef.
“We’ve triggered a cascade of destruction with climate change,” says Les Kaufman, a professor of biology at Boston University who specializes in reef restoration. “But by tweaking that system at even a tiny scale, and learning through projects like this about how reefs recover, we might be able to engage their natural healing mechanisms with enormous multiplier effects. That is what we’re hoping the coral nurseries can accomplish.”