A solitary block of pale-yellow branching corals rises from the white-sand ocean bottom just off the coast of Punta Cana, a tourism center at the easternmost tip of the Dominican Republic. Schools of small fish weave in and out of the crevices. They’re staking out a rare hiding spot—a critically endangered coral that has been painstakingly cultivated by the Puntacana Ecological Foundation (PEC), an environmental organization here.

This staghorn coral (Acropora cervicornis) the fish are swimming through is among a group of corals that in the last 30 years has seen drastic population declines in the reefs of the Dominican Republic and much of the Caribbean. But while their numbers remain alarmingly low in the wild, the corals thrive on the ropes and A-frame metal structures in manmade underwater coral gardens created by the foundation.

The gardens, once considered a last-ditch preservation effort, have proven to be an effective tool for repopulating the Dominican Republic coast’s shrinking reefs. Scientists, conservationists and even tourists are now teaming up to expand the project’s scope in hopes of saving these crucial marine habitats.

In the late 1970s and early 1980s, a never-before-seen coral disease swept across the entire Caribbean, turning once healthy corals into dead, white rocks. The disease affected acroporid corals, which are the primary reef builders in the region, making them crucial to the structural integrity of the reefs.

Biologists named the mysterious illness white band disease for the characteristic white strips of dead coral it left behind. Able to spread up to one centimeter per day, white band disease proliferated quickly on its own, but the disease was elevated to a full-blown epidemic due to a massive die-off of Diadema sea-urchins. Without the urchins to graze on the reefs, an overabundance of seaweed built up on the coral, trapping bacteria.

During this period, 95% of the region’s staghorn and elkhorn (Acropora palmata) corals died off and other species of acroporid corals were severely affected. In the decades since the outbreak, scientists have been unable to pinpoint the source of either white band disease or the urchin deaths, though new studies indicate the former may have been spurred by improper sewage disposal. Despite conservation efforts to cut down on coastal pollution in the Dominican Republic, the island’s reefs continue to face white band disease and other threats to their survival.

Notable among the other threats is coral bleaching, which can occur when an increase in water temperature causes coral to eject symbiotic algae that helps sustain it. Though the coral turns white, it can still be alive; but it is at a heightened risk of dying.

Since the turn of the century, rising water temperatures have pushed the island’s reefs into three mass coral bleaching events. The most extreme of these events to hit the Caribbean, in 2005, bleached 68% of the Dominican Republic’s corals, killing 11%.

Overfishing also continues to take a severe toll on the local reefs. According to environmental groups, more than half of the average fishing catch is made up of parrotfish, which, like sea-urchins, graze on and clean coral reefs. The overfishing of crab, lobster and hogfish has also led to an overabundance of their coral-eating prey, which include fireworms, damselfish and coralliophila.

Overall, approximately 75% of the world’s coral reefs are considered threatened by climate change and human coastal activities. In the Dominican Republic these problems are especially severe due to the region’s vulnerability to extreme temperature change and the presence in the region of large coastal populations.

The degradation of the Dominican Republic’s reefs has alarmed business owners as well as environmentalists. According to government data, tourism in 2014 made up 16% of the country’s GDP, and one in six tourists list the beaches as their primary reason for choosing the Dominican Republic as a vacation spot. A 2010 study by the World Resources Institute estimated that the current rate of coral degradation in the country causes beach erosion that could lead to revenue losses of US$52 million to $100 million by 2020.

“Coral reefs produce a lot of the sand and they provide most of the shore protection, so when they disappear those services go away,” says Víctor Galván, ecological research coordinator for the Puntacana Ecological Foundation’s coral gardens. “People started to get worried and wanted to do something.”

For most of its existence, coral gardening was relegated to the hobby aquarium industry. These operations used harvested coral seedlings to grow small chunks of coral and sell them for aquarium landscapes. It wasn’t until the late 1990s, following a major worldwide decline in coral reefs, that scientists started to consider coral gardening as a possible tool for conservation. Environmental groups began launching coral gardening projects in the South Pacific and soon they started to spread to the rest of the world.

The Puntacana Ecological Foundation teamed up with the environmental group Counterpart International to launch the Caribbean’s first coral gardens in 2004, installing small sites off Punta Cana, on the island’s east coast, and in Sosúa, in the country’s north. After organizers had struggled for five years with a fluctuating supply of volunteers to manage the gardens, the University of Miami joined the project and helped assemble a full-time staff. From that point on the project has had one mission: to keep acroporic species from disappearing at a local and regional level.

To do this, the team began by surveying reefs across the country for healthy populations of endangered corals. They specifically targeted corals that seemed to possess the genetic resilience to resist bleaching or white band disease. From each site, a diver can harvest 10% to 15% of the desired species—the maximum that can be taken without harming the plant—by cutting off the ends of coral branches.

Branching corals such as the staghorn and elkhorn can reproduce naturally through fragmentation, with their broken branches serving as the basis for growing a new coral colony.

Divers secure coral fragments in the garden, often referred to as a nursery. Depending on the coral species and the ocean conditions at each site, the fragments are either hung from ropes, strapped to metal frames or secured onto cement disks known as cookie trays. As new fragments grow larger, they form a mother colony that remains in the nursery. As they grow, foundation staff members trim the branches, harvesting new fragments. These, in turn, are used to create other mother colonies or are planted on wild reefs.

Starting with the two original nurseries in 2004, coral gardening has since expanded to seven sites in the Dominican Republic as well as six pilot sites, including one in Haiti.

“At this point, if anything happens and this doesn’t work, we are at least a genetic bank for the species,” says Galván.

Though preserving each coral species’ genes is the primary objective of coral gardening, foundation organizers hope the project’s benefits will extend beyond the nursery. In 2014, the foundation shifted its priority from expanding its nursery to transplanting tissue on wild reefs, where the corals can reproduce naturally.

Corals in many ways look and behave as plants do, but each group of coral is actually made up of tiny translucent creatures knows as polyps. An individual polyp can attach itself to a hard surface underwater and then divide into new, cloned polyps, growing into a reef. While this cloning process makes up a large portion of a coral’s growth, the polyps can also reproduce sexually with other groups of polyps of a different genotype. Once a year, the hermaphroditic corals will have a synchronized spawning event, where they release sacks of eggs and sperm into the water. Each coral’s gametes can only fertilize those of another coral group.

These spawning events require a massive amount of energy from the coral, and the foundation tries to prevent sexual reproduction from occurring in the nursery, where the main goal is to produce as many fragments as possible.

To do this, employees and volunteers regularly trim the mother colonies to keep them in their faster-growing, but sexually unproductive juvenile state. While this method makes sense within the nursery, in the wild, spawning episodes are crucial both for increasing the populations of endangered corals and diversifying the species genetically.

“One sexual episode could see a million juvenile recruits whereas we can only produce about 5,000 fragments in a year,” Galván says. “When you have a population decline 98%, a small coral might be here and another [of the same species] on the other end of the country and their sperm and eggs will never meet during fertilization. So all the effort dies and they die with it.”

By planting coral fragments on existing reefs, the foundation hopes to increase the likelihood of natural reproduction. To date, the foundation has transplanted around 5,000 coral fragments, collectively representing a length of more than 2.7 km (1.67 miles), onto wild reefs.

Once in the wild, these corals currently experience a 10% mortality rate on average. They do face tests. The environmental factors that originally decimated Caribbean coral populations still threaten the region, and temperature rise is expected to worsen in the coming years. Still, while newly transplanted juvenile corals face these challenges, the fact that the original fragments survived at all shows that they come from strong genotypes.

“The corals that are still out there in the wild tend to be resistant to disease and warm temperatures,” Galván says. “Just like people have done with livestock for centuries, we breed the strongest ones to get the traits that we want.”

Puntacana Foundation divers seek out unbleached coral that has survived in warm shallow water. They also examine reefs that have been compromised by white band disease in hopes of finding acroporic corals that have fought off the condition. As these corals are put out into the wild in increasing numbers, not only will their population grow, scientists say, but there will be greater opportunity for them to crossbreed with other strong genotypes. This selective breeding may make future corals more resilient in the face of adverse environmental conditions.

Rather than wait for the chance crossbreeding of a super coral, the foundation also is attempting to address the environmental problems that harm reefs in the first place. For instance, it has undertaken public-education campaigns on the need for reef protection and pushed for fishing regulations. In doing so, the foundation has reached out to two groups often accused of damaging reefs, tourists and fishermen, and recruited them to help care for the gardens.

For one week a month, the foundation hires local fishermen to work in the coral gardens and on other conservation projects. Fishermen catch an average of 35 pounds of fish per day. By giving these fishermen alternative work, the foundation estimates that it is saving hundreds of pounds of fish per month. The program not only provides fishermen an alternative income source and reduces the local catch; it also allows them to see firsthand why overfishing must be avoided.

Tourists who snorkel or scuba dive can also get involved with the project. A Punta Cana dive shop, Blue Vision, recently developed specialty courses for scuba divers in the handling and care of coral. The courses, which include instruction in the importance of coral ecosystems as well as in specific coral gardening techniques, will allow those certified to work or volunteer in coral gardening programs throughout the world.

While training in coral gardening is available elsewhere, Blue Vision bills its program as the only coral specialty certified by the Professional Association of Dive Instructors (PADI), one of the world’s leading recreational diving and training associations.

Says Mark Goldsmith, a dive instructor at Blue Vision: “The purpose of the course is to train recreational divers and various fisheries managers to become more directly involved in caring for these valuable resources, as traditional conservation techniques are no longer sufficient to stop and reverse their continuing degradation.”

Over the past several years these programs have seen small successes both in preventing and actively combating reef degradation. The foundation hopes to build on that progress by starting a private dive club for coral gardeners and launching training programs for fishermen who want to become tour guides. The program is also experimenting with nurseries for coral species that have yet to be grown in underwater gardens.

“At this point we have the data and the research to show that our techniques work,” says Galván of the Punta Cana Ecological Foundation. “If we haven’t been successful at preserving the species locally, we are on the verge of it.”