In a hurricane-proof lab miles down the Florida Keys, scientists coddle tiny pieces of coral from the moment they are spawned until they are just hearty enough to be separated into specimens equipped to survive in the wild.

Then these dark-green fragments are put through misery, plunged into tanks mimicking the hotter, more acidic waters projected to one day overtake the region. Many will die, but those that endure the hostile testing will be painstakingly transplanted back in the Atlantic.

For generations, marine biologists working around the 360-mile coral reef made sure their research didn’t disturb the fragile kaleidoscope of marine habitat so critical to the ecosystem and a multibillion-dollar tourist economy.

But as global warming brings the natural wonder to the brink of extermination, scientists are abandoning their hands-off approach in favor of a once-unthinkable strategy: manipulating the natural balance of the reef.

The work is pioneering, and some say unsettling. And it is being watched closely by entrepreneurs and technologists, who see opportunity in this effort to bring what scientists call “assisted evolution” to the wild.

On Summerland Key, an army of scientists is trying to rebuild thousands of square acres of the reef one centimeter at a time, cutting tens of thousands of coral microfragments, toughening them in the lab and replanting them in the ocean, piece by piece.

At the nonprofit Coral Restoration Foundation in Key Largo, divers delicately hang corals on rows of “trees” constructed of plastic pipe in an underwater nursery, where they nourish themselves until they are ready to be replanted.

Both efforts are part of a laborious, costly international experiment that researchers say offers the only hope for warding off total devastation of reef systems worldwide that provide the primary source of food to as many as a billion people and a home to one quarter of all marine species at some point in their lives.

“We have no choice now,” said Michael Crosby, chief executive of Mote Marine Laboratory, which runs the 19,000-square-foot lab on Summerland Key. “These coral are not able to come back on their own. They are really sliding into functional extinction.”

About 95 percent of the coral on the Florida Reef Tract has already died.

It’s a familiar cliché in areas where coral is on life-support: The reefs are the canary in the coal mine of climate change. This is not about projections of what might come if emissions continue unabated. The havoc is already here.

“We are not so naive to think we can restore every coral that was ever lost,” said Jessica Levy, a the reef restoration program manager at the Key Largo foundation. “Our goal is to keep that material out there, push it and make things as best as we can, to promote natural recovery.”

Scientists are trying to keep the coral alive long enough to buy time for governments to solve the root problem: climate change.

There have been encouraging breakthroughs. Growing a piece of reef the size of a basketball, which takes 25 to 100 years in the wild, can now be done in as few as three years.

“We are looking at a potential complete ecosystem loss, which to my knowledge has not happened in human history,” Levy said. “I don’t think anyone wants to be responsible for that occurring.”