When Hurricane Delta hit Puerto Morelos, Mexico, in October, the Brigade waited anxiously for the sea to quiet. The group, an assortment of tour guides, diving instructors, park rangers, fishermen and researchers, needed to get in the water as soon as possible. The coral reef that protects their town — an undersea forest of living limestone branches that blunted the storm's destructive power — had taken a beating.

Now it was their turn to help the reef, and they didn't have much time.

"We're like paramedics," said María del Carmen García Rivas, director of the national park that manages the reef and a leader of the Brigade. When broken corals roll around and get buried in the sand, they soon die. But pieces can be saved if they are fastened back onto the reef.

"The more days that pass, the less chance they have of survival," she said.

The race to repair the reef is more than an ecological fight; it's also a radical experiment in finance. The reef could be the first natural structure with its own insurance policy, according to environmental groups and insurance companies. And Hurricane Delta's force triggered the first payout — about $850,000 to be used for the reef's repairs. The success or failure of this experiment could determine whether communities around the world start using a new tool that marries nature and finance to protect against the effects of climate change.

When the Brigade laid eyes on their reef, which runs 17 miles south of Cancún and is home to critically endangered elkhorn coral, it looked ransacked. Structures the size of bathtubs were flipped upside down. Coral stalks lay like felled trees. Fragments of broken coral coated the seafloor.

On the boat, cement mixers prepared a paste that snorkelers ferried down to divers who spent hours fastening pieces back on the reef. At the end of a grueling day, Tamara Adame, a diving instructor and guide, wondered whether the tiny team could make a dent. "Is it actually going to make a difference that I'm here all day picking up the pieces?" she asked herself.

Just as a house is insured against fire, or a car against crashes, last year a 103-mile stretch of the coast, including the reef, was insured against hurricanes with a wind speed of 115 mph or greater. It didn't take long for the policy to pay off: Hurricane Delta slammed into the reef in October.

Ideally, reefs wouldn't need such interventions. After all, they've been surviving hurricanes for millennia. But rising sea temperatures, ocean acidification, sewage pollution and overfishing leave coral more vulnerable to hurricane damage. And hurricanes themselves are becoming more severe.

Environmentalists and insurance companies behind it hope it becomes a model for protecting other coastlines, insuring mangroves, salt marshes and other natural barriers to storms. These nature-based defenses protect coastal properties and biodiversity all at once.

"Having this insurance policy is really like water in the desert," said Efraín Villanueva Arcos, the environment secretary for Quintana Roo.

Some scientists and environmentalists protest that the policy diverts money to private companies that could instead be spent directly to protect the local people and environment. It can't address longer-term threats from climate change.

But "if we want to move the needle on how we are impacting nature," said Fernando Secaira, a specialist on climate risk and resilience at the Nature Conservancy, "we need to move into economic terms."