As South Florida's ritzy coastline, bejeweled with luxury condos and posh hotels, has come under increasing threats from flooding and storm surge driven by climate change, scientists have focused on reefs to defend that wealth.
Now, for the first time, government researchers have come up with a price for the protection: $657 million annually between Fort Lauderdale and Miami alone. It rises to as much as $1.6 billion during a severe storm.
Across the U.S., the study found reefs provide $1.8 billion in protection annually for Puerto Rico, Hawaii and other U.S. shorelines. They also protect more than 18,000 people from flooding.
"This very specifically is saying these reefs protect this many people, this much value in buildings and this value in economic activity," said USGS geologist and lead author Curt Storlazzi. "This is a big game changer because the U.S. spends something like a half billion dollars a year on hazard risk reduction. And I think we spend a million or two on ecosystem restoration."
The findings also come at a critical time for coral.
In South Florida, a mysterious disease started in 2014 off Virginia Key and has so far spread past Key West. It now stands as the longest and largest infection of coral anywhere in the world.
An emergency response team overseen by the National Oceanic and Atmospheric Administration is racing to come up with a treatment plan. They're also collecting corals from outside diseased areas and sending them to coral labs - the University of Miami received more than 300 this week - to build a Noah's Ark for dying coral.
Globally, a three-year bleaching event that ended in 2017 has also devastated reefs. By some estimates, 30 percent of coral on the planet's reefs died.
For this study, called "Rigorously Valuing the Role of U.S. Coral Reefs in Coastal Hazard Risk Reduction," USGS researchers looked at the amount of reefs lost due to erosion and disease over the years. It amounts to as much as three feet in some places.
The team of 10 lead scientists modelled the difference in flooding during 10, 50, 100 and and 500-year flooding events before and after the erosion. These storms happen infrequently, but are projected to increase on a warming planet.
"You might have two 100-year events in 20 years," Storlazzi said. "It's just the probability of it happening in a year is like flipping a coin."
They then calculated potential dollars lost by looking at the value of property and economic activity. Because of improved computer modeling, they were able to scale the study at a very fine level, calculating value and loss in 33-by-33 feet grids for the first time.
"So we've done a national scale project at a local scale decision-making resolution," Storlazzi said.
The researchers are also looking reefs damaged by hurricanes Irma and Maria to calculate the dollar value of increased hazards because of the lost protection. They're also looking at projected losses of reefs to figure out future costs.
"On the flip side, to give some hope out there, we're also modeling how theoretical reef restoration could reduce those coastal hazards," Storlazzi said.
By putting a dollar value on reef protection, managers can better evaluate the most effective ways to protect shorelines, particularly the U.S. Army Corps of Engineers, he said.
The U.S. Department of Defense paid for part of the study, a sign of the growing role of natural defenses to handle hazards on a warming planet. For example, in 2016 scientists argued restoring the Everglades could also fight climate change when they concluded that mangroves provide between $2 billion and $3.4 billion in relief by absorbing and storing carbon.
"With this, we can show that [reefs] protect people and lives and infrastructure," Storlazzi said. "Some people might not care about ecosystem services and things like that, but I think people can understand coastal protection."