The two sites appear to be among the hardest hit. But throughout Florida's reef, which stretches some 350 miles, scientists and advocates are doing triage.
First priority has been salvaging samples of the most threatened species of coral. Before the marine heat wave, there were only about 150 genetic individuals of elkhorn and 300 of staghorn left in the state. (Coral can reproduce asexually, making clones of themselves, so separate corals can have the same genes.)
Divers fanned out across the reef and offshore nurseries, collecting two fragments of each genetic individual. Those were taken to tanks in holding facilities, then loaded onto trailers and driven to two separate locations that will serve as gene banks.
It's a "last-ditch sort of insurance policy," said Jennifer Moore, who is leading the banking effort and coordinates protected coral recovery for NOAA Fisheries' Southeast region. "God forbid everything dies in the water, we still have not lost those individuals."
Coral reefs occur in less than 1 percent of the ocean, but about 25 percent of all marine life depends on them at some point, including fish that provide a critical source of protein to millions of people.
Reefs also protect shorelines from storms, breaking the energy of waves by an average of 97 percent, researchers have found. Worldwide, the goods and services provided by reefs have been valued at $2.7 trillion a year.
Yet they are imperiled. In 2018, the UN scientific panel on climate change noted that the fate of coral reefs hangs in the balance between a global temperature increase of 1.5 degrees Celsius and a rise of 2 degrees Celsius.
The smaller figure would cause further declines of 70 to 90 percent, the scientists said. The larger one would bring losses of more than 99 percent.
While migration can help animals and plants adapt to a warming planet, coral reefs require very specific ocean conditions and take decades, centuries or millenniums to build.
The pace of climate change is too fast, Phanor Montoya-Maya, a marine biologist with the Coral Restoration Foundation, said. Without drastic reductions in greenhouse gas emissions, the world is on track to warm 2.1 to 2.9 degrees by 2100, according to the United Nations.
Stressed corals bleach, meaning they expel the algae that give them color and nourishment. If conditions don't improve, or if bleaching happens too frequently, the corals will die.