When researchers returned to coral reefs off the Florida Keys, they expected to document damage. What caught them off guard was what wasn't there.

What's happening?

During the summer of 2023, unusually hot ocean temperatures lingered off South Florida, triggering a severe marine heat wave that proved fatal for endangered elkhorn and staghorn corals, according to an article from Florida International University on Phys.org.

Once home to dense, branching corals teeming with fish, parts of the reef now resemble a barren seafloor. Scientists say the loss is so complete that when FIU researchers revisited long-studied reef sites, they found mass die-offs — coral formations that no longer exist. 

"The elkhorn coral is really beautiful, it's iconic," FIU research scientist Kathryn Lesneski said in the article. But when her team returned to document the reefs, the structures they once photographed were gone. "The size and extent of the corals … just don't exist anymore," she said.

Why is this concerning?

Elkhorn and staghorn corals act like the scaffolding of reef ecosystems. Their complex shapes provide shelter for fish, absorb wave energy before it hits shore, and help protect coastal communities from flooding and erosion.

"To protect our coastal communities, we have historically relied on that natural reef structure," Lesneski explained in the article.

As reefs disappear, fish lose shelter, and coastlines lose protection. Storm surge reaches farther inland, and communities that rely on fishing and tourism start to feel the strain. Replacing that natural barrier often means expensive seawalls and other engineered fixes that few towns want — or can afford.

Similar threats are playing out elsewhere, including federally protected reefs like Flower Garden Banks, where industrial pressure and warming waters are putting rare coral ecosystems at risk.

What's being done about it?

There's no single fix for what researchers are seeing on Florida's reefs, but scientists are trying several approaches at once. Some teams are testing whether certain coral strains can better withstand higher temperatures than others. Others are growing corals in underwater nurseries, then transplanting them back onto damaged reef sites — a slow process with no guarantee of success.

In Florida, researchers are also studying unlikely helpers. Recent work suggests Caribbean king crabs may play a role in reef recovery by eating back fast-growing algae that can overwhelm young corals before they have a chance to establish themselves.

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Local actions matter too, especially as reefs struggle to recover. Cleaner coastal water reduces stress on corals already pushed to their limits. Careful boating helps prevent physical damage to fragile reef structures. Even small choices, like using reef-safe sunscreen, can reduce chemical exposure in shallow reef areas.

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