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Scientists have discovered that two of the key coral species comprising Florida's reef are now ecologically extinct after a withering ocean heatwave caused devastating losses.

What 'Functional Extinction' Means

The almost complete decline of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they can no longer fulfill their once vital role in building and sustaining reef ecosystems that host a variety of marine life.

Functional extinction is a stage preceding global extinction, a threat that now looms for many coral species.

Researchers recently alerted that a tipping point had been reached, whereby corals around the world are likely to be eradicated due to global heating, which is raising ocean temperatures to unbearable levels.

Expert Perspective

"Time is running out," said Ross Cunning of the recent research. "Severe marine heatwaves are becoming more frequent and intense due to climate change, and without immediate, ambitious actions to slow ocean warming and boost coral resilience, we face the danger of the disappearance of even more corals from reefs in Florida and around the world."

Details of the Recent Study

The new research, featured in the Science journal, analyzed the fate of staghorn coral and elkhorn corals off the Florida coast after a severe marine heatwave in 2023.

This event elevated temperatures on Florida's deteriorating coral reefs to their highest levels in more than a century and a half.

The two species are complex, reef-forming corals and are identified because they look like, respectively, the horns of male deer and elks.

However, scientists who conducted underwater surveys of more than 52,000 colonies of the species, across 391 sites along Florida's coast, found widespread, often catastrophic, losses.

Geographic Effects

• In the Florida Keys, mortality rates hit ninety-eight percent and even 100%, showing a complete annihilation of the corals.
• In southeastern Florida, where temperatures have been cooler, mortality rates were lower, at about thirty-eight percent.

Historical and Present Dangers

The two Acropora species had already endured from decades of localized impacts in Florida, such as contaminated water from contaminants that run off the land, as well as illness.

But the 2023 marine heatwave has proved lethal for these temperature-sensitive species.

The 2023 event caused the ninth occurrence of coral bleaching on the Florida reef – a phenomenon whereby corals become thermally stressed and expel the symbiotic algae living in their tissues, causing them to become bleached white.

If temperatures remain elevated, the corals perish completely.

Worldwide Consequences

Globally, coral reefs are among the ecosystems most at risk to the human-caused climate crisis.

This poses a major threat to:

• One-fourth of all ocean life that relies upon what are essentially the rainforests of the sea.
• Millions of people who rely on corals to support fish that they can consume and gain an income from.

Corals also serve as a barrier to protect our shorelines from powerful storms, which are themselves being worsened by increasing global heat.

Preservation Attempts

In a last-ditch effort to avert a death spiral of threatened corals, scientists have created collections of Acropora in aquariums and ocean-based nurseries.

Efforts have been made to replant corals on reefs in Florida, as well, in an effort to regain some of the 90% of coral cover disappeared off the state in the last forty years.

But as global heating continues to escalate, there is little hope of continued existence of these species absent significant actions, scientists caution.

Additional Expert Commentary

"Elkhorn species, in particular, are some of the most important wave-dampening coral species in the area," said a study co-author, a marine biologist at the University of Miami.

"They used to be abundant on shallow reef crests in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from inundation during storms, it is worthwhile taking extraordinary measures to ensure we preserve these corals altogether."