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Scientists have discovered that two of the primary coral species comprising Florida's reef are now functionally extinct following a withering ocean heatwave led to devastating losses.

The Meaning Behind 'Functional Extinction' Means

The almost complete collapse of these corals, which once served as the backbone of reefs in Florida and the Caribbean, means they are no longer able to play their once vital role in building and sustaining reef ecosystems that support a variety of marine life.

Ecological extinction is a stage before global extinction, a threat that now hangs for many coral species.

Researchers recently warned that a critical threshold has been crossed, whereby corals globally are set to be eradicated due to global heating, which is increasing ocean temperatures to intolerable levels.

Researcher Perspective

"Time is running out," stated the lead author of the recent research. "Severe marine heatwaves are increasing in frequency and severity due to climate change, and without swift, decisive measures to reduce ocean heating and enhance coral survival, we risk the extinction of additional coral species from reefs in Florida and around the world."

The New Research

The new research, featured in the Science journal, examined the fate of staghorn coral and elkhorn corals off the Florida coast following 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, in turn, the horns of stags and elks.

However, researchers who performed underwater surveys of over fifty-two thousand colonies of the species, across nearly four hundred sites along Florida's coast, found extensive, often catastrophic, losses.

Regional Impact

• In the Florida Keys, mortality rates hit ninety-eight percent and even 100%, showing a complete annihilation of the corals.
• In south-east Florida, where temperatures have been cooler, death rates were reduced, at about 38%.

Past and Present Threats

The two Acropora species had already suffered from many years of localized impacts in Florida, such as poor water quality from pollutants that run off the land, as well as disease.

But the 2023 heatwave has been lethal for these heat-sensitive species.

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

If temperatures remain elevated, the corals die off entirely.

Worldwide Implications

Globally, coral reefs are among the ecosystems most vulnerable to the human-caused climate emergency.

This poses a major threat to:

• A quarter of all ocean life that depends on what are effectively the marine rainforests.
• Hundreds of millions of people who rely on corals to sustain fish that they can consume and earn a livelihood from.

Corals also serve as a protective barrier to protect our shorelines from intense hurricanes, which are themselves being worsened by rising global temperatures.

Conservation Attempts

In a desperate attempt to avert a death spiral of endangered corals, scientists have created collections of Acropora in marine facilities and ocean-based nurseries.

Attempts have been undertaken to reseed corals on reefs in Florida, too, in an effort to restore some of the 90% of coral cover lost off the state in the last forty years.

But as climate change continues to escalate, there is little hope of continued existence of these species absent major interventions, scientists caution.

Further Researcher Insight

"Elkhorn species, especially, are some of the most important wave-dampening coral species in the region," 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 continue protecting our coastlines from flooding during storms, its worth taking exceptional steps to ensure we don't lose these corals altogether."