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Scientists have discovered that two of the most important coral species forming Florida's reef have become functionally extinct after a withering ocean heatwave led to catastrophic losses.

The Meaning Behind 'Functional Extinction' Signifies

The near-total collapse of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they can no longer play their once vital role in building and sustaining reef ecosystems that support a diversity of marine life.

Functional extinction is a phase preceding global extinction, a danger that now looms for many coral species.

Researchers this month warned that a critical threshold had been reached, meaning corals around the world are set to be wiped out due to climate change, which is increasing ocean temperatures to intolerable levels.

Expert Insight

"Time is running out," said Ross Cunning of the new Florida study. "Extreme heatwaves are becoming more frequent and intense due to climate change, and absent immediate, ambitious actions to slow ocean warming and enhance coral survival, we face the danger of the extinction of even more corals from reefs in Florida and worldwide."

Details of the New Research

The new research, featured in the journal Science, examined the outcome of staghorn and elkhorn corals off the Florida coast following a intense marine heatwave in 2023.

This event elevated temperatures on Florida's fraying coral reefs to their highest levels in over 150 years.

The two species are intricate, reef-building corals and are named because they resemble, respectively, the antlers of stags 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

• Along the Florida Keys, mortality rates hit 98% and even 100%, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been cooler, mortality rates were reduced, at about thirty-eight percent.

Historical and Present Dangers

The two Acropora species had already suffered from many years of regional pressures in Florida, such as contaminated water from contaminants that wash off the land, as well as disease.

But the 2023 heatwave has proved fatal for these heat-sensitive species.

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

If temperatures stay high, the corals die off completely.

Global Implications

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

This poses a significant danger to:

• A quarter of all ocean life that depends on what are essentially the rainforests of the sea.
• Hundreds of millions of people who depend upon corals to support fish that they can eat and earn a livelihood from.

Corals also act as a protective barrier to protect our shorelines from intense hurricanes, which are themselves being intensified by increasing global heat.

Conservation Efforts

In a last-ditch effort to prevent a death spiral of threatened corals, scientists have established repositories of Acropora in marine facilities and offshore coral 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 lost off the state in the past four decades.

But as climate change continues to intensify, there is slim chance of continued existence of these species without significant actions, researchers warn.

Further Researcher Insight

"Elkhorn species, in particular, are some of the key wave-breaking coral species in the region," said Andrew Baker, a marine biologist at the University of Miami.

"They used to be common 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 exceptional steps to ensure we don't lose these corals altogether."