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Scientists have discovered that two of the primary coral species forming Florida's reef have become functionally extinct after a withering ocean heatwave caused devastating losses.

What 'Functional Extinction' Signifies

The near-total decline of these corals, which once formed the foundation of reefs in Florida and the Caribbean, indicates they are no longer able to fulfill their previously crucial role in building and sustaining reef ecosystems that support a variety of marine life.

Functional extinction is a stage before global extinction, a danger that now looms for many coral species.

Scientists this month warned that a critical threshold had been reached, meaning corals globally are likely to be wiped out due to climate change, which is raising ocean temperatures to unbearable levels.

Expert Perspective

"Time is running out," said the lead author 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 risk the extinction of even more corals from reefs in Florida and worldwide."

Details of the New Research

The recent study, featured in the Science journal, analyzed the outcome of staghorn 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 intricate, reef-building corals and are identified because they look like, in turn, the horns of stags and elks.

However, scientists who performed diver surveys of over fifty-two thousand colonies of the species, across 391 sites along Florida's coast, found widespread, often catastrophic, losses.

Geographic Impact

• Along the Florida Keys, mortality rates reached ninety-eight percent and even one hundred percent, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been lower, death rates were lower, at about 38%.

Historical and Present Threats

The two Acropora species had already suffered from decades of regional pressures in Florida, such as contaminated water from pollutants that run off the land, as well as disease.

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

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

If temperatures remain elevated, the corals perish completely.

Global Consequences

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

This poses a major threat to:

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

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

Preservation Efforts

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

Attempts have been made to replant corals on reefs in Florida, too, in an effort to restore some of the 90% of coral cover disappeared off the state in the past four decades.

But as climate change continues to escalate, there is slim chance of continued existence of these species absent significant actions, researchers warn.

Further Researcher Insight

"Elkhorn species, especially, are some of the key wave-dampening coral species in the region," said a study co-author, a ocean scientist at the University of Miami.

"They were once common 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 completely."