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Scientists have discovered that two of the key coral species comprising Florida's reef have become ecologically extinct following a withering ocean heatwave led to catastrophic losses.

What 'Functional Extinction' Signifies

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

Functional extinction is a phase before total extinction, a danger that now looms for many coral species.

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

Researcher Perspective

"We're running out of time," stated the lead author of the recent research. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and without swift, decisive measures to reduce ocean heating and enhance coral survival, we risk the disappearance of even more corals from reefs in Florida and worldwide."

Details of the New Research

The recent study, featured in the journal Science, examined the outcome of staghorn and elkhorn corals off the Florida coast after a severe marine heatwave in 2023.

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

The two species are intricate, reef-building corals and are named because they resemble, respectively, the horns of male deer and elk.

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

Geographic Effects

• In 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 cooler, mortality rates were reduced, at about 38%.

Historical and Present Dangers

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

But the 2023 heatwave has proved 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 bleached white.

If temperatures remain elevated, the corals die off completely.

Worldwide Consequences

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

This poses a major threat to:

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

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

Preservation Attempts

In a desperate attempt to avert a death spiral of threatened corals, scientists have created repositories of Acropora in marine facilities and offshore coral nurseries.

Efforts have been undertaken to replant corals on reefs in Florida, too, in an effort to regain 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 without significant actions, researchers warn.

Additional 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 were once common on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, it is worthwhile taking exceptional steps to ensure we preserve these corals altogether."