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

The Meaning Behind 'Functional Extinction' Signifies

The almost complete decline of these corals, which once served as the foundation of reefs in Florida and the Caribbean, indicates they can no longer play their once vital role in constructing and maintaining 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, whereby corals globally are likely to be eradicated due to climate change, which is increasing ocean temperatures to unbearable levels.

Researcher Perspective

"Time is running out," said the lead author of the new Florida study. "Extreme heatwaves are increasing in frequency and severity due to climate change, and without swift, decisive measures to slow ocean warming and boost coral resilience, we face the danger of the extinction of even more corals from reefs in Florida and worldwide."

Details of the Recent Study

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

This event raised temperatures on Florida's deteriorating coral reefs to their peak temperatures in over 150 years.

The two species are intricate, reef-building corals and are named because they look like, in turn, the antlers of male deer and elk.

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

Geographic Effects

• In the Florida Keys, mortality rates hit 98% and even 100%, revealing a total eradication of the corals.
• In south-east Florida, where temperatures have been lower, mortality rates were lower, at about 38%.

Historical and Current Dangers

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

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

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

If temperatures remain elevated, the corals perish entirely.

Global Implications

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

This presents a major threat to:

• A quarter of all ocean life that relies upon what are effectively the rainforests of the sea.
• Millions of people who depend upon corals to support fish that they can consume and gain an income from.

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

Conservation Efforts

In a desperate attempt to avert a death spiral of threatened corals, scientists have established collections of Acropora in aquariums and ocean-based nurseries.

Attempts have been made to replant corals on reefs in Florida, as well, in an effort to restore some of the ninety percent of coral cover disappeared off the state in the past four decades.

But as global heating continues to escalate, there is slim chance of long-term survival of these species without major interventions, scientists caution.

Additional Expert Commentary

"Elkhorn species, in particular, are some of the most important wave-breaking coral species in the area," noted Andrew Baker, a ocean scientist at the Miami University.

"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, it is worthwhile taking exceptional steps to ensure we don't lose these corals altogether."