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Researchers have found that two of the key coral species forming Florida's reef are now functionally extinct following a intense ocean heatwave led to devastating losses.

What 'Functional Extinction' Signifies

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

Functional extinction is a phase preceding total extinction, a danger that now hangs for many coral species.

Researchers this month warned that a critical threshold has been crossed, whereby corals globally 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. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and without swift, decisive measures to slow ocean warming and boost coral resilience, we risk the disappearance of even more corals from reefs in Florida and around the world."

The New Research

The new research, featured in the Science journal, analyzed the fate of staghorn coral and elkhorn coral corals off the Florida coast following a severe marine heatwave in 2023.

This event elevated temperatures on Florida's fraying coral reefs to their peak temperatures 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 male deer and elks.

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

Geographic Effects

• Along the Florida Keys, mortality rates hit 98% and even one hundred percent, showing a total eradication of the corals.
• In southeastern Florida, where temperatures have been cooler, death rates were lower, at about 38%.

Past and Present Threats

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

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

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

If temperatures remain elevated, the corals perish completely.

Global Consequences

Worldwide, coral reefs are among the ecosystems most at risk 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.
• Millions of people who depend upon corals to sustain fish that they can eat and earn a livelihood from.

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

Conservation Efforts

In a last-ditch effort to avert a decline of threatened corals, scientists have created collections of Acropora in aquariums and offshore coral nurseries.

Efforts have been made to reseed corals on reefs in Florida, as well, in an effort to restore some of the 90% of coral cover lost off the state in the past four decades.

But as global heating continues to escalate, there is slim chance of continued existence of these species without major interventions, scientists caution.

Additional Researcher Insight

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

"They used to be abundant 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 don't lose these corals altogether."