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Researchers have found that two of the most important coral species forming Florida's reef have become functionally extinct after a intense ocean heatwave caused catastrophic losses.

What 'Functional Extinction' Means

The almost complete decline of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they are no longer able to play their once vital role in constructing and maintaining reef ecosystems that host a diversity of marine life.

Ecological extinction is a phase preceding total extinction, a threat that now hangs for many coral species.

Researchers recently alerted that a critical threshold has been crossed, meaning corals around the world are set to be wiped out due to climate change, which is increasing ocean temperatures to unbearable levels.

Expert Perspective

"Time is running out," stated the lead author of the new Florida study. "Extreme heatwaves are becoming more frequent and intense due to climate change, and without swift, decisive measures to slow ocean warming and enhance coral survival, we face the danger of the extinction of even more corals from reefs in Florida and around the world."

The Recent Study

The new research, published in the Science journal, examined the outcome of staghorn coral and elkhorn coral corals off the Florida coast after a severe marine heatwave in 2023.

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

The two species are complex, reef-building corals and are named because they resemble, respectively, the horns of stags and elks.

However, researchers who performed underwater 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, death rates reached 98% and even 100%, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been lower, mortality rates were lower, at about 38%.

Past and Present Dangers

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

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

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

If temperatures remain elevated, the corals die off completely.

Global Implications

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

This presents a major threat to:

• One-fourth of all ocean life that relies upon what are effectively the marine rainforests.
• Hundreds of millions of people who depend upon corals to sustain fish that they can eat and earn a livelihood from.

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

Preservation Attempts

In a last-ditch effort to prevent a decline of endangered corals, scientists have created repositories of Acropora in marine facilities and ocean-based nurseries.

Efforts have been undertaken to reseed corals on reefs in Florida, as well, in an effort to restore some of the 90% of coral cover disappeared off the state in the last forty years.

But as global heating continues to escalate, there is little hope of continued existence of these species without significant actions, scientists caution.

Further Expert Commentary

"Elkhorn species, in particular, are some of the most important wave-breaking coral species in the region," noted a study co-author, a marine biologist at the Miami University.

"They used to be common on shallow reef tops in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from inundation during storms, its worth taking extraordinary measures to ensure we don't lose these corals altogether."