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

The Meaning Behind 'Functional Extinction' Means

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 fulfill their previously crucial role in building and sustaining reef ecosystems that support a diversity of marine life.

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

Researchers recently alerted that a critical threshold has been crossed, whereby corals globally are likely to be wiped out due to global heating, which is increasing ocean temperatures to unbearable levels.

Researcher Insight

"Time is running out," said Ross Cunning of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity due to climate change, and absent swift, decisive measures to slow ocean warming and boost coral resilience, we risk the disappearance of even more corals from reefs in Florida and worldwide."

The New Research

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

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

The two species are complex, reef-forming corals and are named because they look like, respectively, the horns of stags 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 devastating, losses.

Regional Effects

• In the Florida Keys, death rates reached ninety-eight percent and even 100%, revealing a complete annihilation of the corals.
• In south-east Florida, where temperatures have been cooler, mortality rates were lower, at about 38%.

Past and Present Dangers

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

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

The 2023 event caused the ninth occurrence of coral 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 stay high, the corals die off entirely.

Global Implications

Worldwide, coral reefs are among the ecosystems most at risk to the anthropogenic climate crisis.

This presents a significant danger to:

• One-fourth of all ocean life that relies upon what are essentially the marine rainforests.
• Millions of people who depend upon corals to sustain fish that they can consume and gain an income from.

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

Conservation Attempts

In a desperate attempt to avert a death spiral of endangered corals, scientists have established 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 restore some of the ninety percent 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 absent significant actions, scientists caution.

Additional Expert Commentary

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

"They were once abundant on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from inundation during storms, it is worthwhile taking extraordinary measures to ensure we don't lose these corals completely."