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Researchers have found that two of the most important coral species forming Florida's reef are now ecologically extinct following a intense ocean heatwave caused catastrophic losses.

What 'Functional Extinction' Means

The almost complete decline of these corals, which once formed the foundation of reefs in Florida and the Caribbean, means they can no longer play their previously crucial role in building and sustaining reef ecosystems that host a variety of marine life.

Functional extinction is a phase preceding global extinction, a threat that now hangs for many coral species.

Scientists this month alerted that a tipping point has been crossed, meaning corals globally 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 Ross Cunning of the new Florida study. "Extreme heatwaves are becoming more frequent and intense due to global warming, and absent swift, decisive measures to reduce ocean heating and boost coral resilience, we risk the disappearance of even more corals from reefs in Florida and around the world."

The New Research

The recent study, featured in the Science journal, examined the fate of staghorn and elkhorn corals off the Florida coast after a intense 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-forming corals and are identified because they resemble, in turn, the horns of male deer and elks.

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

Regional Effects

• In the Florida Keys, death rates reached 98% and even 100%, showing a total eradication of the corals.
• In southeastern 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 many years of regional pressures in Florida, such as contaminated water from pollutants that run off the land, as well as disease.

But the 2023 marine heatwave has proved fatal for these temperature-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 expel the symbiotic algae living in their tissues, causing them to become ghostly white.

If temperatures remain elevated, the corals die off entirely.

Worldwide Implications

Worldwide, coral reefs are among the ecosystems most vulnerable to the anthropogenic climate emergency.

This presents a significant danger 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 support fish that they can eat and earn a livelihood from.

Corals also act as a protective barrier to safeguard our shorelines from powerful storms, which are themselves being worsened by increasing global heat.

Conservation Attempts

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

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

But as global heating continues to intensify, there is slim chance of continued existence of these species absent major interventions, scientists caution.

Further Expert Commentary

"Elkhorn species, especially, are some of the key wave-breaking coral species in the area," said a study co-author, 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 keep safeguarding our coastlines from flooding during storms, its worth taking extraordinary measures to ensure we don't lose these corals completely."