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

What 'Functional Extinction' Signifies

The near-total collapse of these corals, which once formed the foundation of reefs in Florida and the Caribbean, means they can no longer fulfill their previously crucial role in building and sustaining reef ecosystems that host a variety of marine life.

Functional extinction is a phase preceding total extinction, a threat that now looms for many coral species.

Scientists this month alerted that a tipping point had been reached, meaning corals around the world are set to be wiped out due to global heating, which is increasing ocean temperatures to unbearable levels.

Expert Perspective

"We're running out of time," said the lead author of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and absent swift, decisive measures to slow ocean warming and enhance coral survival, we face the danger of the disappearance of additional coral species from reefs in Florida and worldwide."

The New Research

The recent study, featured in the Science journal, examined the fate of staghorn and elkhorn coral 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 complex, reef-building corals and are identified because they look like, in turn, the antlers of male deer and elks.

However, scientists 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 Impact

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

Historical and Current Threats

The two Acropora species had already suffered from decades of regional pressures in Florida, such as contaminated water from contaminants that run off the land, as well as illness.

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

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

If temperatures stay high, the corals perish completely.

Worldwide Consequences

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.
• Hundreds of 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 safeguard our shorelines from powerful storms, which are themselves being intensified by increasing global heat.

Conservation Efforts

In a last-ditch effort to prevent a death spiral of endangered corals, scientists have created collections of Acropora in aquariums and ocean-based nurseries.

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

But as global heating continues to escalate, there is little hope of long-term survival of these species absent significant actions, researchers warn.

Additional Researcher Insight

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

"They used to be common on shallow reef tops 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 altogether."