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Scientists have discovered that two of the key coral species comprising Florida's reef have become functionally extinct following a intense ocean heatwave led to 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, indicates they are no longer able to play their once vital role in building and sustaining reef ecosystems that host a variety of marine life.

Ecological extinction is a phase preceding total extinction, a danger that now looms for many coral species.

Scientists this month alerted that a tipping point has been crossed, whereby corals globally are set to be eradicated due to climate change, which is increasing ocean temperatures to intolerable levels.

Expert Perspective

"We're running out of time," said the lead author of the recent research. "Severe marine heatwaves are becoming more frequent and intense due to climate change, and absent immediate, ambitious actions to reduce ocean heating and boost coral resilience, we face the danger of the disappearance of even more corals from reefs in Florida and worldwide."

Details of the Recent Study

The new research, featured in the journal Science, analyzed 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 highest levels in over 150 years.

The two species are intricate, reef-forming corals and are identified because they look like, respectively, the antlers of stags and elks.

However, scientists who performed diver surveys of more than 52,000 colonies of the species, across nearly four hundred sites along Florida's coast, found widespread, often catastrophic, losses.

Regional Impact

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

Historical and Present Dangers

The two Acropora species had already endured from decades of localized impacts in Florida, such as contaminated water from pollutants that wash off the land, as well as disease.

But the 2023 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 algae partners living in their tissues, causing them to become ghostly white.

If temperatures remain elevated, the corals perish entirely.

Global Implications

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

This presents a significant danger to:

• A quarter of all ocean life that depends on what are effectively the marine rainforests.
• Hundreds of millions of people who rely on corals to sustain fish that they can consume and gain an income from.

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

Conservation Attempts

In a last-ditch effort to avert a death spiral of endangered corals, scientists have established repositories of Acropora in aquariums and offshore coral nurseries.

Efforts have been made to replant corals on reefs in Florida, too, in an effort to regain some of the 90% of coral cover disappeared off the state in the past four decades.

But as global heating continues to intensify, there is little hope of long-term survival of these species without major interventions, scientists caution.

Further Researcher Insight

"Elkhorn corals, in particular, are some of the most important wave-dampening coral species in the area," said a study co-author, a marine biologist at the University of Miami.

"They were once common on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, its worth taking exceptional steps to ensure we preserve these corals completely."