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Scientists have discovered that two of the key coral species forming Florida's reef are now ecologically extinct following a intense ocean heatwave caused catastrophic losses.

What 'Functional Extinction' Means

The near-total decline of these corals, which once formed the backbone of reefs in Florida and the Caribbean, means they are no longer able to fulfill their once vital role in constructing and maintaining reef ecosystems that host a variety of marine life.

Functional extinction is a phase before global extinction, a threat that now looms for many coral species.

Scientists this month warned that a critical threshold 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.

Researcher Perspective

"We're running out of time," said Ross Cunning of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and absent immediate, ambitious actions to slow ocean warming and enhance coral survival, we risk the extinction of even more corals from reefs in Florida and around the world."

Details of the New Research

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

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

The two species are complex, reef-building corals and are named because they look like, respectively, the antlers of male deer and elks.

However, scientists who performed diver surveys of over fifty-two thousand colonies of the species, across 391 sites along Florida's coast, found extensive, often devastating, losses.

Regional Effects

• Along the Florida Keys, mortality rates reached ninety-eight percent and even 100%, showing a total eradication of the corals.
• In south-east Florida, where temperatures have been cooler, death rates were reduced, at about thirty-eight percent.

Historical and Present Threats

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

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

The 2023 event caused the ninth episode of bleaching on the Florida reef – a phenomenon whereby corals become thermally stressed and eject the algae partners living in their tissues, causing them to become bleached white.

If temperatures remain elevated, the corals die off entirely.

Global Consequences

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

This presents a major threat to:

• A quarter of all ocean life that relies upon what are essentially the rainforests of the sea.
• Millions of people who rely on corals to support fish that they can eat and gain an income from.

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

Preservation Attempts

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

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

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

Further Researcher Insight

"Elkhorn corals, especially, are some of the key wave-breaking coral species in the area," noted Andrew Baker, a marine biologist at the Miami University.

"They were once common on shallow reef tops in the Caribbean, and if we want our reefs to continue protecting our coastlines from inundation during storms, its worth taking exceptional steps to ensure we don't lose these corals completely."