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

What 'Functional Extinction' Means

The near-total decline of these corals, which once served as the backbone of reefs in Florida and the Caribbean, indicates they are no longer able to play their previously crucial role in constructing and maintaining reef ecosystems that support a diversity of marine life.

Functional extinction is a phase before global extinction, a danger that now hangs for many coral species.

Scientists recently alerted that a critical threshold has been crossed, meaning corals globally are set to be eradicated due to global heating, which is raising ocean temperatures to intolerable levels.

Researcher Insight

"Time is running out," stated the lead author of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity due to global warming, and without immediate, ambitious actions to reduce ocean heating and boost coral resilience, we risk the extinction of additional coral species from reefs in Florida and worldwide."

The Recent Study

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

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

The two species are intricate, reef-forming corals and are named because they resemble, in turn, the horns of male deer and elk.

However, researchers 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.

Geographic Effects

• Along 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 lower, mortality rates were reduced, at about thirty-eight percent.

Past and Current Threats

The two Acropora species had already suffered from decades of localized impacts in Florida, such as poor water quality from pollutants that run 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 episode of coral bleaching on the Florida reef – a phenomenon whereby corals become thermally stressed and expel the algae partners living in their tissues, causing them to become ghostly white.

If temperatures remain elevated, the corals die off completely.

Global Implications

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

This presents a significant danger to:

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

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

Preservation Efforts

In a last-ditch effort to avert a death spiral of threatened corals, scientists have established collections of Acropora in marine facilities and ocean-based nurseries.

Attempts have been made to replant corals on reefs in Florida, too, in an effort to regain some of the 90% of coral cover lost off the state in the last forty years.

But as climate change continues to escalate, there is slim chance of long-term survival of these species absent significant actions, scientists caution.

Additional Researcher Insight

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

"They used to be common on shallow reef crests in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, it is worthwhile taking extraordinary measures to ensure we don't lose these corals completely."