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Researchers have found that two of the primary coral species comprising Florida's reef have become ecologically extinct after a intense ocean heatwave caused devastating losses.

The Meaning Behind 'Functional Extinction' Signifies

The almost complete collapse of these corals, which once formed the backbone of reefs in Florida and the Caribbean, indicates they are no longer able to fulfill their once vital role in constructing and maintaining reef ecosystems that support a variety of marine life.

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

Researchers this month alerted that a critical threshold had been reached, meaning corals around the world are set to be wiped out due to climate change, which is raising ocean temperatures to intolerable levels.

Expert Insight

"We're running out of time," stated Ross Cunning of the new Florida study. "Severe marine heatwaves are increasing in frequency and severity 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 worldwide."

The New Research

The recent study, featured in the Science journal, analyzed the outcome of staghorn and elkhorn corals off the Florida coast following a intense marine heatwave in 2023.

This event raised temperatures on Florida's fraying coral reefs to their peak temperatures in over 150 years.

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

However, researchers who performed underwater surveys of over fifty-two thousand colonies of the species, across nearly four hundred sites along Florida's coast, found widespread, often catastrophic, losses.

Regional Effects

• In the Florida Keys, death rates reached 98% and even 100%, showing a complete annihilation of the corals.
• In southeastern Florida, where temperatures have been lower, mortality rates were lower, at about 38%.

Past and Present Dangers

The two Acropora species had already suffered 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 heatwave has proved fatal for these heat-sensitive species.

The 2023 heat event caused the ninth episode of 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 bleached white.

If temperatures stay high, the corals perish entirely.

Worldwide Consequences

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

This poses a significant danger to:

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

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

Conservation Efforts

In a desperate attempt to avert a death spiral of endangered corals, scientists have created collections of Acropora in aquariums and ocean-based nurseries.

Attempts have been undertaken to reseed corals on reefs in Florida, as well, in an effort to restore some of the 90% of coral cover disappeared off the state in the past four decades.

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

Additional Researcher Insight

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

"They were once abundant on shallow reef tops in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from flooding during storms, it is worthwhile taking exceptional steps to ensure we preserve these corals completely."