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Scientists have discovered that two of the key coral species forming Florida's reef have become ecologically extinct after a withering ocean heatwave caused devastating losses.

The Meaning Behind 'Functional Extinction' Signifies

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

Functional extinction is a stage before total extinction, a threat that now hangs for many coral species.

Researchers recently warned that a critical threshold had been reached, meaning corals globally are likely to be eradicated due to global heating, which is increasing ocean temperatures to unbearable levels.

Researcher Insight

"Time is running out," stated Ross Cunning of the new Florida study. "Extreme heatwaves are becoming more frequent and intense due to climate change, and absent swift, decisive measures to reduce ocean heating and enhance coral survival, we face the danger of the disappearance of additional coral species from reefs in Florida and worldwide."

The Recent Study

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

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

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

However, researchers who performed diver surveys of more than 52,000 colonies of the species, across 391 sites along Florida's coast, found widespread, often devastating, losses.

Regional Effects

• In the Florida Keys, death rates reached 98% and even 100%, revealing a total eradication of the corals.
• In south-east Florida, where temperatures have been cooler, mortality rates were lower, at about thirty-eight percent.

Past and Current Threats

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

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

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

If temperatures remain elevated, the corals die off entirely.

Global Consequences

Globally, coral reefs are among the ecosystems most vulnerable to the human-caused climate emergency.

This presents a significant danger to:

• A quarter of all ocean life that relies upon what are effectively the marine rainforests.
• Millions of people who rely on corals to sustain fish that they can eat and earn a livelihood from.

Corals also serve as a protective barrier to safeguard our shorelines from intense hurricanes, which are themselves being worsened by rising global temperatures.

Preservation Efforts

In a desperate attempt to avert a decline of endangered corals, scientists have created repositories of Acropora in marine facilities and offshore coral nurseries.

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

But as climate change continues to escalate, there is slim chance of continued existence of these species absent significant actions, scientists caution.

Further Researcher Insight

"Elkhorn species, in particular, are some of the key wave-breaking coral species in the region," noted 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 inundation during storms, it is worthwhile taking exceptional steps to ensure we don't lose these corals altogether."