Scientists have discovered that two of the most important coral species comprising Florida's reef have become functionally extinct after a withering ocean heatwave led to devastating losses.
The near-total decline of these corals, which once served as the backbone of reefs in Florida and the Caribbean, means they are no longer able to play their previously crucial role in constructing and maintaining reef ecosystems that support a variety of marine life.
Functional extinction is a phase before total extinction, a threat that now hangs for many coral species.
Scientists recently alerted that a tipping point had been reached, whereby corals globally are set to be eradicated due to climate change, which is raising ocean temperatures to intolerable levels.
"We're running out of time," said Ross Cunning of the recent research. "Severe marine heatwaves are becoming more frequent and intense due to climate change, and without swift, decisive measures to reduce ocean heating and enhance coral survival, we face the danger of the extinction of even more corals from reefs in Florida and around the world."
The new research, published in the Science journal, analyzed the outcome of staghorn coral and elkhorn corals off the Florida coast following a intense marine heatwave in 2023.
This event raised temperatures on Florida's deteriorating coral reefs to their highest levels in more than a century and a half.
The two species are complex, reef-forming corals and are named because they resemble, respectively, the antlers of stags and elk.
However, researchers who performed diver surveys of over fifty-two thousand colonies of the species, across nearly four hundred sites along Florida's coast, found widespread, often devastating, losses.
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 illness.
But the 2023 heatwave has proved lethal for these heat-sensitive species.
The 2023 event caused the ninth occurrence 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 remain elevated, the corals die off completely.
Globally, coral reefs are among the ecosystems most vulnerable to the anthropogenic climate emergency.
This poses a major threat to:
Corals also serve as a protective barrier to safeguard our shorelines from powerful storms, which are themselves being intensified by increasing global heat.
In a desperate attempt to avert a death spiral of threatened corals, scientists have created repositories of Acropora in aquariums and offshore coral nurseries.
Efforts have been undertaken to replant corals on reefs in Florida, too, in an effort to regain some of the ninety percent of coral cover disappeared off the state in the past four decades.
But as climate change continues to escalate, there is slim chance of long-term survival of these species absent major interventions, scientists caution.
"Elkhorn species, especially, are some of the key wave-breaking coral species in the area," noted a study co-author, a ocean scientist at the University of Miami.
"They were once abundant 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 preserve these corals altogether."
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