Researchers have found that two of the most important coral species comprising Florida's reef are now ecologically extinct following a intense ocean heatwave caused catastrophic losses.
The almost complete collapse of these corals, which once formed the backbone of reefs in Florida and the Caribbean, means they can no longer play their once vital role in constructing and maintaining reef ecosystems that host a variety of marine life.
Ecological extinction is a phase preceding global extinction, a threat that now hangs for many coral species.
Researchers this month warned that a critical threshold had been reached, whereby corals around the world are set to be wiped out due to global heating, which is raising ocean temperatures to unbearable levels.
"We're running out of time," said the lead author of the recent research. "Extreme heatwaves are becoming more frequent and intense due to global warming, and without immediate, ambitious actions to slow ocean warming and boost coral resilience, we face the danger of the disappearance of even more corals from reefs in Florida and worldwide."
The new research, featured in the Science journal, examined the fate of staghorn and elkhorn coral corals off the Florida coast after 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 intricate, reef-building corals and are named because they resemble, in turn, the horns of male deer and elk.
However, scientists 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.
The two Acropora species had already suffered from decades of localized impacts in Florida, such as contaminated water from contaminants that run off the land, as well as disease.
But the 2023 heatwave has been fatal 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 algae partners living in their tissues, causing them to become ghostly white.
If temperatures stay high, the corals die off entirely.
Globally, coral reefs are among the ecosystems most vulnerable to the anthropogenic climate crisis.
This presents a significant danger to:
Corals also act as a barrier to protect our shorelines from intense hurricanes, which are themselves being worsened by increasing global heat.
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.
Efforts have been undertaken to reseed corals on reefs in Florida, too, in an effort to regain some of the 90% of coral cover disappeared off the state in the last forty years.
But as climate change continues to intensify, there is little hope of long-term survival of these species without major interventions, researchers warn.
"Elkhorn corals, especially, are some of the key wave-breaking coral species in the region," noted Andrew Baker, a ocean scientist at the University of Miami.
"They used to be common on shallow reef crests in the Caribbean, and if we want our reefs to keep safeguarding our coastlines from inundation during storms, it is worthwhile taking extraordinary measures to ensure we preserve these corals completely."
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