Rescuing Corals Amid Mass Bleaching and Record-High Oceans Temperatures in 2023

Wednesday - August 23 2023, 05:13 UTC - 1 year ago

A marine heat wave in late July 2023 has triggered widespread coral bleaching off Florida and beyond, putting the foundation species of shallow tropical waters at risk. Scientists and volunteers are in a race against time, collecting thousands of corals and transplanting them to cooler waters in an effort to save them before the long periods of high heat kills them.

Armed with scrub brushes, young scuba divers took to the waters of Florida’s Alligator Reef in late July to try to help corals struggling to survive 2023’s extraordinary marine heat wave. They carefully scraped away harmful algae and predators impinging on staghorn fragments, under the supervision and training of interns from Islamorada Conservation and Restoration Education, or I.CARE.

Normally, I.CARE’s volunteer divers would be transplanting corals to waters off the Florida Keys this time of year, as part of a national effort to restore the Florida Reef. But this year, everything is going in reverse.

As water temperatures spiked in the Florida Keys, scientists from universities, coral reef restoration groups and government agencies launched a heroic effort to save the corals. Divers have been in the water every day, collecting thousands of corals from ocean nurseries along the Florida Keys reef tract and moving them to cooler water and into giant tanks on land.

Marine scientist Ken Nedimyer and his team at Reef Renewal USA moved an entire coral tree nursery from shallow waters off Tavernier to an area 60 feet deep and 2 degrees Fahrenheit (1.1 Celsius) cooler. Even there, temperatures were running about 85 to 86 F (30 C).

Their efforts are part of an emergency response on a scale never before seen in Florida.

The Florida Reef – a nearly 350-mile arc along the Florida Keys that is crucial to fish habitat, coastal storm protection and the local economy – began experiencing record-hot ocean temperatures in June 2023, weeks earlier than expected. The continuing heat has triggered widespread coral bleaching off Florida in particular, but also beyond.

By mid-August, coral bleaching had been reported in the Bahamas, Cuba, Mexico, Belize, El Salvador, Costa Rica, Panama and Colombia, as well as Puerto Rico and the U.S. Virgin Islands. This is particularly devastating because some of the healthiest remaining coral reefs are in the southern Caribbean. Scientists worry they may be seeing the sixth mass bleaching of Caribbean corals since 1995 and the third within the past 12 years, and the heat is likely to continue.

While corals can recover from mass bleaching events, long periods of high heat can leave them weak and vulnerable to disease that can ultimately kill them.

That’s what scientists and volunteers have been scrambling to avoid.

The Florida Reef has struggled for years under the pressure of overfishing, disease, storms and global warming that have decimated its live corals.

A massive coral restoration effort – the National Oceanic and Atmospheric Administration’s Mission: Iconic Reef – has been underway since 2019 to restore the reef with transplanted corals, particularly those most resilient to the rising temperatures. But even the hardiest coral transplants are now at risk.

Reef-building corals are the foundation species of shallow tropical waters due to their unique symbiotic relationship with microscopic algae in their tissues.

During the day, these algae photosynthesize, producing both food and oxygen for the coral animal. At night, coral polyps feed on plankton, providing them with essential nutrients that help them grow.

But this year, warmer waters and the fear of an even hotter summer has caused conservationists to hit the pause button and instead of transplanting corals into the sea, they are trying to do the opposite and rescue the corals from the sea to save them from the impending heat.