Coral Comeback: Last Summer's Bleaching Crisis Cools Off

When Chris Langdon went diving in late August, he witnessed a unique sight: the severe bleaching event that occurred after the 2023 summer heat warmed Florida’s waters.

As Langdon explored the area, located at the Southern end of Biscayne Bay and near the northern tip of Key Largo, some of the corals he saw were bleached, dead, or in the early stages of bleaching. The site had started recovering from the previous bleaching event in 2014, and some species were beginning to come back strong. However, the once-colorful corals changed during the summer of 2023. 

The freshly bleached corals were bone white, while some others in the next stage had turned a fuzzy brown as algae began to grow on them. Some corals in the early stages of bleaching were getting pale and greenish-yellow.

“Those were sort of on their way out,” said Langdon, a marine biology and ecology professor at the University of Miami, “but depending on when the water cooled, there was still a chance for those corals to recover.”

Some scientists call it the worst bleaching event Florida has experienced. As water temperatures cool down, some coral experts feel optimistic about their recovery, while others remain uncertain.

Coral bleaching refers to an event in which stress causes corals to expel the symbiotic algae, called zooxanthellae, that live in their tissues. As a result, the corals turn white. Some possible stressors are changes in temperature, light or nutrients. According to the National Oceanic and Atmospheric Administration (NOAA), “Corals can survive a bleaching event, but they are under more stress and are subject to mortality.”

According to Langdon, the major effort coral reef scientists are doing to help the reefs is growing corals in nurseries and attaching them to the reefs to replace corals that have died from  bleaching. However, this does have its limits.

“There’s millions of corals out there, so it’s kind of a band-aid  on a very, very big problem,” he said.

However, Langdon explained some corals have adaptations that allow them to deal with the heat, and he believes coral restoration efforts would be better served if researchers and scientists first used the more heat-tolerant genotypes of corals in these efforts.

Climate change is causing unprecedented sea surface temperatures, and along with increased acidification, this has caused adverse effects on corals, according to Mark Bush, a professor of ocean engineering and marine sciences at the Florida Institute of Technology.

Bush explained that corals begin to bleach when ocean surfaces heat up to above 30 degrees Celsius. As a result, the reef loses its structure, and many of the reef’s critters follow.

“There’s no good outcome from it,” Bush said. He said the future of Florida’s corals looks bleak, aside from some deep-water corals that may survive, unless humans change the carbon release that drives global warming.

Bush added that when storms batter a reef, if the corals are bleaching, these corals’ capacity to repair the reef is reduced or gone. Over the course of a few decades of this happening, fringing reefs, the reefs that grow along the shoreline, are lost. The loss of the reefs causes more wave action to affect the exposed shorelines.

According to The Reef Institute’s Executive Director, Leneita Fix, corals have suffered from stony coral tissue loss disease, which is highly lethal. After the 2023 summer bleaching event, Florida’s coral reefs are now in a precarious position.

However, Fix explained people pose the biggest threat to corals and that people need to help individually through methods such as using reusable water bottles. She added that people must help as a community.

Fix said more people from all areas need to become involved in restoration so that coral experts can have the workforce they need to help the coral reefs.

Coral reefs provide many benefits, including jobs and opportunities for recreation. They also protect coastlines from storms and erosion, and they even serve as a food and medicine source. 

Additionally, according to the Florida Keys National Marine Sanctuary, “NOAA suggests that coral reefs in southeast Florida have an asset value of $8.5 billion, generating $4.4 billion in local sales, $2 billion in local income, and 70,400 full and part-time jobs.”

Despite the many threats corals have faced, Fix remains optimistic.

“As bad as things are, there is still hope,” she said.

Fix explained that corals can adapt well if they are given the chance. She said there is a type of algae that is more resilient than others, and it makes the corals very resilient. She said it is important for people to conserve what is left of the reefs, but they also need to look to restoration and remain hopeful.

“When you become hopeless, then you do nothing,” she said.

Mark Bush believes recovery may be possible if the planet cools, but this recovery could also be a challenge.

“That means banning fossil fuels and changing our lifestyles, and people aren’t willing to do that,” he said.