(CN) — Record temperatures in the Atlantic Ocean and the Gulf of Mexico in 2023 led to widespread coral bleaching and resulted in mass death for coral reefs across Florida, National Oceanic and Atmospheric Administration researchers said Wednesday.
The scorching highs that lasted from June to October prompted marine scientists at NOAA to step up their reef monitoring across coastal areas, they said at an hourlong public education session Wednesday.
The agency went from checking reefs yearly to monthly whenever possible, according to Nicole Besemer, an oceanographer with the federal organization. She helped present the agency's findings on coral in the Flower Garden Banks National Marine Sanctuary — the only one of its kind in the Gulf of Mexico — and in the Florida Keys.
“Our environment is becoming unsuitable for some coral — we need to monitor and find out which elements of climate affect which corals, which corals they are and what they do for our environment,” Besemer said, describing why monitoring is vital in an age of climate change.
Coral reefs represent one of the most important ecosystems in the world and are threatened by climate change.
“Coral are animals,” Besemer said. “Coral move and feed and reproduce just like animals.”
The astonishing number and diversity of wildlife in coral reefs is equaled only in a few rainforests. Coral reefs filter water so it is clean enough for wildlife to live in. They also provide essential barriers between the ocean and land, buffering shorelines from waves and storms, and offer habitat for millions of fish species.
Scientists estimate 90% of the world's coral reefs could vanish by 2050 due to extreme bleaching, which means the coral have shed the symbiotic algae that gives them color by attaching to the reef. Once the algae have moved on, the corals appear white.
Coral bleaching has many environmental causes, with extreme heat and extreme cold being the most likely predictors.
Bleached coral doesn’t necessarily mean dead coral, Besemer said. Still, 70% of Florida reefs are eroding, meaning deaths are outpacing any new growth.
But it isn’t all bad news. Scientists have identified reefs that appear to adapt quickly to rising temperatures and varying water conditions, offering hope that there are specific types of coral that are more resilient to climate and environmental changes.
Even though most corals do better in deeper, cleaner waters, there are intertidal areas just off the coast near Miami with healthy corals — “and they’re not living, they’re thriving,” Besemer said.
Scientists are examining the genes of urban coral like these to understand how reefs “might be living so well and at such extreme temperatures that change at the drop of a hat.” This is an example of coral evolution, Besemer said, and it’s encouraging.
Still, Besemer cautioned that with a wide variety of corals that have varying behaviors, any group of coral might react differently even than those in a neighboring area.
Scientists are monitoring reefs in the Florida Keys, including at the Cheeca Rocks site, a zone notable for its shallow waters.
Monitoring there showed that temperatures over most of the summer, specifically in July and August, were above the threshold where bleaching happens.
During heat waves, marine scientists expect coral bleaching to begin when water temperatures reach at least 2 degrees Fahrenheit (or 1 degree Celsius) above the typical summertime maximum.
In the Florida Keys, the bleaching threshold is 87.13 F (30.62 C). The Keys crossed that line on June 14, 2023, and remained above it until October, monitoring showed.
Following several weeks of record-breaking heat, researchers found entire segments of bleached coral.
It was “so, so devastating to see the reef” in that shape, Besemer recalled.
“I can confidently say that people who have been going to Cheeca Rocks have never seen bleaching like this,” she added.
However, reefs can come back, even from an extended period of extreme heat. In fact, some of the coral in Cheeca Rocks have.
By September the color was coming back. Besemer called the return of color “uplifting,” but noted that during the same inspection scientists also saw some corals starting to die. In October, some were full and looking healthy, while others were still bleached.
“By December, we saw a pattern where some of the tops of the corals that had been in direct sunlight were not doing well,” she said.
The Flower Garden Banks reserve far offshore from Galveston Bay in Texas, on the other hand, is far enough offshore that coral reefs survived the year's heat fairly well.
“The heat this year started a lot earlier, but we are deeper to start with and surrounded by deeper water,” she said.
The depths help keep temperatures down. On the contrary, the shallower reef in Florida bleached the earliest and most severely over the summer.
The coral in Flower Garden Banks, as with the coral in mid-channel reefs in the Keys such as Cheeca Rock, as still growing.
“That’s why we’re trying to learn the most from these reefs and why they’re doing so well,” Besemer said.
Kelly Drinnen, who oversees education and outreach at the Flower Garden sanctuary, said they are looking at which corals did the best and worst during the bleaching.
“Flower reef coral are doing well and proving to be extremely resilient because they were extremely healthy to begin with,” Drinnen said. “It’s a complex system of threats that coral reefs are facing, for instance runoff. …Things we can handle locally and individually can help keep our reefs healthy.”
NOAA began its coral reef monitoring program in 2013 to assess the health and status of coral reefs.
Besemer said that to build climate resistance, marine scientists “need to start making our impacts larger scale.”
She said researchers are putting in the hours, but the impact of their work needs to be greater to keep coral reefs healthy.
“If all those corals died in one summer, we know we need to do more,” she said.
“We just need to realize that this problem is here and it’s not in the future, and learn how to keep [coral bleaching] from getting worse.”
Researchers encourage the public to alert NOAA whenever they see bleached coral.
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