Florida’s coral reefs suffered the deadliest bleaching event in recorded history last summer, a toll caused largely by record warm coastal waters.
Now, water temperatures in the Florida Keys are already approaching the coral danger zone – earlier and hotter than last year.
It was enough for federal scientists to issue the earliest coral bleaching warning ever, an indicator that South Florida’s already struggling reef region could face another round of severe heat stress in the coming months.
“It’s a bit crazy that we’re seeing these temperatures now. Before last year, I wouldn’t even think about it until August,” said Derek Manzello, a coral reef ecologist with the National Oceanic and Atmospheric Administration. “The concern is that if temperatures are already that warm, it won’t take much for seasonal warming to push it over the edge, stressing the coral.”
Because some corals can recover from bleaching, it is too early to fully estimate last summer’s toll or accurately predict how many coral will survive successive seasons of extreme heat. But the losses are likely to be severe. Last year, an estimated half of young corals died in some underwater nurseries, where they are grown to support recovery efforts.
Scientists say the water needs to reach a ‘bleaching threshold’ of temperatures for a month before corals start to feel stressed and expel the algae that give them their dazzling colors and key nutrients. Victims of bleach turn the hard exoskeletons or corals pale white.
Last year, bleaching began in July, four to six weeks before the historic beginning. That was driven in large part by record air temperatures in South Florida during the summer, which caused the shallow coastal waters to overheat. Whether the bleaching will occur as quickly, or perhaps even sooner, will be determined by the weather in the coming weeks.
“The heat stress that Florida experienced last year was so extreme and so unexpected,” Manzello said.
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Florida is one of many places worldwide experiencing devastating coral bleaching. Since February, at least 63 other countries have experienced mass coral bleaching events.
According to NOAA, one of the biggest threats to coral reefs is climate change. Human pollution, like the burning of fossil fuels for heat and energy, is absorbed into the ocean, warming it and changing the chemistry of the water. Also, increased storms and sea level rise due to climate change can deposit sediment on the reefs and destroy them.
With water temperatures already so high, there is a danger that the largest global bleaching event in the record book will occur, Manzello said.
So far, at least some popular reefs appear resilient. The water temperature at Cheeca Rocks, a shallower reef off Isamorada that draws snorkelers, reached 86 degrees Fahrenheit, six degrees higher than average for this time of May. But despite the high water temperature, there was a positive sign:
“Everything looked good, the coral all looked healthy, there was minimal disease and virtually no bleaching,” said Allyson DeMerlis, coral researcher for NOAA and Miami Rosenstiel School of Marine, Atmospheric, and Earth Science.
Along with NOAA, other groups leading reef restoration efforts, such as the Coral Restoration Foundation, said they began planning for another difficult and challenging year as early as November.
Phanor Montoya-Maya, the Coral Restoration Foundation’s restoration program manager, said his group continues to try to breed more hearing-resistant corals in laboratory tanks — stocks that could one day be replanted on natural reefs. But the Foundation has been conducting voluntary coral planting since last June, waiting to see how conditions stabilize.
“For example, it is too early to move coral to deeper water or remove coral from the water,” Montoya-Maya said.
Another option they are considering is moving the coral further north, where last year’s bleaching was not as bad.
“Now we’re pretty much waiting to see how reality will play out,” Montoya-Maya said.
Ashley Miznazi is a climate change reporter for the Miami Herald, funded by the Lynn and Louis Wolfson II Family Foundation in partnership with Journalism Funding Partners.
