Record-high Water Temperatures Cause Early Bleaching of Florida Keys Coral Reefs, Warn Scientists

This summer, several coral reefs in the Florida Keys are experiencing discoloration earlier than expected due to unprecedented water temperatures, indicating potential health hazards and stress, according to federal scientists.

Katey Lesneski, Research and Monitoring Coordinator for Mission: Iconic Reefs—a program by the National Oceanic and Atmospheric Administration (NOAA) aimed at preserving Florida’s coral reefs—states that the corals, which should be in full color this season, are rapidly turning white.

“Signs of bleaching are already noticeable as corals appear to be losing their color and turning stark white. And we still have more to witness,” Lesneski, who has spent considerable time on the reefs in the past fortnight, revealed.

NOAA scientists have recently escalated their coral bleaching warning to Alert Level 2—the highest heat stress level— which is reached when the average water surface temperature exceeds the usual maximum by approximately 1.8 degrees Fahrenheit (1 degree Celsius) for a continuous eight-week period.

Jacqueline De La Cour, Operations Manager for NOAA’s Coral Reef Watch program, stated that the surface temperatures around the Keys have averaged about 91 degrees (33 Celsius), significantly higher than the typical mid-July average of 85 degrees (29.5 Celsius). Prior Alert Level 2s were observed in August, she added.

Corals, formed by numerous tiny organisms that connect together, derive their color from the algae they house and depend on for nourishment. Excessive temperatures cause the coral to expel this algae, rendering the reefs white or bleached. While this does not equate to the death of the coral, it leaves them vulnerable to starvation and disease.

Initial signs of bleaching were detected on some coral reefs as early as two weeks ago, reports Andrew Bruckner, Research Coordinator at the Florida Keys National Marine Sanctuary. In recent days, some reefs have entirely lost their color—a phenomenon previously unrecorded before August 1st. Traditionally, bleaching peaks around late August or September.

“The process is running at least one to two months ahead of schedule,” Bruckner noted. “While we haven’t witnessed any mortality from bleaching yet and only a minor number of corals have turned completely white, the early signs are concerning.”

Forecasting the remainder of the summer remains challenging, De La Cour and Bruckner expressed. Although a further increase in water temperatures could be disastrous, potential tropical storms or hurricanes could stir up the water and cool it down. Additionally, the arrival of dusty air from the Sahara Desert over Florida could temper the sun’s rays and reduce temperatures.

Climate change and other factors have resulted in an 80% to 90% loss of coral in the Keys waters over the past half-century, according to Bruckner. This not only impacts marine life relying on the reefs but also human populations. Coral reefs serve as a natural barrier against storm surges, and tourism-based activities such as fishing, diving, and snorkeling depend heavily on these reefs.

Efforts to restore Florida’s coral to about 90% of its state 50 years ago have begun as part of a large-scale, 20-year project. The scientists are exploring breeding heat-resistant corals and implementing measures like shade covers and underwater fans to keep the waters cool and promote their survival.

Jason Spadaro, Coral Reef Restoration Program Manager for Mote Marine Laboratory & Aquarium, emphasized the importance of breeding corals for developing heat resistance in future generations.

It’s noted that the extent of coral bleaching is more severe in the lower Keys compared to the northern parts. The Keys have had bad bleaching years before, but this year, the situation is “extremely severe and persistent,” Spadaro stated.

Ross Cunning, a Research Biologist at Shedd Aquarium in Chicago, echoes the concern, pointing out that the unusually high water temperatures could lead to a catastrophic bleaching event.

De La Cour emphasizes the critical role of addressing human-induced global warming for the survival of corals.

“If we fail to decrease our greenhouse gas emissions and don’t address the gases already in our atmosphere, we are paving the way towards a world where coral reefs cannot thrive, regardless of our efforts,” she concluded.

Reporting by Whittle from Portland, Maine.

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Frequently Asked Questions (FAQs) about Coral Bleaching

More about Coral Bleaching

• National Oceanic and Atmospheric Administration (NOAA)
• NOAA’s Coral Reef Watch program
• Florida Keys National Marine Sanctuary
• Mote Marine Laboratory & Aquarium
• Shedd Aquarium
• Mission: Iconic Reefs
• Climate Change Impact on Coral Reefs