As of June 11, NOAA assessments indicate El Niño conditions have officially begun and are forecast to strengthen from the current time through winter in the Northern Hemisphere. This could once again elevate global coral bleaching risks in the Pacific Ocean, Caribbean and on Florida’s coral reef.
El Niño is the warm phase of the El Niño-Southern Oscillation, a naturally recurring global climate pattern characterized by above-average sea-surface temperatures in the central and eastern equatorial Pacific Ocean. The eastern equatorial winds that typically keep the warmer waters near Oceania in the western Pacific Ocean weaken and allow these warmer waters to migrate eastward to South America.
The phenomenon typically develops every two to seven years and can alter weather patterns across much of the world. Unfortunately, these warmer water temperatures can push corals beyond their thermal limits, triggering mass coral bleaching. Since 1998, every strong El Niño condition has led to a global coral bleaching event. The good news is that the El Niño weather pattern reduces predicted hurricane activity in the Atlantic Ocean; however, it is still wise to be wary, since Hurricane Andrew (1992) was during an El Niño pattern.
What is coral bleaching?
Coral bleaching occurs when corals become stressed by unusually warm water and expel the microscopic symbiotic algae called zooxanthellae living within their tissues. These microalgae provide corals with more than 90% of their food supply, and when they are absent, corals cannot feed efficiently.
In addition, without the zooxanthellae, the coral polyps lose their vibrant colors and become transparent, which causes them to appear bleached and you can see the white coral skeleton underneath. Corals can recover from bleaching, but during the event they are more vulnerable to other stressors and the lack of food can lead to mortality.
The longer the higher temperatures persist, and the higher the degrees of heating, the greater the likelihood a coral will not be able to survive a marine heat wave. NOAA Coral Reef Watch monitors conditions that can cause coral bleaching and has a global early-warning system with near-real-time sea surface temperature data. The Florida Keys National Marine Sanctuary has 17 in-water ocean monitoring sites and you cansee current underwater temperatures at aqualink.org/collections/811.
Fourth global coral bleaching event
During the summer and fall of 2023, Florida’s coral reef was part of the fourth global coral bleaching event fueled by the previous El Niño. If the Florida Keys experience another El Niño beginning this summer, that we could have another marine heat wave similar to that of 2023. Florida’s coral reef protects our beaches and coastlines by reducing effects of direct wave action and flooding. This protects infrastructure and economic activity along our coasts. Healthy coral reefs dissipate 97% of the wave energy that would otherwise erode beaches and cause property damage. Annually, coral reefs in Florida protect more than $675 million worth of property and economic activity from flooding.
From 2023 to 2025, the earlier El Niño fueled the fourth global coral bleaching event that affected coral reefs across the Atlantic, Pacific and Indian Oceans and reached an unprecedented scale. NOAA reports that coral bleaching-level heat stress affected some 84% of the world’s coral reef area between early 2023 and mid-2025, with mass bleaching documented in at least 83 countries and territories. Despite the severity of the event, scientists have identified some reefs that demonstrated surprising resilience.
Researchers are investigating why certain coral communities survived extreme heat while others suffered extensive bleaching. Understanding these natural resistance mechanisms could help guide future restoration and conservation efforts. Coral reefs are among the most biologically diverse ecosystems on Earth. They provide habitat for thousands of marine species, protect coastlines from storms and erosion, and support fisheries and tourism industries worth billions of dollars annually.
More information is available weekly from Florida’s Coral Reef Resilience Program at www.fcrrp.org.
