FILE: After global sea surface temperatures reached record levels last year causing global coral bleach, biologists are working save as many species as they can. Florida Coral Rescue Center biologist Justin Zimmerman explains why coral reefs are important to Florida’s economy and how they protect the coastline.
Marine scientists tracked coral colonies in a remote area of the Great Barrier Reef and found that corals previously more resilient to bleaching suffered devastating and fatal bleaching during Australia’s 2024 summer, the fourth-ever global bleaching event.
Last year, NOAA declared the fourth-ever global coral bleaching event was underway. Worldwide bleaching is happening because of historically high sea-surface temperatures. Depending on the species of coral, ocean temperatures between 2 and 3 degrees above average is all it takes for heat stress to begin to take its toll and begin bleaching.
Previous studies found that the Great Barrier Reef experienced its hottest temperatures in 400 years during the 2024 global bleaching event.
A new study published this month by researchers at the University of Sydney studied individual colonies in One Tree Reef, located 62 miles (100 km) offshore in the Great Barrier Reef. The area has been protected from tourism and other activities for 50 years. However, the study authors found that the reef’s remote location and protected status did not save it from bleaching in 2024.
Location of One Tree Island in the southern Great Barrier Reef. (A) Map of northern Queensland with the red dot on insert showing the location of One Tree Island (OTI). (B) The locations where tracking of individual coral colonies was done, the Gutter (G) and Shark Alley (SA) are located adjacent to One Tree Island.
(University of Sydney )
“Our observations on initial responses to an intense marine heatwave show rapid bleaching, disease onset, and mortality in diverse corals, including genera that are considered resilient,” the study authors wrote. “This information is essential to predict how the species composition of coral reef ecosystems will change in a warming world.”
RECORD-BREAKING MEGA CORAL VISIBLE FROM SPACE IS POSSIBLY 300 YEARS OLD
Between February and April, 66% of the 460 colonies researchers tracked were bleaching. By July, 53% of the bleached colonies were dead and 16% recovered, according to the study.
The study also found that dying colonies can quickly turn from a “reef to rubble” under reoccurring marine heatwave conditions. The authors note that coral skeleton collapse can take months to years, depending on the location. However, by tracking individual coral colonies from bleaching to collapse, the science team found this transition can also happen quickly.
Images of individual coral colonies monitored for health assessment in February, March, and May 2024. (A) Acropora colony bleached in February, covered in algae in March and May. (B) Goniopora colony starting to pale in February, with black band disease (arrow) in March and mostly dead in May.
“These dynamics are important as heatwave mortality is becoming more frequent and reefs are increasingly becoming dominated by coral rubble,” the study authors wrote.
The University of Sydney research team warns that because of a warming planet, “we no longer have the tragedy of the distant horizon.” According to the authors, coral bleaching occurs nearly every other year on the Great Barrier Reef.