Smithsonian-led analysis, the first of its kind, also shows that an even more severe event is unfolding now

Peer-Reviewed Publication
Smithsonian

Benefits to society from coral reefs, including fisheries, tourism, coastal protection, pharmaceutical discovery and more, are estimated at about $9.8 trillion per year. For the first time, an international team led by Smithsonian researchers estimated the extent of coral bleaching worldwide during a global marine heatwave, finding that half of the world’s reefs experienced significant damage. Another heatwave began in 2023 and is ongoing. The analysis was published today in Nature Communications.

It takes two partners to make a coral: a tiny animal related to a jellyfish that secretes the hard coral structure and an even tinier algae that turn sunlight into the energy the animal partner needs to live. Bleaching occurs under heat stress, when the partnership breaks down, and the coral loses its algal symbionts—its source of energy—and turns white. Bleaching leads to reduced growth, less reproduction and even death when it is especially severe or sustained.

To obtain their estimate of the extent of reef damage from the “Third Global Coral Bleaching Event” (2014–2017), an international team from dozens of countries worldwide, led by researchers at the Smithsonian Tropical Research Institute (STRI), James Cook University in Australia and the former director of Coral Reef Watch at the U.S. National Oceanic and Atmospheric Administration (NOAA), combined satellite images of ocean water temperature from the Coral Reef Watch system with reef observations from in the water and aerial surveys around the world.

“This is the most geographically extensive analysis of coral bleaching surveys ever done,” said Sean Connolly, a senior scientist at the Smithsonian. “Nearly 200 co-authors from 143 institutions in 41 countries and territories contributed data.”

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