Coral Reefs in at least 83 countries, including the coasts of East Africa, have turned white between January 2023 and April 2025, the latest data from the US government’s Coral Reef Watch shows.
At a local level, storms, disease, sediments and changes in saltiness can cause corals to bleach, but mass bleaching is largely caused by increased sea temperatures
Coral get their bright colors from the colorful algae that live inside them and are a food source for the corals. Prolonged warmth causes the algae to release toxic compounds, and the coral ejects them. A stark white skeleton is left behind, and the weakened coral is at heightened risk of dying. They can recover from bleaching if temperatures are not too extreme, but surveys done in the months after the event have begun to paint a picture of widespread coral death.
Coral reefs are known as the rainforests of the sea because of their high concentration of biodiversity that supports about a third of all marine species and a billion people.
The mass bleaching has been confirmed in the Atlantic, Pacific and Indian ocean basins, including parts the coastline of East Africa, the United States, the Caribbean, Central America, South America, Australia, the South Pacific, the Persian Gulf and Indonesia.
According to the Coral Reef Watch, the bleaching-level heat stress has impacted 84% of the world’s coral reef area. The agency deemed this ongoing bleaching event “the biggest to date,” noting that the previous record was set with 68.2% of reefs affected during the third-largest bleaching period, between 2014 and 2017. The first and second global coral bleaching events occurred in 1998 and 2010, respectively.
2024 was Earth’s hottest year on record, and much of that is going into oceans. The average annual sea surface temperature of oceans away from the poles was a record 20.87 degrees Celsius. That’s deadly to corals, which are key to seafood production, tourism and protecting coastlines from erosion and storms.
Scientists say it’s essential to reduce greenhouse gas emissions that warm the planet, such as carbon dioxide and methane.
