Record ocean temperatures across the world are continuing to take a toll on coral reefs.

Scientists at National Oceanic and Atmospheric Administration (NOAA) said on 15 April that the world is currently experiencing a global coral bleaching event. This is the fourth global event on record and the second in the last 10 years.

According to the agency, bleaching occurs when corals are stressed by changes in conditions such as temperature, light, or nutrients. They expel the symbiotic algae living in their tissues, causing them to turn completely white.

An explainer on the NOAA website further adds: “Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.”

In the 15 April news release, the agency said bleaching-level heat stress, which is remotely monitored and predicted by NOAA’s Coral Reef Watch (CRW), has been — and continues to be — extensive across the Atlantic, Pacific and Indian Ocean basins. This heat-stress monitoring is based on sea surface temperature data, spanning 1985 to the present, from a combination of NOAA and partner satellites.

“From February 2023 to April 2024, significant coral bleaching has been documented in both the Northern and Southern Hemispheres of each major ocean basin,” said Derek Manzello, Ph.D., NOAA CRW coordinator.

Since early 2023, mass bleaching of coral reefs has been confirmed throughout the tropics, including in Florida in the US; the Caribbean; Brazil; the eastern Tropical Pacific (including Mexico, El Salvador, Costa Rica, Panama and Colombia); Australia’s Great Barrier Reef; large areas of the South Pacific (including Fiji, Vanuatu, Tuvalu, Kiribati, the Samoas and French Polynesia); the Red Sea (including the Gulf of Aqaba); the Persian Gulf; and the Gulf of Aden, the news release said.

The agency has also received confirmation of widespread bleaching across other parts of the Indian Ocean basin as well, including in Tanzania, Kenya, Mauritius, the Seychelles, Tromelin, Mayotte and off the western coast of Indonesia.

Coral bleaching also has a direct impact on livelihoods, food security, economies and more. “Climate model predictions for coral reefs have been suggesting for years that bleaching impacts would increase in frequency and magnitude as the ocean warms,” said Jennifer Koss, director of NOAA’s Coral Reef Conservation Program.

Also read: Restored coral reefs show incredible speed of recovery: Study