A network of coral reef scientists have announced that the world is currently experiencing its fourth global coral bleaching event, the second to hit reefs in the past ten years.

The announcement, made by the National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI), yesterday, comes at a time when coral reefs are facing a number of threats to their survival.

Bleaching-level heat stress, caused by prolonged increases in ocean temperatures has become extensive across the Pacific, Atlantic, and Indian Oceans.

“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 the Coordinator of NOAA’s coral reef watch program, Dr. Derek Manzello.

Mass bleaching of coral reefs has been confirmed in at least 53 countries, territories, and local economies, including large areas of the South Pacific (Fiji, Vanuatu, Tuvalu, Kiribati, and the Samoas), Australia’s Great Barrier Reef, Florida, the Caribbean, the Eastern Tropical Pacific (including Mexico, El Salvador, Costa Rica, Panama, and Colombia), the Red Sea (including the Gulf of Aqaba), the Persian Gulf, and the Gulf of Aden.

Reports have now been confirmed of widespread bleaching across parts of the Western Indian Ocean, including Tanzania, Kenya, Mauritius, the Seychelles, Tromelin, Mayotte, and off the western coast of Indonesia.

Coral bleaching becoming more severe

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Manzello said. “When these events are sufficiently severe or prolonged, they can cause coral mortality, which can negatively impact the goods and services coral reefs provide that people depend on for their livelihoods.”

When coral bleaching kills the reefs on a widespread scale it imacts economies, livelihoods, food security. However, coral bleaching does not always lead to coral death. If the stress driving the bleaching diminishes, corals can recover.

“Climate model predictions for coral reefs have been suggesting, for years, that bleaching impacts would increase in frequency and magnitude as the oceans warm,” said the Director of NOAA’s coral reef conservation program, Jennifer Koss.

Global action needed

The International Coral Reef Initiative (ICRI), a partnership of 101 international members, currently co-chaired by NOAA and the U.S. Department of State, is applying resilience-based management actions for coral reefs.

CEO of the Khaled bin Sultan Living Oceans Foundation, Alexandra Dempsey said that one of the best ways to assess the impact of a bleaching event is to track changes to a reef over time. “Reliable baseline data on the state of the reef such as the data on coral cover, fish biomass, and species diversity we collected on the Foundation’s Global Reef Expedition can help scientists assess the impact of the bleaching event and understand how the health of a reef changes over time.”

Regular coral reef monitoring

However, global bleaching events does not affect all coral reefs equally and require a suite of global, regional, and local interventions. This emphasises the importance of regularly monitoring coral reef ecosystems, and not just during bleaching events.

Networks such as the Global Coral Reef Monitoring Network, an operational network of ICRI, and the U.S. Coral Reef Task Force, provide mechanisms for reporting on the impact of bleaching on the World’s coral reefs, alongside regional bleaching observation networks.

“As the Living Oceans Foundation continues to work on coral reefs, particularly in the South Pacific, we have been called upon by NOAA to report on active bleaching events we have witnessed in the field,” said Dempsey. “This is critical for real-time reporting for the global status of coral reef bleaching events.”

The ICRI will be hosting a webinar on 14 May to discuss the status of the 4th Global Bleaching Event and the role of the global coral reef community.

The Khaled bin Sultan Living Oceans Foundation is a US-based nonprofit environmental organisation that protects and restores the world’s oceans through scientific research, outreach, and education.