‘Should be a global wake-up call’: Coral reefs suffer fourth mass bleaching event

The world’s coral reefs are undergoing a severe crisis, marked by the fourth global bleaching event on record—the second such event within the last decade. According to the National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI), extensive coral bleaching has been documented globally from February 2023 to April 2024. This phenomenon signals a dire warning about the escalating impacts of climate change on these vital underwater ecosystems.

The current global bleaching has touched virtually every corner of the world’s tropical oceans. Areas from Florida’s coastlines to the vast expanse of Australia’s Great Barrier Reef and from the densely populated regions of the Caribbean to remote waters of the South Pacific including Fiji, Vanuatu, and French Polynesia, are witnessing similar fates. Coral ecosystems in the Red Sea, the Persian Gulf, and the Gulf of Aden have not been spared. Reports confirm widespread bleaching even further, in places like Tanzania, Kenya, Mauritius, and off the western coast of Indonesia.

NOAA’s Coral Reef Watch (CRW), utilizing sophisticated sea-surface temperature data collected from a blend of NOAA and partner satellites, has been pivotal in predicting and monitoring these events. According to Derek Manzello, Ph.D., coordinator of NOAA CRW, the data collected since 1985 paints a grim picture of increasing ocean temperatures and consequent coral stress levels. “As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Manzello reported. This year’s event has been so extensive that over half the planet’s reefs have experienced bleaching-level heat stress.

Coral reefs, often referred to as the “rainforests of the sea,” are home to thousands of marine species. The loss of coral health through bleaching—where corals expel the algae living in their tissues due to stress, leading to a whitened state—can be catastrophic. Although not immediately fatal, bleached corals are under significant distress, with diminished ability to grow and reproduce. This jeopardizes the entire marine food chain, from small fish that rely on corals for shelter to apex predators whose prey populations are intertwined with reef health.

The ramifications of coral bleaching extend beyond environmental loss. Economies that rely on coral reefs for tourism, fishing, and shoreline protection against storms face dire consequences. Communities living near bleached reefs can experience significant downturns in tourism revenue, reduced fish catches, and increased vulnerability to coastal erosion and storms.

The linkage between coral bleaching and global warming is irrefutable. Rising ocean temperatures, a direct consequence of increased greenhouse gas emissions from fossil fuel combustion, have set new records. Research underscores that the ongoing rise in global ocean surface temperatures could be setting the stage for more frequent and severe bleaching events. “Temperatures are off the charts,” stated Emily Darling, director of coral reefs at the Wildlife Conservation Society.

In response to the escalating coral crisis, NOAA’s Coral Reef Conservation Program has ramped up efforts on resilience-based management practices. Since the publication of the 2019 Interventions to Increase the Resilience of Coral Reefs study by the National Academies of Sciences, strategic efforts have included moving coral nurseries to deeper, cooler waters and deploying sunshades to protect corals. These actions are part of a broader strategy to mitigate the impacts of marine heatwaves and local stressors, which was significantly tested during the unprecedented 2023 heatwave in Florida.

The International Coral Reef Initiative, co-chaired by NOAA, plays a critical role in fostering global cooperation towards coral conservation. Through sharing resilience-based management actions and lessons learned, ICRI and its international members aim to advance coral interventions and restoration in the face of climate change.

“The announcement of the fourth global bleaching event is an urgent call to do two things: reduce greenhouse gas emissions and work together to prioritize resilient coral reefs for conservation,” said Darling.


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