- Repeated marine heatwaves are hitting reefs before they can fully recover, raising the risk of long-term decline.
- Since 1998, every strong El Niño has coincided with a global coral bleaching event, and each event has affected more reef areas than the last.
- Indian reefs show sharply different responses across regions, highlighting the role of local conditions and the need for sustained monitoring of the 2026–27 El Niño.
As UN Secretary-General António Guterres says, El Niño is being “supersized” by a warming climate. The UN Environment Programme (UNEP) warns that coral reefs are being hit by new bleaching events before they have had time to recover from earlier ones.
UNEP likened reefs to “an overmatched boxer” taking repeated blows, citing findings from the Global Coral Reef Monitoring Network (GCRMN) of the International Coral Reef Initiative (ICRI).
The outlook is stark. “Multiple lines of evidence indicate that the majority (70-90%) of warm water (tropical) coral reefs that exist today will disappear even if global warming is constrained to 1.5°C,” as the Intergovernmental Panel on Climate Change warns.
The headline, however, is that marine heatwaves are narrowing the window for coral reef recovery. “Coral reefs once had decades to recover after major bleaching events. Today, they’re lucky to get five or six years,” said Manuel González Rivero, a reef expert at The Australian Institute of Marine Science and lead author of the GCRMN report. “And for many reefs affected by the unprecedented marine heatwaves in 2024, this year’s El Niño likely means they’ll have had little more than a year to begin recovering before being hit again.”
“India’s own reefs show the same trend,” said marine biologist Amruth P., assistant professor in the Department of Life Sciences at CHRIST University, Bengaluru. “A 24-year study in Lakshadweep recorded coral cover falling from about 37% to under 20% since 1998 after repeated marine heatwaves.”
The study by the Mysuru-based Nature Conservation Foundation (NCF) researchers with international collaborators found that reefs recover well only when they get about six bleaching-free years. That window is becoming increasingly rare as bleaching events arrive more frequently.
The El Niño connection
Meanwhile, the World Meteorological Organization (WMO) has noted that El Niño has become “firmly established”, marked by lasting and intensifying sea surface temperature rise across the central-eastern equatorial Pacific.
WMO-designated centres issuing global seasonal forecasts indicate a near 100% probability that El Niño will persist through September-November 2026 and December 2026-February 2027, further strengthening in the coming months and peaking towards the end of 2026.
That is bad news for coral reefs. El Niño events are closely linked to increased coral bleaching and mortality. Since 1998, every strong El Niño has been associated with a Global Coral Bleaching Event (GCBE). “There have been four GCBEs, and each event has impacted more reefs than the previous event,” Derek Manzello, Coordinator of National Oceanic and Atmospheric Administration (NOAA)’s Coral Reef Watch told Mongabay-India. NOAA is a U.S. government scientific agency.
“It is estimated that 8% of the world’s corals died during GCBE1 in 1998, with a further 14% loss from 2009-2018,” Manzello noted. During the third global event, an estimated 15% of reefs experienced more than 10% coral mortality, he added. A global assessment of GCBE4 is still underway, but global coral cover declined by 8.9% during 2023-2024.
As background ocean temperatures rise due to global warming, the additional heat associated with El Niño is more likely to push corals beyond their thermal stress thresholds. “The global mean sea surface temperature from 2019-2023 was equal to the maximum (value) recorded in 1998, which was associated with the first Global Coral Bleaching Event,” Manzello said. “Sea surface temperatures during current La Niña conditions are warmer than they were during El Niño events three to four decades ago.”
The first large-scale mass coral bleaching occurred in the eastern tropical Pacific during the then record-breaking 1982-83 El Niño. “The response of eastern Pacific reefs was a harbinger of the future of all reefs, Manzello recalled. “The 1982-83 event caused severe coral mortality in the Galapagos Islands, Panama, Columbia, and Costa Rica.” To the point that coral reefs were eliminated from the southern Galapagos Islands, as coral mortality ranged from 95- 99%, as research by Manzello and colleagues found.
“The coral reefs of the Eastern Tropical Pacific represent a marginal reef system that exists at the edge of the environmental tolerance limits of corals,” Manzello explained. “These are low diversity reefs, with a small number of species relative to reefs in the Indo-Pacific. A primary reason for this is that this region is effectively ground zero for the El Niño-Southern Oscillation (ENSO) and experiences the most extreme environmental changes during ENSO events.”
“Encouragingly, the reefs in Pacific Panama exhibited increased resilience after the 1982-83 El Niño, but these same reefs are severely bleached right now, and their fate following the current El Niño is uncertain,” Manzello added.
Stories from closer to home
El Niño events have been linked to widespread coral bleaching and mortality across the Indian Ocean. The region experienced some of the most severe impacts of the first Global Coral Bleaching Event in 1998.
More recently, reefs across five regions of India, covering much of the subcontinent’s coral reef habitats, suffered significant damage. Between 2023 and 2025, more than 80% of tropical coral reefs experienced extreme heat stress coinciding with the 2023 El Niño and the fourth global mass coral bleaching event, according to a nationwide collaborative study led by NCF’s Wenzel Pinto.
Lakshadweep emerged as the worst-hit region in India in the study, with up to 37% of coral cover bleached or dead, compared with just 11.5% in the Mahatma Gandhi Marine National Park in the Andaman Islands. Some coral groups were particularly vulnerable, but the impacts varied sharply across regions. In Palk Bay, for instance, only 13.6% of the usually vulnerable reef-building Acropora corals were bleached or dead, while mortality reached 61.8% among the boulder-like Porites, generally considered more heat-resistant. The findings suggest that local ocean conditions can significantly influence how reefs respond to rising temperatures, sometimes overturning established patterns of coral vulnerability.
These diverse responses and recovery timelines may offer a glimpse of the future for reefs worldwide, as the study suggests — some coral reefs may collapse, while others persist or adapt, depending heavily on local conditions. Tracking which reefs recover — and how quickly — will be crucial as marine heatwaves intensify.
Pinto told Mongabay-India that the decline reflected slower recovery after each bleaching event, even as coral mortality — both absolute and proportional — fell with successive events. The study found that recovery rates rose sharply after six bleaching-free years, suggesting this may be a critical window for reefs to rebound.
The task before the conservation scientists and coral reef experts now is to closely watch the current El Niño phase and its impacts, Amruth noted. Recently, 188 ecologists and conservationists across India have signed a Call to Action seeking stronger research and long-term monitoring of the ecological impacts of the 2026-27 El Niño.
Banner image: A fish swims through bleached coral reefs in Caribbean waters near Panama in August this year. Representative image. (AP Photo/Matias Delacroix, File)
