Discuss the role of El Niño and marine heatwaves in coral bleaching with reference to Lakshadweep and the Gulf of Mannar.

Corals bleach when heat stress makes them expel their symbiotic algae, which supply most of their nutrients [1]. The 4th Global Coral Bleaching Event (2023–25) was made worse by the 2023 El Niño and hit about 84% of the world's reef area [1][2]. El Niño raises the background ocean temperature, marine heatwaves set off the bleaching, and local conditions decide whether reefs recover.

How El Niño and marine heatwaves cause bleaching

• El Niño amplifies: it warms tropical oceans across whole basins. Every global bleaching event since 1998 has coincided with a strong El Niño [2].
• Marine heatwaves (MHWs) trigger: these are long spells of sea temperatures above the 90th percentile of normal [3].
• Heat stress adds up: INCOIS's Coral Bleaching Alert System tracks night-time sea surface temperature (SST) HotSpots and Degree Heating Weeks (DHW, heat stress accumulated over about 3 months) [4].

El Niño → basin-wide warming → Marine heatwave → DHW rises
        → algae expelled → BLEACHING → recovery (if heat ends) / mortality

Fig: From climate driver to reef damage

Lakshadweep: the worst hit

• MHWs began in late October 2023. CMFRI surveys found widespread bleaching, with DHW at levels NOAA links to a substantial bleaching risk [3].
• 84.6% bleaching in 2024, the highest in India. Government data attribute it to El Niño-linked sea warming [5].
• The islands are coral atolls, so bleaching threatens both fisheries and shoreline protection.

Gulf of Mannar: affected but more resilient

• The same warming caused only about 27% patchy bleaching, and most of it recovered [5].
• This shows that how strong and how long the local heat stress lasts decides the damage, and that reefs can recover once the heat ends.
• Local pressures such as fishing and coastal activity can still reduce this resilience.

Beyond El Niño

• NOAA warns that reefs will now bleach on a near-annual basis [2], and annual mass bleaching is projected by 2080 [1]. Climate change is turning stress that once came only in El Niño years into a constant condition.

To sum up, El Niño raises the background temperature, marine heatwaves set off bleaching, and local conditions shape recovery. India should keep its prevention-first approach of monitoring and surveillance [6]. It should link INCOIS alerts to rapid field response, reduce local stressors, and test new algae-transfer methods only as supplements [1]. Lasting protection for Lakshadweep and the Gulf of Mannar depends on cutting emissions under the Paris Agreement and meeting SDG 14 (Life Below Water).