Sea temperatures across parts of the Indian Ocean have crossed dangerous thresholds
Marine heatwaves detected across the Arabian Sea, Bay of Bengal and adjoining basins
Warming waters could trigger coral bleaching, disrupt fisheries and reduce ocean productivity
Key regions, including the Andaman waters and western Indian coastline, under heat alerts
Scientists warn prolonged heat could affect food security and livelihoods dependent on marine resources
Rising sea temperatures across the Indian Ocean have reached dangerous levels, putting fisheries, coral reefs and marine life at severe risk, India’s ocean watchdog has warned.
The Indian National Centre for Ocean Information Services (INCOIS) has issued a marine heatwave alert across six basins, from the Arabian Sea to the Andaman waters in the Bay of Bengal, highlighting widespread warming across the Indian Ocean.
As of April 20, 2026, the Arabian Sea is the most affected, followed by the Bay of Bengal.
INCOIS classifies marine heatwaves based on temperature anomalies above long-term averages. A “Watch” is issued when temperatures rise up to 0.5 degrees Celsius (°C) above the 90th percentile of daily climatology, “Alert” for 0.5-1°C, and “Warning” when temperatures exceed 1°C above this threshold.
In the Arabian Sea, about 22 per cent of the region is under Watch, 9 per cent under Alert and 1 per cent has entered the Warning category. These elevated temperatures stretch along India’s western coastline, from Gujarat towards south through Maharashtra, Goa, Karnataka, and Kerala, extending as far west as the coast of Oman.
Sea-surface temperatures crossing the 90th percentile threshold is a level associated with mass ecological disruption along India’s coastline — meaning such disruption can cause coral reef stress leading to bleaching, shifts in pelagic fisheries, reduced productivity, and altered plankton dynamics.
The Red Sea and Persian Gulf show impacts across around 9 per cent of their area, while the southern Indian Ocean records about 10 per cent. The South China Sea has around 7 per cent of its area affected.
In the Bay of Bengal, 19 per cent of the basin is under Watch conditions, with Alert levels observed over 3 per cent of the area. The most intense warming is concentrated around the Andaman and Nicobar Islands and extends eastwards towards Myanmar and Thailand.
The South China Sea has the highest share of Warning-level conditions, covering about 2 per cent of its area, with a similar proportion under Alert. Scientists warn that repeated heatwave events along coasts of Vietnam, the Philippines and Malaysia are adding to existing coral bleaching pressures in one of the world’s most biodiverse marine regions.
In the southern Indian Ocean — particularly south of Madagascar, Mauritius and Seychelles — around 4 per cent of waters are under combined Alert and Warning conditions. This raises concerns about impacts on tuna migration routes, which are critical for food security and livelihoods for millions of people.