Ocean Burning Beneath The Waves, Arabian Sea Hardest Hit

While land heatwaves dominate headlines and leave people and animals gasping, a silent crisis brews beneath the waves. Across vast stretches of the Indian Ocean, sea temperatures have surged past dangerous thresholds, turning the ocean into a victim of relentless warming. These marine heatwaves now pulse through the Arabian Sea, Bay of Bengal and neighboring basins, threatening to reshape underwater ecosystems for years.

India's ocean monitoring agency has raised the alarm: the underwater spikes could bleach coral reefs, scramble fish populations, slash ocean productivity and threaten food security for millions who rely on these waters.

Indian National Centre for Ocean Information Services (INCOIS) has raised the alarm, issuing marine heatwave advisories across six major areas - from the Arabian Sea to the Andaman waters in the Bay of Bengal.

Hotspots Lighting Up Across Basins

Per an advisory dated April 20, the Arabian Sea stands out as the hardest hit. Roughly 22 per cent of the basin is under "Watch" conditions, nine per cent under "Alert," and around five per cent has escalated into "Warning" territory. The heat stretches along India's western shores - from Gujarat's arid coast southward through Maharashtra, Goa, Karnataka and Kerala - before reaching towards Oman's shores.

INCOIS uses clear thresholds based on how much sea temperatures exceed the 90th percentile of long-term daily averages:

Watch: up to 0.5 degrees Celsius above
Alert: 0.5–1 degrees Celsius above
Warning: more than 1 degree Celsius above

When waters climb into these zones for sustained periods, the effects cascade: corals expel their symbiotic algae and turn ghostly white (bleaching), pelagic fish species shift their migration routes or decline, plankton communities get disrupted, and overall marine productivity dips - potentially leading to poorer catches for fishermen.

Similar stress signals appear elsewhere. The Red Sea and Persian Gulf show impacts across about nine per cent of their waters, while the southern Indian Ocean (around islands like Madagascar, Mauritius, and Seychelles) has roughly 10 per cent affected, with four per cent in combined Alert and Warning categories. The South China Sea registers about seven per cent under heat stress.

Bay of Bengal, Southeast Asian Waters Under Pressure

In the Bay of Bengal, nearly 19–22 per cent of the area (mostly Watch, with three per cent Alert) is feeling the heat, with the strongest signals concentrated near the Andaman and Nicobar Islands and extending towards Myanmar and Thailand. These zones are biodiversity hotspots where repeated warm spells could compound existing stresses on reefs and plankton - the base of the marine food web.

Farther east, the South China Sea holds the largest share of severe "Warning" conditions (about two per cent of its area), alongside similar Alert levels. Scientists note that frequent heat events along the coasts of Vietnam, the Philippines and Malaysia are piling additional pressure on one of the planet's most species-rich marine regions, where corals are already vulnerable.

Why This Matters For People And Planet

Prolonged marine heatwaves don't stay underwater. They can disrupt tuna migration routes in the southern Indian Ocean - vital for food security across island nations and coastal nations. Along India's shores, the warming raises the odds of mass coral stress, fishery shifts and reduced ocean productivity that ripple into local economies and protein supplies for millions.

INCOIS continues to monitor these developments closely, providing updates that help fishers, policymakers and conservationists prepare. While natural variability plays a role, the broader backdrop of a warming climate makes such events more intense and frequent, turning what were once rare extremes into recurring threats.

The message from ocean scientists is clear: these warming waters are a wake-up call for the Indian Ocean's delicate balance, one that supports rich marine life and the livelihoods tied to it. Staying vigilant and reducing long-term greenhouse gas emissions will be key to giving these vital ecosystems a fighting chance.