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Environment & Ecology April 23, 2026 4 min read Daily brief · #13 of 38

INCOIS flags rising marine heatwaves in Arabian Sea, warns of ecological impact

The Indian National Centre for Ocean Information Services (INCOIS) has flagged a significant and rising trend of marine heatwaves (MHWs) in the Arabian Sea, ...

GS Paper I (Physical Geography); GS Paper III (Environment & Ecology; Disaster Management)

What Happened

  • The Indian National Centre for Ocean Information Services (INCOIS) has flagged a significant and rising trend of marine heatwaves (MHWs) in the Arabian Sea, with sea surface temperatures breaching the 90th percentile threshold and triggering Watch, Alert, and Warning advisories under its Marine Heatwave Advisory Service (MAHAS).
  • The frequency and duration of marine heatwave days in the northern and southeastern Arabian Sea are increasing at approximately 20 additional days per decade (1.5–2 additional events per decade), consistent with accelerating global ocean warming.
  • INCOIS has warned of severe ecological consequences including coral bleaching, disruption of fish migration patterns, reduced fish availability, and degradation of marine food chains in India's most economically productive fishing zone.
  • The Arabian Sea accounts for approximately 67% of India's marine fish catch from its Exclusive Economic Zone (EEZ), making the heatwave threat directly relevant to livelihoods of millions of coastal and fishing community members.
  • Warming waters are also linked to intensifying cyclone activity in the Arabian Sea, with warmer sea surface temperatures providing greater energy for storm development — a monsoon-season concern.

Static Topic Bridges

Marine Heatwaves — Definition, Causes, and Measurement

A marine heatwave is defined as a period of five or more consecutive days during which sea surface temperature (SST) exceeds the 90th percentile of the climatological baseline (typically a 30-year mean). MHWs are classified into categories — Watch, Advisory, Alert, and Warning — based on the magnitude of thermal anomaly. They are distinct from gradual ocean warming: MHWs are discrete extreme events superimposed on the long-term warming trend.

  • Causes include suppressed wind mixing (allowing surface heat retention), high-pressure atmospheric systems reducing evaporative cooling, positive feedback from reduced cloud cover, and underlying long-term ocean warming driven by anthropogenic climate change.
  • The Arabian Sea has experienced a documented increase in MHW frequency and intensity since the 1980s, compounded by weakening of the Indian Ocean Dipole and changes in monsoon circulation.
  • MHWs affect the full marine ecosystem cascade: from phytoplankton (disrupted by thermal stratification reducing nutrient upwelling) to apex predators dependent on fish stocks.
  • Globally, between 2016–2021, an estimated 50% of ocean surface area experienced at least one MHW annually.

Connection to this news: INCOIS's MAHAS advisory system is India's institutional response to this emerging hazard; the current warning signals that the Arabian Sea has crossed critical thermal thresholds that trigger ecological chain reactions.

INCOIS — Mandate, Functions, and Ocean Services

INCOIS is an autonomous institution under the Ministry of Earth Sciences, established in 1999 and headquartered in Hyderabad, Telangana. Its core mandate is to provide ocean information and advisory services to society, industry, government, and the scientific community through sustained ocean observation and research.

  • Key services: Ocean State Forecast (OSF), Potential Fishing Zone (PFZ) advisories, Indian Tsunami Early Warning Centre (ITEWC), storm surge predictions, and the Marine Heatwave Advisory Service (MAHAS).
  • INCOIS's ITEWC was designated a Regional Tsunami Service Provider by UNESCO's Intergovernmental Oceanographic Commission (IOC) in 2012, covering the Indian Ocean region.
  • INCOIS serves as the National Oceanographic Data Centre and the Regional Argo Data Centre for the Indian Ocean.
  • PFZ advisories issued by INCOIS directly benefit around 4 million fishers by indicating areas of high fish concentration, reducing fuel consumption and fishing time.

Connection to this news: INCOIS's MAHAS system enables real-time detection and tiered alerting of marine heatwave conditions — the current Arabian Sea warning demonstrates this operational capability and underscores the institution's growing role in climate-linked ocean risk management.

Ecological Impact of Marine Heatwaves on Indian Fisheries and Coral Systems

India has a coastline of approximately 7,516 km and an EEZ of 2.02 million km². The Arabian Sea, particularly the Eastern Arabian Sea (off India's west coast — Kerala, Karnataka, Goa, Maharashtra, Gujarat), is India's most productive fishing ground. The Lakshadweep Islands host coral reef ecosystems especially vulnerable to thermal bleaching.

  • Coral bleaching occurs when SST rises just 1–2°C above the mean summer maximum for 4+ weeks, causing corals to expel their symbiotic algae (zooxanthellae) and turn white; if heat stress persists, corals die.
  • Thermal stratification during MHWs suppresses upwelling of cold, nutrient-rich water, reducing the phytoplankton productivity that anchors the entire marine food web.
  • India's total marine fish production was approximately 4.1 million tonnes in 2022–23, with the western coast contributing the majority; disruption of Arabian Sea ecology directly threatens this output.
  • Lakshadweep's coral reefs, already stressed by back-to-back bleaching events in 2016, 2020, and 2024, face reduced recovery time as MHW frequency increases.
  • Marine heatwaves also affect sea turtle nesting and cetacean (whale and dolphin) migration routes, with broader biodiversity implications.

Connection to this news: INCOIS's warning is particularly significant given the timing — rising temperatures ahead of the southwest monsoon season (June–September) can disrupt pre-monsoon fishery productivity, affect cyclogenesis, and exacerbate coastal community vulnerability.

Key Facts & Data

  • INCOIS established: 1999; headquartered in Hyderabad, Telangana
  • INCOIS under: Ministry of Earth Sciences, Government of India
  • Marine heatwave threshold: SST exceeding 90th percentile for ≥5 consecutive days
  • Arabian Sea MHW trend: ~20 additional heatwave days per decade
  • Arabian Sea share of India's EEZ fish catch: ~67%
  • India's coastline length: ~7,516 km; EEZ: ~2.02 million km²
  • INCOIS ITEWC designated by UNESCO-IOC: 2012
  • India's marine fish production (2022–23): ~4.1 million tonnes
  • Coral bleaching trigger: SST 1–2°C above mean summer maximum for ≥4 weeks
On this page
  1. What Happened
  2. Static Topic Bridges
  3. Marine Heatwaves — Definition, Causes, and Measurement
  4. INCOIS — Mandate, Functions, and Ocean Services
  5. Ecological Impact of Marine Heatwaves on Indian Fisheries and Coral Systems
  6. Key Facts & Data
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