Mangroves, Their Significance & Rising CO₂ Threats
24 Mar 2026
Mangroves, Their Significance & Rising CO₂ Threats
Context: A new global study (AGU, 2026) shows that mangrove-lined estuaries are increasingly experiencing hypercapnic hypoxia (high CO₂ + low oxygen), driven by climate change. This threatens biodiversity, fisheries, and livelihoods in tropical developing countries.
What are mangroves?
- Mangroves are salt-tolerant trees and shrubs found along tropical and subtropical coastlines.
- They thrive in estuaries, tidal creeks, and coastal wetlands, where freshwater meets seawater.
- Globally, mangroves cover about 15 million hectares, acting as a crucial buffer between land and sea.
- India: Found along east & west coasts, majorly in Sundarbans (West Bengal), Bhitarkanika (Odisha), Pichavaram (Tamil Nadu), and Andaman & Nicobar Islands.
Why are they significant?
- Biodiversity Hotspots: Provide nursery grounds (for 90% of aquatic species along India’s east coast) for fish, crabs, shrimp, and other marine species.
- Livelihoods: Support ~4 million fishers worldwide, especially in developing countries.
- Coastal Protection: Reduce erosion, storm surges, and flooding by stabilising shorelines.
- Carbon Storage: Among the most effective natural carbon sinks, storing up to five times more carbon per hectare than tropical forests.
- Economic Value: Mangroves support ~20,000 additional fish per hectare annually, worth ~$10 million in ecological services.
How can rising CO2 levels affecting mangroves ecosystem?
Hypercapnic Hypoxia: Climate change is driving high CO₂ and low oxygen states in mangrove waters.
- Already observed in 34–43% mild and 6–32% severe conditions across global sites.
- By 2100, oxygen may decline by 5–35%, while CO₂ could rise by 8–60%.
Impact on Fish & Biodiversity:
- Shrinks the safe window for fish to use mangrove nurseries.
- Shifts species composition away from reef-associated fish like silver-biddy, silver grunt, pink ear emperor, and Indian goatfish, which are vital for fisheries.
Temperature Stress: A 10°C rise in water temperature can reduce oxygen by 30% and increase CO₂ by 50%, worsening hypoxia.
Livelihood Risks: Millions of coastal communities (in Brazil, Indonesia, Tanzania, India, and other tropical nations), depending on mangrove fisheries face declining catches and income.
Long-Term Hazard: Sediments and tidal channels may trap CO₂-rich waters, making conditions even more extreme inside mangrove forests.
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