Rising CO₂ drives hypercapnic hypoxia in mangrove estuaries, endangering global fish nurseries

Key facts

• Hypercapnic hypoxia—high CO₂ and low oxygen—now occurs mildly 34–43% of the time and severely 6–32% of the time across 23 assessed mangrove sites.
• Climate change will lower oxygen by 5–35% and raise CO₂ by 8–60% in mangrove waters by 2100, making events 15 times more frequent under extreme scenarios.
• By 2100, 78% of sites will face mild hypoxia lasting 12–24 consecutive hours during heatwaves, while Amazon mangroves may experience hypercapnia 100% of the time.
• A 10°C temperature rise (20°C to 30°C) cuts dissolved oxygen by 30% and boosts CO₂ by 50%, shrinking safe nursery windows for fish.
• Commercially valuable species—common silver-biddy (Gerres oyena), silver grunt (Pomadasys argenteus), pink ear emperor (Lethrinus lentjan), and Indian goatfish (Parupeneus indicus)—are among the low-tolerance fish at risk.
• Mangroves support ~20,000 extra fish per hectare per year worth $10 million and provide livelihoods for ~4 million fishers, mainly in Brazil, Indonesia, and Tanzania.