Climate change amplifies mangrove hypercapnic hypoxia and threatens fish habitats

Mangroves provide habitats for many marine species and support fisheries in developing tropical countries. However, mangrove habitats are increasingly threatened by climate change. Here, we show how global warming and rising atmospheric CO₂ will reduce dissolved oxygen and increase CO₂ in mangrove waters, making them less suitable as fish refugia. Global observations from 23 mangroves revealed that most sites already experience mild (on average, 34–43% of the time) or severe (6–32%) hypercapnic hypoxia, i.e., low oxygen and high CO₂ conditions. Hypercapnic hypoxia mostly occurs during low tide and in tropical mangroves. Climate projections indicate that oxygen will decrease by 5–35% and CO₂ will increase by 8–60% by 2100. Therefore, hypercapnic hypoxia events will occur more frequently, last longer, and become more severe. These shifts will reduce mangrove biodiversity and decrease habitat quality for commercially valuable fish, likely reducing fishing yields in tropical developing countries.