akar.earthBlue carbon: Definition
What is blue carbon? Carbon stored in mangroves, seagrass and tidal marshes, how it is measured for credits, and why Indonesia is a global blue carbon leader.
Blue carbon is the carbon captured and stored by coastal and marine ecosystems, mainly mangroves, seagrass meadows and tidal salt marshes. Most of it sits in waterlogged sediments, where low oxygen slows decomposition and lets carbon accumulate over long periods.
Why it matters
Per hectare, blue carbon ecosystems can store several times more carbon than many terrestrial forests, largely below ground. They are also being lost to aquaculture, coastal development and erosion. Protecting and restoring them delivers climate benefits plus coastal protection, fisheries and livelihoods, which buyers value as co-benefits.
How blue carbon is measured
- Biomass: tree measurements with mangrove-specific allometric equations, including roots.
- Soil carbon: sediment cores to a defined depth (often 1 m or more), with bulk density and carbon content measured in the lab.
- Accretion and loss: sediment deposition and erosion rates.
- Other gases: methane in low-salinity areas, and nitrous oxide where relevant.
Verra’s VM0033 covers tidal wetland and seagrass restoration. Projects fall under the WRC category, sometimes combined with ARR for mangrove planting.
Indonesia angle
Indonesia has the largest mangrove area of any country and extensive seagrass meadows. Large areas of former mangrove were converted to shrimp and fish ponds, many now abandoned, which creates restoration opportunities. National policy treats mangrove rehabilitation as a priority, and coastal land tenure involves multiple authorities. See blue carbon policy in Indonesia. Seagrass carbon remains harder to credit because measurement is more complex.
Common mistakes
- Planting mangroves in the wrong tidal zone, leading to low survival.
- Counting only trees and ignoring soil carbon, or the reverse.
- Using terrestrial allometric equations for mangroves.
- Ignoring community use of coastal land and fisheries.
- Promising credits before tenure over coastal land and ponds has been confirmed with the relevant forestry, marine and village authorities.
Related terms
See mangrove, seagrass and WRC, or explore the blue carbon hub.
Frequently asked questions
Why is blue carbon important?
Coastal ecosystems store large amounts of carbon per hectare, mostly in waterlogged soils that can accumulate carbon for centuries. When cleared, they release it quickly.
Can blue carbon generate carbon credits?
Yes. Mangrove and tidal wetland restoration and conservation can earn credits under methodologies such as Verra VM0033 and other programmes' blue carbon methods.