Blue Carbon: Mangroves, Seagrass and Tidal Wetlands

Updated 2026-11-02 · 4 min read · By the akar.earth specialist team

Blue carbon in Indonesia: how mangrove, seagrass and tidal wetland projects work under VM0033, soil carbon measurement, pond rehabilitation and policy.

Blue carbon is the carbon stored by mangroves, seagrass meadows and tidal wetlands, most of it in waterlogged soils that can hold it for centuries. Indonesia has the largest mangrove area of any country, so mangrove restoration and conservation are among its most important carbon project types.

This hub explains how blue carbon projects work, how they differ from forest projects on land, what VM0033 requires, and what Indonesian policy means for developers and coastal communities.

Why blue carbon is different

A mangrove stand holds carbon in trunks, branches and roots, like any forest. The difference is below ground. Tidal flooding keeps the soil waterlogged and low in oxygen, so organic matter decomposes very slowly and builds up over long periods. In many mangroves the soil stock is larger than the tree stock.

That has three consequences for projects:

• Big stocks per hectare. Conversion of mangroves, especially to aquaculture ponds, releases soil carbon as well as biomass carbon.
• Measurement is harder. You need soil cores, bulk density and carbon content, not only tree inventories. See measuring mangrove soil carbon.
• Hydrology decides success. Planting seedlings where tides do not reach, or on mudflats that were never mangrove, fails. Restoration works when water flow is restored first.

Mangrove vs terrestrial forest carbon compares the two side by side.

A mental model: water, sediment, trees, people

Project types

Mangrove restoration. Re-establishing mangroves on degraded or converted land. Abandoned shrimp and fish ponds are the main opportunity in Indonesia, because their hydrology can often be restored by breaching pond walls. Rehabilitating abandoned aquaculture ponds to mangrove covers the engineering and tenure questions. Mangrove restoration carbon projects step by step covers the full project cycle.

Mangrove conservation. Protecting existing mangroves from conversion. This works like REDD+, with a baseline of expected loss. See the REDD+ hub.

Seagrass. Seagrass meadows store carbon in sediment, but measurement, additionality and permanence are harder to prove. Seagrass carbon: science and crediting limits explains why seagrass credits remain rare.

Peat and tidal wetlands. Coastal peat swamps sit between blue and green carbon. Rewetting drained peat is covered in the REDD+ hub and by peatland protection rules.

The methodology: VM0033

Verra’s VM0033 covers tidal wetland and seagrass restoration. It accounts for biomass, soil carbon and, where relevant, methane and nitrous oxide emissions that can offset some of the soil gains in lower-salinity sites. It also requires projects to consider sea-level rise and sediment supply when estimating long-term carbon. Check the current version and applicability conditions on the Verra website before designing a project.

Community-focused projects sometimes use Plan Vivo, which emphasises local governance and benefit sharing. Co-benefit labels such as CCB are common, because mangroves protect coasts and support fisheries.

Species

Indonesian mangroves are species-rich, and species zone by elevation and salinity. The species section profiles five common restoration species:

• Rhizophora apiculata and Rhizophora mucronata, the most planted genus, often overused.
• Avicennia marina, a pioneer on seaward and disturbed sites.
• Bruguiera gymnorrhiza and Sonneratia alba, which fill other zones.

Mixed-species planting that matches natural zonation tends to survive better than monoculture Rhizophora rows.

Indonesian policy

Mangrove rehabilitation has been a national priority, and blue carbon touches several ministries: forestry for mangroves inside the forest estate, marine affairs for coastal and seagrass areas, and local government for spatial planning. Carbon trading sits under Perpres 110/2025, with exchange-traded units recorded in SRUK. Permenhut 6/2026 covers forestry carbon trading, including community participation. Blue carbon policy in Indonesia maps which rules apply where. The Indonesian regulation hub covers the wider framework.

Measurement and monitoring

Blue carbon monitoring combines soil coring, tree plots, elevation surveys and remote sensing of canopy extent. Survival counts after planting matter: a restoration site that loses most seedlings in the first year will not deliver its ex-ante estimate. Drone imagery and RTK-surveyed plots make change easier to verify in tidal sites where access is difficult. The dMRV hub covers these tools in general.

Common mistakes

• Planting on mudflats. Bare mudflats and seagrass beds are often not former mangrove. Planting there tends to fail and can damage other habitats.
• Ignoring pond tenure. Abandoned ponds may still have owners or users who expect compensation or a role in the project.
• Skipping soil data. Without soil cores, the largest carbon pool goes unmeasured, and conservative defaults may undervalue the project.
• Counting seedlings, not survival. Planted numbers make good headlines, but credits depend on trees that survive and grow.
• Overlooking methane. In lower-salinity sites, methane can offset part of the soil gain and must be accounted for.

Getting started

1. Map historical mangrove extent and current land use, especially ponds.
2. Check tenure: ponds are often held privately even when the land sits in the forest estate.
3. Assess hydrology before choosing species.
4. Design soil and biomass sampling before planting.

Our field data campaigns cover RTK plot mapping, drone surveys and soil sampling for coastal sites. Every blue carbon page is listed below.