Blue Carbon Credits: Mangroves, Seagrass and Coastal Wetlands

Most of the carbon in a mangrove forest is not in the trees. It sits in the waterlogged mud beneath them, sometimes metres deep, where low oxygen keeps dead roots and leaves from rotting for centuries. That buried store is what makes coastal ecosystems so valuable for the climate, and it is also what makes blue carbon credits harder to measure than almost any other kind.

"Blue carbon" covers mangroves, seagrass meadows, tidal salt marshes and, in some definitions, coastal peatlands. India has a long mangrove coastline, from the Sundarbans in West Bengal to the Gulf of Kachchh in Gujarat and the Godavari–Krishna delta in Andhra Pradesh, and national programmes such as MISHTI have put mangrove planting firmly on the policy agenda.

How the credits are created

Blue carbon projects come in two broad kinds:

• Restoration. Replanting mangroves on mudflats where they have been lost, or restoring the natural flow of tides to wetlands cut off by embankments and ponds. As the ecosystem recovers, it draws down carbon into biomass and sediment.
• Conservation. Protecting existing mangroves or wetlands that are under real threat, typically from conversion to shrimp ponds, salt pans or ports. Credits represent emissions avoided by preventing that loss.

Measurement combines tree surveys with sediment cores. Teams take cores at sample points, analyse carbon content and density in the laboratory, and estimate how much has accumulated or been protected. Remote sensing tracks the area of cover over time. Methodologies under Verra, for example its tidal wetland and seagrass restoration method, set out how this should be done, and an independent verifier checks the results before the registry issues credits.

What a buyer gets

Restoration projects produce removals. Conservation projects produce avoidance credits. Some projects do both on different parts of the site. The project type field on the listing tells you which you are looking at, and the difference matters if your climate plan counts removals separately.

The main quality questions

Measurement uncertainty

Sediment carbon varies a lot across short distances, and soil depth assumptions can make a large difference to the total. Ask how many cores were taken, to what depth, and whether default values from the methodology were used in place of site data. Conservative defaults are not a weakness; generous ones are.

Permanence on a moving coastline

Coastal sites face cyclones, erosion, changes in river sediment and rising seas. Mangroves can often keep pace with slow sea-level rise by trapping sediment, but not everywhere. As with forestry, the standards hold back a share of credits in a buffer pool, sized to the assessed risk. Ask what that share is and whether the project has a plan for storm damage. Survival rates of planted seedlings, which can be low in the first years, are another useful indicator.

Baseline realism for conservation

For avoided-loss projects, the credit rests on the claim that the area would otherwise have been cleared. That claim should rest on evidence: historic loss rates nearby, permit applications, aquaculture expansion in the district. If a mangrove belt is already legally protected and enforced, avoided-loss credits are hard to justify. Our page on additionality, permanence and leakage explains how baselines are tested.

Tenure and community rights

Coastal land in India often has layered ownership: state forest departments, revenue land, panchayats and customary fishing rights. A project needs clear agreement on who holds the carbon rights and how local fishing and farming families share in the income. Projects that rely on community labour for planting and patrolling succeed far more often when those communities are paid fairly and consulted from the start.

Co-benefits

This is where blue carbon tends to stand out. Mangroves act as a storm buffer for villages behind them, serve as nurseries for fish and crabs that support local catches, filter coastal water and shelter birds. SDG tiles on these listings often include Life Below Water (SDG 14), Life on Land (SDG 15) and Climate Action (SDG 13), sometimes with Gender Equality (SDG 5) where women's groups run nurseries. Ask for evidence behind each tile, such as household income data or fish catch surveys; our page on SDGs and co-benefits suggests what to look for.

What to ask the seller

Is this restoration, conservation, or both?

The answer decides whether you are buying removals or avoidance, and which risks matter most. Ask for the split by volume if the project does both.

How was the sediment carbon measured?

Request the sampling design, number and depth of cores, and whether site data or defaults were used. The verification report should summarise this.

What share of credits goes to the buffer, and have there been losses?

A reversal after a cyclone, and how it was handled, tells you a lot about the developer.

Who holds the carbon rights, and how do communities benefit?

Look for written agreements with the landholder and a benefit-sharing plan in the project documents.

For forward lots, when are issuances expected?

Restoration projects take years to show measurable gains. Our guide to spot, issued and forward credits covers the trade-offs.

On this marketplace

Blue carbon supply is small compared with forestry or renewables, and good projects are often spoken for early. Look through the Blue Carbon category, and if nothing current fits, post your requirement on our buyer intake form so we can match you as new lots come in.