MCC-F01 Blue Carbon Sequestration — Methodologies M001 (Mangrove), M002 (Seagrass), M003 (Salt Marsh)

Instrument: Methodology texts under MCC-200 Methodology Framework v2.0 Section 3 (MOD-01–MOD-10, cl. 0023–0038), for the three F01 codes that the registry carried as APPROVED without a text (SC-2026-001). Tier 4: Standards Committee approval with peer review and 30 days' public consultation (MCC-001 cl. 0082; MCC-200 cl. 0109). Status: CANDIDATE v0.1 — 26 August 2026. NOT APPROVED. Prepared by the programme administration as commissioned by GB-2026-001 Resolution 4.2, for peer review and public consultation. Until adopted, M001–M003 remain UNDER REVIEW and no project may be registered against them. Structure: one family core (Part I, modules shared under MCC-200 cl. 0035) and one methodology sheet per code (Part II) carrying the ecosystem-specific parameters. A methodology is the core plus its sheet. Basis: MCC-100 v2.2 cl. 0167 (MCC-CC), 0183.1 (100-year horizon, 30-year post-crediting monitoring), 0186–0193 (buffer, reversals); MCC-200 v2.0 cl. 0031.1, 0031.3; F01 Blue Carbon Guidance v1.0 as corrected by Guidance Errata No. 1 (Parts B and C); Buffer Pool Management Policy v1.0; ESS Policy v1.0 (eight principles); Definitions Register v1.0. External references: IPCC 2013 Wetlands Supplement (Ch. 4, coastal wetlands); Verra VM0033 v2.1 (tidal wetland and seagrass restoration) for structure and defaults where MCC has none.

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Part I — F01 family core

MOD-01 Applicability

01.1 Scope. Removals of CO₂ from the atmosphere by the establishment, restoration or enhancement of blue-carbon vegetation and the accumulation of organic carbon in vegetated coastal sediments, and the avoided loss of existing blue-carbon stocks where a documented threat exists. The unit is MCC-CC: one tonne CO₂e removed or reduced (MCC-100 cl. 0167). No other unit may be issued under F01 (Errata C1).

01.2 Ecosystems. M001 mangrove; M002 seagrass; M003 salt marsh and tidal wetland. Kelp (former M004) is retired (FD-2026-08-24 D14) and is not covered.

01.3 Eligible activities. (a) Restoration: re-establishing the ecosystem on an area where it existed and was lost or degraded — hydrological restoration, planting or transplanting, substrate stabilisation, removal of stressors. (b) Enhancement: measurably increasing carbon stock density on an existing degraded stand. (c) Conservation (avoided loss): protecting an existing stand against a documented, quantified threat. Activities that convert another natural ecosystem (mudflat, sandflat, natural lagoon, other wetland) into the target ecosystem are not eligible (F01 Guidance §2; no land-use change into blue carbon).

01.4 Conditions. All of the following, evidenced in the PDD (MCC PDD Template v1.1, Section A–C):

1. Ecosystem type present or historically present within the project boundary, evidenced by field survey, time-series imagery or herbarium/sediment record.
2. Minimum area met (sheet §1); non-contiguous parcels may be aggregated if each parcel is ≥ 20 % of the minimum and all are under one management plan.
3. Tenure and use rights sufficient to bind the area for the 30-year contractual commitment of MCC-200 cl. 0031.3, with landowner notice-of-intent-to-convert clause.
4. Baseline quantifiable under MOD-02 (a zero baseline is not permitted).
5. Additionality demonstrated under MOD-02.
6. Monitoring capacity in-house or contracted for the crediting period and the 30-year post-crediting period.
7. Host-country position recorded (MCC-100 cl. 0102–0122; D8): notification for contribution-basis units, authorisation where a corresponding adjustment is sought.
8. FPIC and the eight ESS principles addressed under MOD-09.

01.5 Geographic scope. Global, intertidal and shallow subtidal; sheet §1 sets depth and salinity limits per ecosystem.

MOD-02 Baseline and additionality

02.1 Baseline scenario. The most plausible carbon-stock trajectory of the project area in the absence of the project, over the crediting period, for each stratum (stand of like condition), determined from: current stock (measured), documented drivers of change (time-series imagery ≥ 10 years, cadastral and permit records, local land-use plans, interviews), and regional loss or recovery rates. Three baseline types:

• B-stable: no evidenced threat and no natural recovery → stock constant. Default for any existing stand for which a threat is not documented (Errata C4(d)).
• B-loss: evidenced ongoing loss at rate L (Mg C ha⁻¹ yr⁻¹) → stock declines until exhausted; the rate may not be applied beyond the year the stock reaches zero (Errata B7).
• B-recovery: natural recovery would occur without the project (e.g. after a stressor was removed by others) → the project may claim only the increment above natural recovery.

02.2 Additionality. Investment or barrier analysis per MCC-100 cl. 0060–0068: the applicant identifies the financial, technical, institutional or legal barrier that MCC revenue removes, shows the activity is not required by law, and shows it is not common practice in the region (≤ 20 % of comparable sites in the last 10 years). For conservation (avoided loss), additionality additionally requires that the threat be independent of the applicant and that protection was not already funded.

02.3 The rule that decides what is creditable. Only the difference between the project stock trajectory and the baseline trajectory is creditable, stratum by stratum. Growth on a stand the project does not act on, or whose baseline is B-stable, is not creditable even if it occurs (Errata C4(d)).

MOD-03 Quantification

03.1 Carbon pools. Above-ground biomass (AGB), below-ground biomass (BGB), dead wood and litter (M001 only, optional, conservative to omit), and soil organic carbon (SOC) to 1 m depth in two layers (0–30 cm, 30–100 cm). A pool may be excluded if its exclusion is conservative (it increases in the project and is omitted) — never if it decreases.

03.2 Net removals in year t, per stratum s:

ΔC_proj,s,t = Σ_pools (C_pool,s,t − C_pool,s,t−1) — the measured or modelled stock change under the project ΔC_base,s,t = the stock change under the baseline of MOD-02 (zero for B-stable; −L·A until exhaustion for B-loss; +R·A for B-recovery) NR_t = Σ_s (ΔC_proj,s,t − ΔC_base,s,t) × 44/12

All carbon in Mg C; conversion 44/12 = 3.667 to t CO₂e (Errata B7); 1 Mg = 1 t.

03.3 Stock caps. Modelled accumulation stops at the reference stock of a mature stand of the same ecosystem and setting (sheet §3); modelled loss stops at zero (Errata B7). No rate is extrapolated past the cap.

03.4 Non-CO₂ gases. CH₄ and N₂O emissions from restored areas are estimated with IPCC 2013 Wetlands Supplement defaults by salinity class and deducted (in t CO₂e, GWP100 AR5: CH₄ 28, N₂O 265). Sites with salinity < 18 ppt must measure or apply the high-emission default. Emissions from project activities (fuel, nursery operations) are deducted where > 1 % of gross removals.

03.5 Tiers. Tier 1: IPCC / regional defaults for stock and rate, no site measurement — permitted only for the PDD estimate, not for issuance. Tier 2: measured baseline stocks, default rates — permitted for issuance with the Tier 2 uncertainty treatment. Tier 3: measured stocks and site-derived rates (site allometry, chronosequence or repeat measurement) — required for any project > 500 ha or claiming > 5,000 t CO₂e yr⁻¹.

03.6 Uncertainty. The project reports the 90 % confidence interval of NR_t from a Monte Carlo (≥ 1,000 draws) or analytical propagation of the sampling, allometric, bulk-density and carbon-content errors. The creditable quantity is the lower bound (10th percentile). Where the half-width of the interval exceeds 30 % of the mean, the shortfall in sampling must be corrected before the next verification.

03.7 Leakage. Activity displacement (fishing, wood cutting, grazing, aquaculture) and market effects are assessed under MCC-100 cl. 0125–0130. Leakage is quantified in absolute terms (t CO₂e yr⁻¹) outside the boundary and deducted after the uncertainty discount, not multiplied into it (Errata C2). A project whose leakage exceeds 30 % of gross removals is not creditable until redesigned.

03.8 Issuable quantity.

Issuable_t = (NR_t at the 10th percentile − Leakage_t − ProjectEmissions_t) × (1 − b)

where b is the project's buffer contribution under MOD-08 (10–40 %, set per project by the Buffer Pool Management Policy). Negative NR_t in any year is carried forward and netted before any further issuance.

03.9 Ex-ante vs ex-post. No unit is issued on modelled growth. Issuance follows verification of measured stock change (MOD-07). Ex-ante estimates in the PDD are estimates.

MOD-04 Monitoring

04.1 Design. Permanent plots in a stratified random design, stratum = ecosystem × condition class × restoration cohort. Minimum plot density per sheet §4; never fewer than 10 plots per stratum. Plots are geo-referenced (± 3 m), marked, and re-measured in the same season each cycle.

04.2 Parameters and frequency.

Parameter	Frequency	Method	Precision target
Area and cover of the ecosystem	Annual	Satellite/drone imagery ≥ 3 m, ground-truthed; polygon change ≤ 5 % without field check	± 5 % area
AGB (and BGB by root:shoot ratio)	Annual (M001 biennial after year 5)	Sheet-specific allometry or shoot density × biomass	± 10 %
SOC 0–30 and 30–100 cm	Every 2 years (baseline, then biennial)	Cores at ≥ 30 % of plots; bulk density + LOI/elemental analysis; depth-corrected	± 20 % of stock
Survival / shoot density (restoration cohorts)	Quarterly year 1–2, then annual	Fixed quadrats	—
Hydrology / salinity / water quality	Continuous logger or monthly	Site instruments	—
Disturbance events (storm, cutting, dieback, anchoring)	Continuous, reported within 30 days	Patrol log, imagery	—
Leakage indicators (activity outside boundary)	Annual	Transects and interviews outside the boundary	—
Non-CO₂ flux (if measured)	Seasonal	Chambers	—

04.3 Post-crediting period. For 30 years after the last issuance (MCC-200 cl. 0031.1): area and cover annually by remote sensing; AGB and SOC at 5-year intervals; any reversal reported under MCC-100 cl. 0191 with the buffer consequences of the Buffer Policy.

04.4 Quality. Calibrated instruments, chain-of-custody for samples, accredited laboratory for carbon content, raw data retained ≥ 10 years and made available to the VVB. Monitoring reports follow MCC-100 Annex B (v1.1 when adopted).

MOD-05 Reporting

Annual monitoring report (Annex B) within 90 days of the monitoring-period end, in English, published in the registry at verification. Contents: stratum map and areas, plot data summary, stock estimates with confidence intervals, baseline comparison, leakage assessment, non-CO₂ estimate, disturbance log, safeguards indicators, SD indicators (reported, never credited), declarations and file hashes. Stakeholder communication: a plain-language summary to affected communities in the local language within the same 90 days.

MOD-06 Validation

Scope per MCC-100 cl. 0153 and MCC-400 art. 63, using the Validation Report Template v1.0 when adopted: applicability (MOD-01), baseline evidence and additionality (MOD-02), quantification design and tier justification (MOD-03), monitoring plan adequacy (MOD-04), permanence and buffer risk assessment (MOD-08), safeguards and FPIC (MOD-09), host-country regulatory compatibility (MCC-200 cl. 0082, 0086), double-counting prevention (cl. 0077). Site visit mandatory. VVB accredited for F01 under MCC-400 with a Lead Auditor holding coastal-ecology or soil-science competence (art. 23).

MOD-07 Verification

Frequency: first verification after ≥ 12 months of monitoring, then annual or biennial at the project's election (biennial permitted only when the previous two verifications closed without material findings). Scope per MCC-100 cl. 0154 and MCC-400 art. 64, Verification Report Template v1.0: re-measurement of ≥ 10 % of plots by the VVB, recomputation of NR_t, leakage and non-CO₂, confirmation of the buffer rate, recommended issuance volume. Materiality 5 % of the claimed quantity. Peer review inside the VVB before the opinion.

MOD-08 Permanence and risk management

08.1 Horizon. 100-year permanence horizon; 30-year post-crediting monitoring; 30-year binding contractual commitment with landowner notice-of-intent-to-convert (MCC-200 cl. 0031.1, 0031.3; MCC-100 cl. 0183.1).

08.2 Buffer. The project's buffer contribution b is set by the risk assessment of the Buffer Pool Management Policy v1.0 within 10–40 % (MCC-100 cl. 0186–0188), verified by the VVB. Family reference value 20 %. Risk factors weighed: tenure security, governance and enforcement, financial sustainability of the 30-year commitment, exposure to sea-level rise and storm surge, hydrological dependence on upstream works, disease and dieback history, community support. Phased release: 25 % of the accumulated buffer at year 15 and 50 % at year 30 of the project (Buffer Policy release schedule), conditional on no unremedied reversal.

08.3 Reversal. Loss > 10 % of the verified stock in any 12 months, or > 20 % over the crediting period, is a reversal (MCC-100 cl. 0191): the project reports within 30 days, the buffer is drawn down for the lost quantity, and further issuance is suspended until the cause is addressed and a re-measurement verified. Intentional reversal (conversion) triggers the contractual remedies and the compensation obligation of cl. 0193.

08.4 Sea-level rise. Every PDD includes a landward-migration assessment for the relevant SLR scenarios (IPCC SSP2-4.5 and SSP5-8.5 to 2100); where the ecosystem cannot migrate, the risk score and b reflect it.

MOD-09 Safeguards and co-benefits

The eight principles of the ESS Policy v1.0 (cl. 0011–0045) apply (Errata B1). F01-specific (MCC-200 cl. 0095): habitat disruption during works, species displacement (including from planting monocultures — mixed native species required for M001; no non-native species in any code), livelihood impacts on coastal users, access to fishing grounds and gleaning areas. FPIC from indigenous peoples and local communities before registration, documented under the ESS Policy. Co-benefits (fish nursery function, shoreline protection, water quality) are reported under the Sustainable Development Contribution Framework and are not encoded in the unit (Errata C1).

MOD-10 Registry and claims

Units are serialised under MCC-800 v1.1 as MCC-CC with methodology code, vintage year, stratum and verification reference. Claims follow the Claims Policy v1.1: a retirement supports a contribution claim; a compensation or offset claim requires the host-country authorisation and corresponding adjustment recorded under MCC-100 cl. 0102–0122. Double counting: the project declares any other crediting programme, and the registry records the declaration (MCC-200 cl. 0077).

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Part II — Methodology sheets

MCC-M001 — Mangrove Restoration and Conservation (v0.1 CANDIDATE)

1. Applicability. Mangrove forest (true mangrove species per the regional flora) in the intertidal zone. Minimum area 10 ha. Salinity 5–40 ppt; sites < 18 ppt apply the CH₄ default of MOD-03.4. Restoration by hydrological repair is preferred over planting; planting-only projects must show why hydrology is not the limiting factor. Aquaculture-pond reversion is eligible if the pond was mangrove within the last 50 years and tenure allows permanent conversion back. 2. Pools. AGB, BGB (root:shoot 0.49 default, IPCC Wetlands Supplement Table 4.5), dead wood (optional), SOC to 1 m. 3. Quantification parameters. AGB by species-specific or regional allometry (DBH and height; Komiyama et al. 2005 as the default pan-tropical equation). Reference mature stock caps unless measured locally: AGB+BGB ≤ 120 Mg C ha⁻¹ (wet tropics) / 60 (dry tropics and subtropics); SOC ≤ 250 Mg C ha⁻¹ to 1 m unless measured. Default Tier 2 rates: biomass accumulation 2.5 Mg C ha⁻¹ yr⁻¹ (years 1–20, then declining linearly to zero at the cap); SOC accumulation 1.5 Mg C ha⁻¹ yr⁻¹ (IPCC Wetlands Supplement Table 4.12 range, conservative end). Baseline loss rate for B-loss strata from measured time series; if only regional data exist, ≤ 3 Mg C ha⁻¹ yr⁻¹ and never past exhaustion. 4. Monitoring. Plots 0.04 ha (20 × 20 m), ≥ 10 per stratum and ≥ 1 per 10 ha; DBH ≥ 2.5 cm and height annually years 1–5, biennially after; SOC cores at ≥ 30 % of plots biennially; cover by imagery annually. 5. Risks weighed for b. Cutting pressure, pond re-conversion, sediment starvation from upstream dams, SLR migration space, cyclone exposure, disease. 6. Worked example. The corrected mangrove example of Guidance Errata No. 1 C4 (Case 1: 165 t CO₂e yr⁻¹ issuable on 140 ha with 20 ha restored; Case 2: 412 t yr⁻¹ with a documented threat) is the reference calculation for this sheet.

MCC-M002 — Seagrass Meadow Restoration (v0.1 CANDIDATE)

1. Applicability. Seagrass meadows (e.g. Posidonia, Zostera, Thalassia, Enhalus, Halodule) in shallow subtidal and low intertidal waters to 15 m depth (deeper only with Tier 3 measurement). Minimum area 5 ha. Eligible activities: transplanting (shoots, seeds, sods), stressor removal (mooring management, water-quality improvement with documented causal link), sediment stabilisation, and conservation of an existing meadow under documented threat (anchoring, trawling, dredging, eutrophication). 2. Pools. AGB and BGB (rhizome and roots; BGB often exceeds AGB), SOC to 1 m. Biomass is a small, fast-cycling pool; SOC is the creditable pool for most projects and its accumulation must be measured, not defaulted, from the second verification. 3. Quantification parameters. Biomass from shoot density × per-shoot biomass (species-specific, site-measured). SOC accumulation default Tier 2: 0.5 Mg C ha⁻¹ yr⁻¹ (global seagrass mean, conservative; Posidonia matte may justify more with Tier 3 cores). Reference SOC cap 150 Mg C ha⁻¹ to 1 m unless measured (Posidonia matte higher with measurement). Restoration cohorts are not creditable until cover ≥ 50 % of the reference meadow density in two consecutive surveys. Baseline loss for B-loss strata from imagery or acoustic mapping time series. 4. Monitoring. Cover and extent by acoustic or drone/satellite mapping annually (turbid sites: diver transects); shoot density and biomass in ≥ 10 fixed 0.25 m² quadrats per stratum seasonally in years 1–2, then annually; SOC cores (≥ 50 cm, to 1 m where possible) biennially at ≥ 30 % of stations; water quality (turbidity, nutrients) monthly; boat traffic and anchoring events logged. 5. Risks weighed for b. Eutrophication, heat waves and marine heat wave dieback, storm burial, anchoring and trawling enforcement, sediment resuspension, disease (Labyrinthula). 6. Worked example. 40 ha transplanted Zostera meadow reaching 60 % cover by year 3; SOC accumulation measured at 0.6 Mg C ha⁻¹ yr⁻¹ from year 4 (10th percentile 0.45): NR = 40 × 0.45 × 3.667 = 66 t CO₂e yr⁻¹; leakage none (no displaced activity); CH₄ negligible at 30 ppt; b = 25 % → 50 t CO₂e yr⁻¹ issuable. The example shows why seagrass projects are aggregated: the unit yield per hectare is low and the fixed monitoring cost is not.

MCC-M003 — Salt Marsh and Tidal Wetland Conservation and Rehabilitation (v0.1 CANDIDATE)

1. Applicability. Salt marsh and brackish tidal wetland (halophytic graminoids and herbs) in the intertidal zone; managed realignment (removal or breaching of sea walls to re-establish tidal inundation) is the principal restoration activity. Minimum area 2 ha. Salinity ≥ 18 ppt for the low-CH₄ default; brackish sites measure or apply the high default. Realignment projects account for the loss of any terrestrial soil carbon on the flooded land (deducted where the pre-project land carried a carbon stock that oxidises or erodes). 2. Pools. AGB (small; annual turnover), BGB, SOC to 1 m. SOC is the creditable pool; biomass is monitored for condition, and may be credited only where a persistent increase is measured. 3. Quantification parameters. SOC accumulation default Tier 2: 1.0 Mg C ha⁻¹ yr⁻¹ for realigned or restored marsh in the first 20 years (IPCC Wetlands Supplement Table 4.12 range, conservative end), declining to the site's reference accretion-driven rate thereafter; reference SOC cap 200 Mg C ha⁻¹ to 1 m unless measured. Allochthonous carbon: where sediment supply is high, the project measures the fraction of accumulated carbon that is autochthonous (δ¹³C or equivalent) and credits only the autochthonous fraction unless the allochthonous carbon would otherwise have been mineralised (evidence required). Baseline loss for B-loss strata from erosion/retreat rates in imagery or LiDAR. 4. Monitoring. Elevation and accretion by surface elevation tables or marker horizons (≥ 3 per stratum) annually; vegetation cover and species composition in ≥ 10 fixed 1 m² quadrats per stratum annually; SOC cores biennially at ≥ 30 % of stations; tidal inundation and salinity by logger; creek network and edge retreat by imagery annually. 5. Risks weighed for b. Coastal squeeze (no landward migration), erosion at the marsh edge, sediment supply, sea-wall integrity upstream, grazing management, nutrient loading. 6. Worked example. 30 ha managed realignment; pre-project arable land with 40 Mg C ha⁻¹ soil carbon, of which 20 % is lost in the first 5 years (deducted: 30 × 8 = 240 Mg C over 5 years = 176 t CO₂e yr⁻¹ for years 1–5); marsh SOC accumulation measured at 1.2 Mg C ha⁻¹ yr⁻¹ (10th percentile 0.9) from year 3: 30 × 0.9 × 3.667 = 99 t CO₂e yr⁻¹. Years 1–5 net ≈ negative (carried forward); from year 6, 99 t yr⁻¹, b = 20 % → 79 t CO₂e yr⁻¹ issuable until the carried-forward deficit is cleared. The example shows why realignment projects must model the terrestrial-carbon loss honestly before promising early units.

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Open questions for peer review (MCC-200 cl. 0004, 0043)

1. Whether the default Tier 2 rates in each sheet should be replaced by regional tables (IPCC Wetlands Supplement Ch. 4 by climate zone) in Annex form before adoption.
2. Whether conservation (avoided loss) under F01 should require Tier 3 baseline evidence in every case, given Errata C4(d).
3. Whether the 30 % leakage ceiling of MOD-03.7 should be lower for conservation projects.
4. Treatment of allochthonous carbon (M003 §3) — accept the conservative autochthonous-only rule, or adopt the VM0033 approach.
5. Whether kelp (retired M004) should return as a separate candidate once a permanence basis exists.

Change log — v0.1 CANDIDATE (26 Aug 2026): first issue, commissioned by GB-2026-001 Resolution 4.2. Not approved; not for use in any PDD.