Seagrass meadows store carbon in a form that is easily overlooked. Unlike forests, where much of the carbon is held above ground in visible biomass, approximately 90% of the carbon associated with a seagrass ecosystem lies below ground, in soils that accumulate over centuries and, in places, millennia^1,2. Provided the meadow above remains intact, that carbon stays locked away. When a meadow is dredged, buried beneath sediment or lost to coastal development, it is released. For countries seeking to account for coastal ecosystems within their climate commitments, this below-ground store is therefore the pool of primary interest – and, until recently, the pool about which least was known across much of Southeast Asia^1,2.

The difficulty is that carbon storage is highly site-specific. Reported stocks vary up to 45-fold between seagrass habitats, depending on species composition, sediment characteristics, water depth and disturbance history³. Global average values, while useful for preliminary estimates, cannot substitute for national measurement when governments are determining whether and how to include seagrass in national greenhouse gas inventories, Nationally Determined Contributions (NDCs) or emerging carbon finance mechanisms^4,13. 

To address this gap, the CMS Office – Abu Dhabi, under the framework of the Dugong Memorandum of Understanding (MOU), supported a coordinated blue carbon assessment through the Seagrass Ecosystem Services (SES) project (2020-2026), funded by the International Climate Initiative (IKI) of the German Federal Government. Technical partner Edith Cowan University (Australia) worked with four national partner organizations – YAPEKA in Indonesia, The MareCet Research Organization in Malaysia, Community Centered Conservation (C3) in the Philippines and Save Andaman Network (SAN) in Thailand – to deliver the first regionally comparable assessment of seagrass blue carbon in Southeast Asia^5-8. 

A Common Framework, Four National Assessments 

Rather than four independent studies, the project applied a single standardized protocol at every site, so that differences in the results would reflect genuine environmental variation rather than differences in method. Field teams collected sediment cores from healthy reference meadows, from meadows subject to identified pressures and – in Thailand – from a restored meadow. Cores were analyzed for bulk density, organic matter content and organic carbon concentration, with selected samples dated to establish rates of carbon accumulation^5-8. Each national partner led the fieldwork in its own country, supported by training and technical guidance from Edith Cowan University. 

Figure 1. A YAPEKA team member measures a sediment core in a seagrass meadow in North Minahasa, Indonesia, with mangrove forest along the shoreline behind. Cores were taken to a depth of one meter, the depth used in most carbon verification schemes because it represents the soil likely to be affected by disturbance. Photo: YAPEKA, reproduced from Lavery et al. (2023)⁵ under CC BY-NC-SA. 

The four assessments are summarized in Table 1. Each is published in full and openly accessible. 

Table 1. Summary of the four national blue carbon assessments undertaken under the SES project. Avoided emissions potential refers to the emissions prevented by protecting a healthy meadow from disturbance. 1 Mg = 1 tonne. Sources: references ^5-8. 

Two features of the table warrant attention. The first is the range: stocks measured under an identical protocol differed approximately fifty-fold between the lowest site in Johor and the highest in Sangihe^5,6. The second is what the table cannot show. In two countries, rates of carbon accumulation could not be determined at all, and in the remaining two only long-term rates were obtained^5-8. That absence is itself among the project’s most policy-relevant findings. 

Four Assessments, Four Lessons 

Although every country applied the same scientific approach, each assessment surfaced a distinct lesson about translating blue carbon science into conservation practice. Taken together, they describe the conditions under which seagrass can realistically enter national climate accounting. 

Indonesia – Capacity determines what can be measured 

The meadows of North Minahasa and the Sangihe Islands proved to hold some of the highest seagrass carbon stocks recorded anywhere in the world. The assessment nonetheless could not be completed as designed. No national laboratory was equipped to undertake the required elemental carbon and radioisotope analyses, and authorization to export samples for analysis abroad was not granted. Carbon content had to be estimated indirectly, and rates of carbon accumulation could not be established. Rods installed in the meadows to measure sediment accumulation directly were removed and repurposed by local fishers, and travel restrictions during the COVID-19 pandemic replaced planned in-person training with online instruction^5,9. 

What this means: laboratory capability, permitting pathways and community agreement are not supporting activities that sit around a blue carbon assessment; they determine its scope. Where the objective is data of inventory quality, the analytical pathway should be secured before fieldwork begins. High-quality cores from these meadows remain in storage awaiting analysis, and completing that work would close a significant national data gap at modest cost⁵. The evidence generated has nonetheless supported the designation of seagrass meadows within provincial marine spatial planning in North Sulawesi (RZWP3K) and Indonesia’s preparations to include seagrass in its Second NDC⁵. 

Malaysia – Carbon crosses habitat boundaries 

Stable carbon isotope analysis of the Johor sediments showed that much of the carbon stored beneath the seagrass was not fixed by the seagrass at all. Mangrove detritus from adjacent forests is the most probable source. Malaysia also produced the project’s one successful low-cost calibration, establishing a reliable local relationship between organic matter content and organic carbon that allows carbon to be estimated using only a muffle furnace and a balance – equipment within reach of institutions that cannot access elemental analysers^6,10,11. 

What this means: mangroves, seagrasses and tidal wetlands function as a connected system, and managing or crediting them separately misstates both the benefit of protection and the risk of loss. Conservation planning and carbon accounting should therefore operate at the scale of the coastal seascape10. Malaysia’s voluntary carbon market currently admits seagrass restoration but not seagrass conservation; this evidence base offers a foundation for addressing that gap⁶. 

Figure 2. The intertidal meadow at Setindan Island, Johor, fully exposed at low tide, with vegetated islands beyond. Isotope analysis indicated that much of the carbon stored beneath meadows such as this originated in neighbouring mangrove forests rather than in the seagrass itself. Photo: MareCet, reproduced from Lavery et al. (2023)⁶ under CC BY-NC-SA. 

The Philippines – Ecological condition is not a proxy for carbon value 

In Roxas, Palawan, the results inverted expectations. The reference meadow held the lowest carbon stock of the four sites assessed, while a meadow subject to fishing and boating pressure held nearly twice as much. The explanation appears to lie in meadow structure and catchment setting rather than in condition as conventionally assessed: the reference site comprises dense but patchy seagrass, while stocks elsewhere are raised by sediment and organic inputs from the San Nicolas River and the adjacent settlement⁷. 

What this means: meadows cannot be ranked by carbon value on inspection, nor by the presence of a named pressure. They must be measured. It follows that meadows classified as degraded may still hold carbon stocks worth protecting – a consideration for prioritization exercises that routinely set them aside. It also confirms that blue carbon assessments must account for the surrounding catchment and land use, not the meadow alone^3,7. 

Figure 3. Patches of disturbed seagrass at San Nicolas, Roxas, Palawan, at the mouth of the San Nicolas River. Sites affected by river-borne sediment held higher carbon stocks than the reference meadow, indicating that catchment inputs can outweigh local disturbance in determining what a meadow stores. Photo: C3, reproduced from Lavery et al. (2023)⁷ under CC BY-NC-SA. 

Thailand – Protection delivers more than restoration 

Trang provided one of the few opportunities anywhere to sample a restored seagrass meadow of sufficient age. Carbon storage at the restored site at Boon Kong Bay was comparable to that of the healthy reference meadow – an encouraging result, though one accompanied by considerable uncertainty. Set against this, the assessment found that protecting an intact meadow avoids emissions of 48–134 tonnes of CO₂-equivalent per hectare, whereas restoration adds sequestration of up to 33 kilograms per hectare per year⁸. 

What this means: restoration is a complementary measure, appropriate where degradation has already occurred, but it is not a substitute for protecting meadows that remain intact. Where resources are limited, protection should be sequenced first^8,12. Thailand’s Voluntary Emission Trading Scheme already contains a seagrass methodology covering both biomass and soil carbon, under which no projects have yet been registered; the conservative, locally derived values from this assessment provide a defensible starting point for developing them⁸. 

Figure 4. The restored meadow at Boon Kong Bay, Trang, Thailand, where transplanting of Enhalus acoroides began in 2007. Restored meadows of sufficient age are rarely available for sampling, making this one of the few sites worldwide where the recovery of carbon storage could be tested directly. Photo: Save Andaman Network, reproduced from Lavery et al. (2023)⁸ under CC BY-NC-SA. 

Constraints Common to All Four Countries 

Three obstacles recurred across every assessment and will shape blue carbon implementation in the region more widely^5-8. 

• Rates of carbon accumulation remain largely unquantified. Short-term accumulation rates – the parameter most carbon crediting schemes require – could not be established in any of the four countries, owing variously to local sediment conditions, export restrictions and permitting delays^5-8,9. Direct measurement using surface elevation markers is the most promising alternative, but only where the installations are agreed with the communities using the site. 

• Permitting is a first-order project risk. Requirements for field sampling and sample export delayed or prevented key analyses in three of the four countries. Permitting sequences should be mapped, and realistic time budgeted, at the design stage^5,7,8. 

• Remote training has limits. All four reports record that the shift from in-person to online instruction, necessitated by the pandemic, reduced both the efficiency and the quality of the work. Face-to-face field and laboratory training should be treated as a core requirement of capacity development^5-8. 

Implications for Policy and Practice 

• National measurement is a prerequisite. Global default values cannot support the country-specific emission factors required for higher-tier reporting under the IPCC Wetlands Supplement¹³. 

• Methods must be validated where they are applied. A technique that performed well in Malaysia failed in Thailand^6,8. Standardized protocols enable comparison; they do not guarantee transferability. 

• Account at seascape scale. Carbon moves between mangroves, seagrasses and tidal wetlands, and accounting frameworks that treat them as discrete units will misattribute both credit and risk10. 

• Invest in enabling conditions. Laboratories, permitting systems, trained personnel and community agreement determined what could be measured. They warrant investment as infrastructure, not as project overhead^5-8,13. 

Beyond the carbon figures themselves, the project leaves four national organizations able to design, execute and interpret a blue carbon assessment, together with a candid record of where the methods proved difficult^5-8. The same meadows that hold this carbon also support inshore fisheries, stabilize coastlines, maintain water quality and provide the principal food source for the dugong (Dugong dugon), listed as Vulnerable on the IUCN Red List14. Their protection therefore advances climate, biodiversity and coastal livelihood objectives simultaneously. 

Further Reading 

The four technical reports are published open access by Edith Cowan University under a Creative Commons license, and contain the full methodology, site descriptions, national policy review and lessons learnt. 

• Blue Carbon Opportunities: North Minahasa and Sangihe Island, Indonesia – Lavery et al. (2023), with YAPEKA. 

• Blue Carbon Opportunities: Johor and Penang, Malaysia – Lavery et al. (2023), with The MareCet Research Organization. 

• Blue Carbon Opportunities: Roxas, Palawan, The Philippines – Lavery et al. (2023), with Community Centered Conservation. 

• Blue Carbon Opportunities: Trang, Thailand – Lavery et al. (2023), with Save Andaman Network. 

• The full regional dataset is openly available: SEAS Blue — The IKI SES Project SE Asian Blue Carbon Dataset. 

• Practical guidance for field teams is provided in the Seagrass Blue Carbon Toolkit. 

References 

1. Nellemann, C. et al. (2009) Blue Carbon: The Role of Healthy Oceans in Binding Carbon. Arendal: UNEP/GRID-Arendal.
2. Duarte, C.M., Losada, I.J., Hendriks, I.E., Mazarrasa, I. & Marbà, N. (2013) ‘The role of coastal plant communities for climate change mitigation and adaptation’, Nature Climate Change, 3, pp. 961–968.
3. Lavery, P.S., Mateo, M.-Á., Serrano, O. & Rozaimi, M. (2013) ‘Variability in the carbon storage of seagrass habitats and its implications for global estimates of blue carbon ecosystem service’, PLoS ONE, 8(9), e73748.
4. Fourqurean, J.W. et al. (2012) ‘Seagrass ecosystems as a globally significant carbon stock’, Nature Geoscience, 5, pp. 505–509.
5. Lavery, P., Lafratta, A., Digdo, A.A., Dandoro, A.A., Septiani, C., Cahyono, T., Serrano, O. & Masqué, P. (2023) Blue Carbon Opportunities: seagrass carbon storage and accumulation rates at North Minahasa and Sangihe Island, Indonesia. Technical Report for the IKI Seagrass Ecosystem Services Project. Edith Cowan University and YAPEKA. https://doi.org/10.25958/hd9h-aj79
6. Lavery, P.S., Lafratta, A., Nair, D., Ponnampalam, L., Ng, J.E., Fairul Izmal, J.H., Serrano, O. & Masqué, P. (2023) Blue Carbon Opportunities: seagrass carbon storage and accumulation rates at Johor and Penang, Malaysia. Technical Report for the IKI Seagrass Ecosystem Services Project. Edith Cowan University and The MareCet Research Organization. https://doi.org/10.25958/zfxg-0y62
7. Lavery, P.S., Lafratta, A., Caabay, J.M., Ramilo, R., Garay, H.G., Daquioag, M., Serrano, O. & Masqué, P. (2023) Blue Carbon Opportunities: seagrass carbon storage and accumulation rates at Roxas, Palawan, The Philippines. Technical Report for the IKI Seagrass Ecosystem Services Project. Edith Cowan University and Community Centred Conservation. https://doi.org/10.25958/z907-cc31
8. Lavery, P.S., Lafratta, A., Palahan, R., Sanlee, M., Stankovic, M., Panyawai, J., Serrano, O. & Masqué, P. (2023) Blue Carbon Opportunities: seagrass carbon storage and accumulation rates at Trang, Thailand. Technical Report for the IKI Seagrass Ecosystem Services Project. Edith Cowan University and Save Andaman Network. https://doi.org/10.25958/p8vr-zv31
9. Arias-Ortiz, A. et al. (2018) ‘Reviews and syntheses: ²¹⁰Pb-derived sediment and carbon accumulation rates in vegetated coastal ecosystems – setting the record straight’, Biogeosciences, 15, pp. 6791–6818.
10. Kennedy, H. et al. (2010) ‘Seagrass sediments as a global carbon sink: isotopic constraints’, Global Biogeochemical Cycles, 24, GB4026.
11. Howard, J., Hoyt, S., Isensee, K., Pidgeon, E. & Telszewski, M. (eds) (2014) Coastal Blue Carbon: Methods for assessing carbon stocks and emissions factors in mangroves, tidal salt marshes, and seagrass meadows. Arlington, VA: Conservation International, IOC-UNESCO and IUCN.
12. Macreadie, P.I. et al. (2021) ‘Blue carbon as a natural climate solution’, Nature Reviews Earth & Environment, 2, pp. 826–839.
13. IPCC (2014) 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands. Geneva: IPCC.
14. Marsh, H., O’Shea, T.J. & Reynolds, J.E. (2011) Ecology and Conservation of the Sirenia: Dugongs and Manatees. Cambridge: Cambridge University Press.