Understanding Blue Carbon Wetlands

Blue carbon wetlands represent one of nature's most efficient climate solutions, though they often go unrecognised in broader environmental discussions about climate change and carbon sequestration. These special ecosystems—primarily mangroves, saltmarshes, and seagrass meadows—are distinguished by their remarkable ability to capture and store atmospheric carbon.

What Is Blue Carbon?

"Blue carbon" refers to the carbon captured and sequestered by coastal and marine ecosystems. Unlike terrestrial forests that primarily store carbon in their biomass, blue carbon ecosystems also trap carbon within their waterlogged sediments, where it can remain locked away for millennia if left undisturbed.[1][2] This long-term storage capacity makes these wetlands particularly valuable for climate mitigation strategies and efforts to enhance carbon sinks worldwide.[3]

The Three Key Blue Carbon Wetlands

Mangroves

Mangroves thrive in tropical and subtropical intertidal zones, characterised by their distinctive root systems that trap sediment and create carbon-rich soils. A single hectare of tropical mangrove forest can store up to 1,000 tonnes of CO2 - equivalent carbon,[4] with studies suggesting that mangroves are able to store up to five times more organic carbon than tropical forests per unit area.[5] Their complex root structures not only accumulate carbon but also create habitat for countless marine species, serving as crucial nurseries for juvenile fish and invertebrates. Mangroves also provide coastal protection, reducing the impact of sea-level rise and extreme weather events linked to climate change.[6]

Saltmarshes

Saltmarshes occupy temperate coastlines worldwide, featuring salt-tolerant grasses and shrubs that accumulate carbon through their extensive root networks. Despite their unassuming appearance, they can sequester carbon at rates exceeding terrestrial ecosystems.[7] Saltmarshes also play a critical role in nutrient cycling, transforming excess nitrogen from agricultural runoff into less harmful forms before it reaches open water, thereby improving coastal water quality.[8] [9]

Seagrass Meadows

Seagrass meadows grow in shallow marine environments, forming vast underwater prairies that capture carbon through photosynthesis and trap organic material within their dense vegetation. These meadows can sequester carbon up to 35 times faster than tropical rainforests when measured on a per-area basis,[10] and their sediments never become carbon-saturated.[11] Their extensive root systems also help to stabilise seafloor sediments, preventing the release of ancient carbon deposits and supporting overall oceanic carbon storage.

Why Blue Carbon Matters

These blue carbon wetlands collectively cover less than 0.2% of the ocean area yet account for approximately half of all carbon sequestered in ocean sediments.[12] [13] This remarkable efficiency makes blue carbon ecosystems among the most carbon-dense and efficient carbon sequestration landscapes on Earth.

Beyond carbon storage, blue carbon wetlands provide critical ecosystem services including:

• Protecting coastlines and coastal communities from storm surges and erosion by absorbing wave energy

• Filtering water pollutants, enhancing marine ecosystem health and improving coastal water quality

• Supporting marine biodiversity, including numerous endangered and commercially important species

• Sustaining fisheries that feed millions globally and support coastal economies

• Providing recreational, tourism and cultural benefits for coastal communities

Threats and Conservation Opportunities

Despite their ecological importance, blue carbon wetlands face alarming rates of destruction—we have lost ~55% of the world’s wetlands since 1900 alone[14] and continue to lose 1-2% annually to coastal development, aquaculture expansion, pollution, and climate impacts.[15] This destruction not only eliminates future carbon sequestration potential but can release centuries' worth of stored carbon back into the atmosphere, exacerbating climate change.

The economic value of blue carbon ecosystems extends far beyond carbon storage. When factoring in all ecosystem services, a healthy mangrove forest can provide benefits worth up to ~AUD$ 300,000 per hectare annually.[16] [17] This realisation has sparked increased interest in blue carbon markets and carbon offset projects, where conservation efforts can be financed through the sale of verified carbon credits.

As coastal communities face mounting climate-related threats, blue carbon wetlands offer a rare win-win solution—simultaneously addressing climate change while building resilience against its impacts. Prioritising these ecosystems in conservation planning will be crucial for both climate-change mitigation and climate adaptation strategies in the decades ahead.

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References

[1] Mitsch, W.J., Bernal, B., Nahlik, A.M., Mander, U., Zhang, L., Anderson, C.J., Jørgensen, S.E., and Brix, H., 2013. Wetlands, carbon, and climate change. Landscape Ecol, 28, p.583–597, doi: 10.1007/s10980-012-9758-8.

[2] Kelleway, J.J., Saintilan, N., Macreadie, P.I., Baldock, J.A., Heijnis, H.,  Zawadzki, A., Gadd, P., Jacobsen, G., and Ralph, P.J., 2017. Geochemical analyses reveal the importance of environmental history for blue carbon sequestration, J. Geophys. Res. Biogeosci., 122, doi: 10.1002/2017JG003775.

[3] Serrano, O., Lovelock, C.E., B. Atwood, T. et al., 2019. Australian vegetated coastal ecosystems as global hotspots for climate change mitigation. Nat Commun, 10, doi: 10.1038/s41467-019-12176-8.

[4] Wang, M., Zhang, T., Xie, Y., Zhang, Z., and Wu, X., 2025. Mapping accumulated carbon storage of global mangroves from 2000 to 2020 at a 1 km resolution. Sci Data, 12, doi:10.1038/s41597-025-04881-5.

[5] Donato, D.D., Kauffman, J.B., Murdiyarso, D., Kurnianto, S., Stidham, M., and Kanninen, M., 2011. Mangroves among the most carbon-rich forests in the tropics. Nature Geoscience, 4, p.293-297, doi:10.1038/ngeo1123.

[6] Duarte, C.M., Losada, I.J., Hendriks, I.E., Mazarrasa, I., and Marbà, N., 2013. The role of coastal plant communities for climate change mitigation and adaptation. Nature Climate Change, 3, p.961-968, doi:10.1038/nclimate1970.

[7] McLeod, E., Chmura, G.L., Bouillon, S., Salm, R., Bjork, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H. and Silliman, B.R., 2011. A blue print for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO_2. Front. Ecol. Environ., 9(10), p.552-560, doi: 10.1890/110004.

[8] McLeod, E., Chmura, G.L., Bouillon, S., Salm, R., Bjork, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H. and Silliman, B.R., 2011. A blue print for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO_2. Front. Ecol. Environ., 9(10), p.552-560, doi: 10.1890/110004.

[9] Nelson, J.L., and Zavaleta, E.S., 2012. Salt Marsh as a Coastal Filter for the Oceans: Changes in Function with Experimental Increases in Nitrogen Loading and Sea-Level Rise. PLOS One, 7(8), doi: 10.1371/journal.pone.0038558.

[10] Macreadie, P.I., Baird, M.E., Trevathan-Tackett, S.M., Larkum, A.W.D., and Ralph, P.J., 2014. Quantifying and modelling carbon sequestration capacity of seagrass meadows – A critical assessment. Marine Pollution Bulletin, 83, p.430-439, doi: 10.1016/j.marpolbul.2013.07.038.

[11] McLeod, E., Chmura, G.L., Bouillon, S., Salm, R., Bjork, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H. and Silliman, B.R., 2011. A blue print for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO_2. Front. Ecol. Environ., 9(10), p.552-560, doi: 10.1890/110004.

[12] Serrano, O., Lovelock, C.E., B. Atwood, T. et al., 2019. Australian vegetated coastal ecosystems as global hotspots for climate change mitigation. Nat Commun, 10, doi: 10.1038/s41467-019-12176-8.

[13] Duarte, C. M., Middelburg, J.J., and Caraco, N. 2005. Major role of marine vegetation on the oceanic carbon cycle. Biogeosciences. 2, doi: 10.5194/bg-2-1-2005.

[14] Davidson, N.C., 2014. How much wetland has the world lost? Long-term and recent trends in global wetland area. Marine and Freshwater Research, 65(10), p.934-941, doi: 10.1071/MF14173.

[15] Convention on Wetlands 2021. Global Wetland Outlook: Special Edition 2021. Gland, Switzerland: Secretariat of the Convention on Wetlands.

[16] de Groot, R., Brander, L., van der Ploeg, S., Costanza, R., Bernard, F., Braat, L., Christie, M., Crossman, N., Ghermandi, A., Hein, L., Hussain, S., Kumar, P., McVittie, A., Portela, R., Rodriguez, L.C., ten Brink, P., and van Beukering, P., 2012. Global estimates of the value of ecosystems and their services in monetary units. Ecosystem Services, 1(1), p.50-61, doi:10.1016/j.ecoser.2012.07.005.

[17] Original figure of USD 200,000 adjusted for purchasing power parity.