Recognising the urgent need for nature-based carbon removal solutions, this article explores why kelp forests remain missing from formal “blue carbon” frameworks and what new evidence tells us about their potential.
Kelp forests stretch along coastlines worldwide, forming vast underwater habitats. They capture carbon dioxide through photosynthesis, but their importance goes far beyond this. Kelp forests create shelter for countless marine species, help cycle nutrients, and improve water quality, making them vital to the health of coastal ecosystems and a promising ally in tackling climate change.
Yet kelp forests are still missing from official “blue carbon” frameworks, which currently focus on habitats with soils that clearly lock carbon away, such as mangroves, salt marshes, and seagrasses (Hurd, 2022). This gap is not because kelp lacks potential, but because it is harder to measure how much carbon is stored and for how long (Hurd, 2022). Growing evidence, however, shows that kelp does contribute to long-term carbon storage, even if the processes are more complex to track.
Kelp carbon has often been overlooked because it is harder to measure than in soil- or sediment-based systems. Mangroves, salt marshes and seagrass trap carbon in sediments, where it can accumulate for centuries, but kelp grows on rocky coasts and has no roots to store carbon in place (Hurd, 2022). Instead, kelp biomass is shed into the surrounding water throughout its short lifespan, typically only a few years, and in some species less than one. This rapid turnover means much of the material is quickly recycled within coastal ecosystems, making long-term storage less obvious compared with terrestrial plants that build up wood or soils.
Confusion with seaweed farming has contributed to the complexity. In annual aquaculture systems, seaweed is harvested and the associated carbon is quickly released back to the atmosphere when consumed or decomposed (Hurd, 2022). These systems differ fundamentally form perennial kelp forests, which maintain standing biomass and continuously export material.
Perspectives also vary across regions. Japan has gone further than most by formally recognising kelp and other seaweeds as part of its blue carbon strategy, even creating a government-approved “J-Blue Credit” scheme that issues carbon credits from kelp restoration and farming projects. These credits have been traded at relatively high prices, showing strong market interest. In contrast, researchers in places like Australia have been more cautious, stressing the uncertainties around how much kelp carbon can be stored and for how long. In practice, however, many marine carbon removal approaches face the same challenge and also rely on modelling to estimate long-term sequestration. For example, ocean alkalinity enhancement, where crushed minerals are added to seawater to lock away CO₂ through chemical reactions. This means kelp is often judged by stricter standards than other emerging solutions, even though the uncertainties are similar.
Despite these challenges, kelp carbon is essential to consider. Kelp forests fringe roughly a third of the world’s coastlines, making them one of the planet’s most widespread coastal ecosystems. They generate vast amounts of organic carbon that is continually released into the ocean.
Recent field data are beginning to show how large kelp’s contribution could be. For example, a new study in northern Portugal estimated that local kelp forests store 16.5 Gg of carbon in their biomass and sequester around 1,900 Mg C yr⁻¹, accounting for about one-third of Portugal’s total annual blue carbon sequestration despite covering less area than salt marshes (Franco et al., 2025). When normalised by area, the kelp forests sequestered carbon at rates equal to or higher than seagrasses and salt marshes, underscoring their potential if included in blue carbon strategies.
On a global scale, modelling indicates that around 15% of seaweed forest production (about 56 Tg of carbon per year) is exported beyond the continental shelf, with a portion remaining sequestered for centuries (Filbee-Dexter et al., 2024). While this is only around 0.5% of annual fossil fuel emissions, it is still a major natural carbon flux, comparable to other recognised blue carbon ecosystems like salt marshes and seagrasses, and one of the few marine pathways we can actively enhance through conservation and restoration. Field studies also show that high-latitude kelp forests channel nearly all their production into detritus, much of which is exported (Pedersen et al., 2020).
In addition to particulate material, kelp releases dissolved organic carbon (DOC) while alive. A significant share of this DOC is chemically stable and resistant to breakdown, with around 58% persisting over long timescales (Li et al., 2022). Recent work has shown that brown algae exude complex compounds such as fucoidan, which can endure in sediments for centuries (Buck-Wiese et al., 2023). This demonstrates that even living kelp forests and farms contribute to long-lived carbon pools.
Where kelp occurs over depositional seabeds, further storage can occur through burial in underlying sediments. Measurements beneath kelp farms confirm accumulation of organic carbon, with burial rates increasing with farm age and in some cases comparable to recognised blue carbon habitats (Duarte et al., 2024).
These pathways show the ecosystem-scale potential of kelp. Natural kelp forests maintain standing biomass year-round, while cultivation of perennial species can also contribute to continuous carbon cycling. Beyond carbon, kelp ecosystems deliver important co-benefits. They absorb nutrients, raise oxygen levels, and reduce harmful algal blooms, improving water quality and supporting healthier coastal ecosystems (Jiang et al., 2020). For carbon markets, however, not all sequestration is equal, credits must reflect carbon that is both measurable and long-lasting. Recognising which kelp pathways offer permanence is key to ensuring kelp is fairly included alongside other blue carbon ecosystems.
New evidence is clarifying kelp’s role in carbon removal, both in wild forests and in cultivation systems. Recent field studies and pilot monitoring efforts have shown that kelp can contribute measurable carbon flows through several pathways. For example, dissolved organic carbon (DOC) released while kelp is alive includes a fraction that resists microbial breakdown and can persist for centuries (Li et al., 2022; Buck-Wiese et al., 2023). Sediment burial has also been documented beneath kelp canopies and cultivation sites, with accumulation rates depending on local hydrodynamics and substrate type (Duarte, 2023; Duarte et al., 2024). Together, these findings suggest kelp can contribute to long-term carbon storage, even though the magnitude varies widely by site.
Beyond carbon, kelp ecosystems also deliver well-documented co-benefits. In wild coastal settings, kelp forests help buffer nutrient loads, raise oxygen levels, and reduce the risk of harmful algal blooms, supporting healthier marine communities (Jiang et al., 2020). Some experimental work on kelp cultivation has shown similar effects, though outcomes depend heavily on scale and design; large monoculture farms, for instance, may not deliver the same ecological benefits and can raise concerns around biodiversity.
Where kelp currently lags behind other blue carbon ecosystems is in crediting systems. Mangroves, salt marshes, and seagrasses already have established MRV protocols that allow them to generate internationally recognised credits. For kelp, no equivalent framework yet exists. Japan’s J-Blue Credit scheme is an exception, but it applies only domestically and highlights the absence of international standards. Elsewhere, kelp carbon removal remains at the stage of research trials, without a clear route into global carbon markets.
Debates also continue around attribution and permanence. Some critiques focus on attribution: whether the carbon locked away by kelp can be shown to have originally come from the atmosphere. This is challenging because atmospheric CO2 must first dissolve into surface waters before kelp can absorb it, and that exchange takes time. Others emphasise permanence: whether the carbon from kelp stays stored for centuries or eventually returns to the atmosphere. These are distinct but often confused issues. Early monitoring work suggests that canopy-forming kelps can lower CO2 levels in surface waters, speeding up the exchange of carbon from the air into the ocean, and that a small but important fraction of exported kelp material does remain stored on long timescales. Together, this shows that kelp could deliver measurable, lasting carbon removal if robust monitoring systems are developed.
Kelp forests are a highly productive but historically overlooked part of blue carbon. Evidence shows they contribute to long-term carbon storage through dissolved organic carbon, particulate export, and in some settings, sediment burial. Just as importantly, kelp forests deliver major co-benefits: they improve water quality, support marine biodiversity, and provide habitat that underpins coastal food webs. In many ways, carbon can be seen as an added incentive to restore these ecosystems and the life they support.
Conserving natural forests and developing perennial cultivation systems that complement them should be priorities. Any future crediting of kelp carbon must be based on rigorous standards: clear atmospheric attribution, long-term permanence (typically at least 100 years), exclusion of harvested biomass, and safeguards against double counting. Quantification will also require modelling to track dispersal and sequestration processes that cannot be directly observed. Taken together, these findings support kelp carbon as an essential, though complex, component of natural climate solutions.
Kelp forests are missing from blue carbon frameworks
Despite covering roughly a third of the world’s coastlines and storing carbon through multiple pathways, kelp is excluded from formal blue carbon policy because its carbon is dispersed rather than stored in soils, making it harder to measure.
They export carbon through several long-lived pathways
Kelp contributes to ocean carbon sinks via particulate material that can be buried in sediments or sink to the deep sea, and via dissolved organic carbon (DOC)—including a stable fraction (rDOC) that can persist for centuries.
Monitoring remains the main barrier to recognition
Unlike mangroves and seagrasses, kelp lacks established MRV protocols to quantify how much atmospheric carbon it removes and how long it stays stored. Early studies are showing promise, but international frameworks are still needed.
Beyond carbon, kelp offers major co-benefits
Restoring kelp forests would also boost biodiversity, improve water quality, and support fisheries, meaning carbon can be seen as an added incentive to protect and restore these vital ecosystems.
Unlocking the power of kelp