Why seagrass matters more than most people think
By Brian Muchiri
Nairobi, Kenya – When discussions turn to climate mitigation, seagrass rarely features. Yet along Kenya’s coastline, these underwater flowering plants execute what billions in climate technology aspires to achieve: extracting carbon dioxide from the atmosphere and securing it for millennia.
Seagrasses are marine flowering plants that inhabit shallow coastal waters. Unlike algae or seaweed, they possess roots, stems, leaves and produce seeds. They form dense underwater meadows that stabilise sediments, filter pollutants and provide nursery habitat for juvenile fish. These meadows underpin fisheries worth thousands of dollars per hectare annually, supplying protein and income to coastal communities across East Africa.
Their most significant function, however, is carbon storage. Seagrass meadows capture and store carbon at rates rivalling tropical forests, then lock it in sediments where decomposition barely occurs. This capacity, termed “blue carbon” in climate policy, positions seagrass as a critical component of how coastal nations meet Paris Agreement commitments.
As carbon markets develop and pressure intensifies to identify cost-effective climate solutions, seagrass is transitioning from ecological curiosity to economic asset. Whether this attention secures these ecosystems or creates exploitation mechanisms for dependent communities remains contested.
Distribution along Kenya’s coast
Kenya’s seagrass beds cover approximately 317 square kilometres, distributed across three primary zones: the northern coast around Lamu Archipelago, the central coast near Mombasa and Kilifi, and the southern approaches to the Tanzania border.
The plants favour shallow, sheltered areas where coral reefs attenuate ocean swells and permit sediment settlement. The most extensive beds appear in protected lagoons and creek systems including Gazi Bay, Mida Creek and the intertidal flats surrounding Lamu. Most thrive between the low tide mark and six-metre depths, where sufficient light penetrates for photosynthesis.
Twelve seagrass species inhabit Kenyan waters. In sandy, wave-exposed areas, Thalassia hemprichii anchors through thick rhizomes. In sheltered, muddier locations, Thalassodendron ciliatum forms dense monospecific stands. The large-leafed Enhalus acoroides, with leaves exceeding one metre, occupies deeper waters in channels and reef edges.
Many locations support mixed meadows where five to seven species coexist, each occupying distinct niches. Some excel at sediment stabilisation through dense root networks. Others optimise nutrient cycling or provide structural habitat for invertebrates.
These seagrass beds function within interconnected coastal systems alongside mangrove forests and coral reefs. Nutrients circulate between these ecosystems. Juvenile fish raised in seagrass meadows later populate coral reefs. Organic matter from mangroves fertilises seagrass beds. This connectivity means protecting one ecosystem typically requires protecting all three.
For fishing communities, this interconnection represents intuitive knowledge. Traditional management systems in locations such as Lamu historically included seasonal closures to permit recovery.
Blue carbon sequestration science
The carbon storage capacity of seagrass is exceptional, with these ecosystems accounting for approximately 10 per cent of all carbon buried annually in ocean sediments despite covering less than 0.2 per cent of the ocean floor.
During photosynthesis, seagrass absorbs dissolved carbon dioxide from seawater. Some carbon builds plant tissues: roots, rhizomes, leaves. Unlike terrestrial plants where most carbon eventually returns to the atmosphere through decomposition, seagrass traps carbon in sediments where decomposition virtually ceases.
The mechanism operates through elegant simplicity. Seagrass meadows reduce water velocity, causing suspended particles to settle. Dense root and rhizome networks trap this sediment. Meanwhile, the plants produce organic matter that incorporates into the seafloor. Over time, this creates thick deposits of carbon-rich sediment extending several metres deep.
Anaerobic conditions in these sediments prove critical. Without oxygen, decomposition slows dramatically. Carbon that might cycle back to the atmosphere within decades in terrestrial systems remains locked away for centuries or millennia. Core samples from Mediterranean seagrass beds have dated some carbon deposits to over 4,000 years old.
Per unit area, seagrass meadows can sequester carbon up to 35 times faster than tropical forests. Research in Gazi Bay measured carbon storage rates of approximately 55,000 kilogrammes per hectare in healthy mixed meadows. Sediment organic carbon stocks ranged from 160.7 to 233.8 megagrammes of carbon per hectare across four dominant species.
Across Kenya’s seagrass coverage, this represents substantial annual carbon sequestration equivalent to removing approximately 70,000 cars from operation annually.
This storage system depends entirely on keeping seagrass and sediments undisturbed. When meadows suffer damage or destruction, stored carbon does not simply stop accumulating. It begins escaping.
Threats from coastal development and pollution
Kenya’s seagrass meadows face accelerating degradation from multiple vectors.
Seagrass coverage in Kenya has declined at 0.85 per cent annually since 1986, with losses accelerating from 0.29 per cent annually in 2000 to 1.59 per cent by 2016. This trajectory has released substantial stored carbon.
Coastal development ranks among the most destructive forces. Port expansion, particularly the Lamu Port-South Sudan-Ethiopia-Transport corridor project, raises concerns regarding impacts on surrounding marine ecosystems including extensive seagrass meadows supporting local fishing communities. Dredging operations destroy seagrass beds directly whilst stirring sediments that smother nearby areas. Construction of jetties, marinas and coastal infrastructure frequently treats seagrass beds as vacant space rather than functioning ecosystems.
Tourism development creates subtler pressures. Hotels and resorts often discharge inadequately treated wastewater. Beach seine fishing, popular in tourist areas, involves repeatedly dragging weighted nets across the seafloor, uprooting seagrass and compacting sediments. Anchor damage from boats, particularly in unregulated moorings, creates bare patches requiring years for recovery.
Agricultural runoff extends impacts beyond farmland. During rainy seasons, fertilisers, pesticides and sediments flow into coastal waters. Nutrient loading triggers algal blooms that block sunlight required for photosynthesis. Near urban centres such as Mombasa, untreated or partially treated sewage compounds nutrient pollution whilst introducing pathogens and heavy metals.
Overfishing compounds problems through non-obvious pathways. When herbivorous fish such as rabbitfish and parrotfish are overharvested, algae they normally graze can overgrow seagrass leaves, blocking light and outcompeting plants. Bottom trawling, though illegal in many coastal areas, continues and physically tears up meadows whilst resuspending toxic sediments.
Climate change itself threatens ecosystems that could help mitigate it. Rising water temperatures stress seagrasses, increasing vulnerability to disease. Ocean acidification affects calcium-dependent processes. More intense storms physically damage meadows. Sea level rise could benefit some seagrass by expanding shallow habitat, but only where coastal development has not hardened shorelines and prevented landward migration.
The feedback loop proves particularly concerning. When seagrass dies or suffers disturbance, sediment carbon does not remain buried. Exposed sediments release carbon dioxide back into water and atmosphere, transforming a carbon sink into a carbon source, with global seagrass loss potentially releasing up to 299 million tonnes of carbon dioxide annually.
Kenya Marine and Fisheries Research Institute monitoring data shows measurable declines in seagrass coverage near major urban centres and development zones. Some areas around Mombasa have lost 30 to 40 per cent of seagrass coverage since the 1990s.
These losses often remain invisible. Seagrass degradation occurs underwater, out of policymaker and public view. By the time impacts become visible through declining fish catches or increased coastal erosion, damage is typically extensive and expensive to reverse.
Restoration projects and potential carbon credits
Growing recognition of blue carbon value is generating conservation action, though whether this translates to genuine protection or merely commodifies nature remains hotly debated.
Several restoration initiatives operate along the Kenyan coast. In Gazi Bay, community groups supported by KMFRI are replanting degraded seagrass areas. The approach combines scientific expertise with traditional ecological knowledge. Local fishers help identify areas where seagrass previously thrived and understand current and sediment flow patterns affecting survival.
The Wasini Beach Management Unit initiated seagrass restoration efforts in 2014 after receiving training from KMFRI, and has restored one hectare of seagrass meadows, planting at least 10,000 seedlings.
Protected experimental plots demonstrate seagrass can recover relatively quickly when threats are removed. In areas closed to fishing and boat traffic, natural recolonisation occurs within five to ten years. Active replanting can accelerate this, though success rates vary significantly depending on site selection, species choice and ongoing maintenance.
The Mikoko Pamoja project in Gazi Bay pioneered the community-based blue carbon model in Kenya. Launched in 2013, it became the world’s first blue carbon initiative to successfully sell carbon credits from mangrove conservation activities. Since 2014, the community has received KES 2.6 million (USD 20,000) over two years, with revenue flowing directly to community development projects including water infrastructure, scholarships and healthcare facilities.
Extending this model to seagrass represents the next frontier, with at least 300 hectares of seagrass beds in Vanga Bay planned for protection by local communities, with carbon credits to be sold through voluntary markets using the Plan Vivo system.
The economics appear compelling. Restoring one hectare of seagrass could generate carbon credits worth hundreds of dollars annually in perpetuity, potentially exceeding income from short-term exploitation.
Significant obstacles remain. Carbon credit certification requires baseline assessments, continuous monitoring and verification that carbon storage is additional, meaning it would not have occurred without the project. For seagrass, this proves technically complex and expensive. Measuring sediment carbon stocks at depth, accounting for natural variability and monitoring over decades requires technical capacity and funding few coastal communities possess independently.
More fundamentally, questions persist regarding beneficiaries and cost bearers. Carbon rights in Kenya’s coastal waters remain legally ambiguous. If carbon credits generate substantial revenue, will it flow to fishing communities whose livelihoods depend on these ecosystems, or will it be captured by project developers, NGOs or government entities? History suggests that without careful safeguards, local communities often end up displaced or restricted from traditional fishing grounds in the name of conservation that primarily benefits distant interests.
Critics question whether carbon credits constitute the appropriate framework. They argue this approach permits wealthy nations and corporations to continue polluting whilst purchasing offsets from the Global South, a form of carbon colonialism that fails to reduce net emissions. For seagrass conservation to serve climate justice, they contend it must be embedded in broader strategies that secure resource rights for coastal communities, fund genuine adaptation to climate impacts they did not cause and demand emissions reductions at source rather than offset schemes.
Practical enforcement challenges exist. Seagrass beds lack fences. Protection requires managing multiple human activities across landscapes and seascapes: controlling pollution from distant farms, regulating coastal development, enforcing fishing restrictions, managing tourism. Carbon credits might fund some of this, but they do not constitute a comprehensive solution for complex governance challenges.
The status quo proves unsustainable. Kenya’s seagrass meadows face accelerating threats whilst providing undervalued services: carbon storage, fish habitat, coastal protection, water filtration. Whether through carbon markets, government protection or community management, these ecosystems require urgent investment and policy attention.
The question is whether recognition arrives in time. Seagrass growing beneath shallow coastal waters demonstrates that powerful climate solutions need not be high-tech innovations but rather protection and restoration of natural systems that have regulated planetary climate for millions of years.
This explainer connects to our Natural Capital category for coverage of carbon offset policy and international climate finance mechanisms. Related UN Sustainable Development Goals: SDG 13 (Climate Action), SDG 14 (Life Below Water), SDG 15 (Life on Land).
