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Pichavaram mangrove forest, Tamil Nadu. Image Source: Sakthibalan via Wikimedia Commons
Along India’s coast, mangroves live at the boundary between land and sea, where freshwater, tides, sediments and saltwater meet. Their tangled roots hold soils together, provide habitat for fish and other species, support coastal livelihoods and help protect communities from storms and floods. They also perform another function that is becoming increasingly important as countries seek nature-based responses to climate change: they store carbon.
Mangrove ecosystems are among the most carbon-dense forest ecosystems in the world. Their waterlogged, oxygen-poor environments slow decomposition, allowing substantial amounts of carbon to accumulate in vegetation and soils. Globally, mangrove ecosystems are estimated to store between 4.4 and 11.7 petagrams of carbon. Yet estimating how much carbon India's mangroves hold is not straightforward.
A recent study titled 'Mangrove biomass and carbon storage in India: Implications for blue carbon potential' authored by S Anathakrishnan and others and published in Biomass Futures that reviews biomass-derived carbon storage across India's major mangrove systems finds substantial differences between regions. Species composition, salinity, tidal conditions, sediment availability, freshwater inflow, forest age and human disturbance all influence how much biomass mangroves accumulate and where that carbon is stored.
The findings point to the need for more region-specific and context-specific carbon accounting. Without it, using a single representative carbon value for India's mangroves could obscure substantial differences between ecosystems and affect the way their contribution to climate mitigation is assessed.
Mangroves include trees, shrubs, ferns and palms that grow along the boundary between land and sea, generally between the high and low tide marks. Their roots are regularly exposed to saline water and can also receive freshwater through surface runoff and flooding.
These ecosystems draw nutrients from tidal waters, freshwater flows and coastal soils and sediments deposited from surrounding land through erosion. Their importance extends beyond carbon.
Mangrove forests support the food security and livelihoods of coastal communities and provide ecosystem services estimated at $1.6 billion each year. Their habitats provide feeding and breeding grounds for crabs, prawns, snails, fish, birds, reptiles and mammals. They also provide resources such as firewood, timber, cattle feed, honey and medicines.
Mangroves can help protect groundwater aquifers from seawater intrusion and contribute to the removal of coastal pollution, including toxic heavy metals. Their dense vegetation also provides protection against natural hazards such as tsunamis, storms and floods. For communities living along the coast, therefore, mangroves are closely linked to water, livelihoods and protection from environmental hazards.
Mangroves store carbon in different parts of their biomass. Above ground biomass includes all living vegetation, such as stems, branches, leaves, bark and reproductive structures. Below ground biomass consists primarily of living roots and other plant structures beneath the soil.
Both are measured as oven-dry weight per unit area and are important for understanding carbon storage and ecosystem dynamics. The waterlogged conditions in which mangroves grow are particularly important. Oxygen-poor environments slow decomposition, allowing carbon to remain stored in vegetation and sediments for long periods. However, carbon storage varies considerably between Indian mangrove ecosystems.
India's mangrove forests cover approximately 4,992 square kilometres. They occur mainly along the east coast in West Bengal, Odisha, Andhra Pradesh and Tamil Nadu; along the west coast in Gujarat, Maharashtra, Goa, Karnataka and Kerala; and across the Andaman and Nicobar Islands.
The Sundarbans contain India's largest continuous mangrove tract, with extensive tidal creeks, high sediment flux and rich biodiversity. Bhitarkanika in Odisha is the country's second largest mangrove system and has high biomass accumulation associated with nutrient-rich estuarine conditions.
The Godavari Krishna delta mangroves are influenced by river discharge, while Pichavaram and the Vellar estuaries have lagoonal systems with restricted tidal exchange. The Gulf of Kachchh has an arid environment, limited freshwater availability and high salinity, resulting in shorter mangrove vegetation. These differences in environmental conditions influence forest structure, species composition, disturbance and, ultimately, biomass and carbon storage.
The study finds considerable differences in above-ground biomass across India's mangrove ecosystems.
In mature stands of the Sundarbans, above-ground biomass is estimated at between 150 and more than 250 Mg ha⁻¹, reflecting species richness and favourable sedimentation. In Bhitarkanika, values exceed 200 Mg ha⁻¹, associated with relatively undisturbed stands and nutrient-rich estuarine conditions.
The picture is different in the Gulf of Kachchh and parts of Maharashtra, where above-ground biomass ranges from approximately 30 to 85 Mg ha⁻¹. High salinity, limited freshwater input and stunted tree growth contribute to the lower values.
In Tamil Nadu, mangroves such as those at Pichavaram have above-ground biomass ranging from approximately 60 to 120 Mg ha⁻¹. Restricted tidal exchange and periodic freshwater inflows influence these systems.
These variations demonstrate why carbon estimates cannot simply be transferred from one mangrove landscape to another.
What happens beneath the surface is equally important. Mangrove roots form extensive systems that help plants survive in challenging intertidal environments. They anchor sediments, facilitate aeration and help plants obtain nutrients despite regular flooding.
This below ground biomass in Indian mangroves ranges from approximately 30 to 200 Mg ha⁻¹. Higher values are observed in species with elaborate prop root or pneumatophore systems.
Root turnover also plays an important role in carbon cycling. Fine roots are continually produced and replaced, contributing organic matter to sediments. This process adds to sediment organic carbon and reflects the high productivity and adaptation of mangroves to flooded conditions.
The balance between above- and below-ground biomass also varies between ecosystems. In hypersaline areas such as Gujarat, below ground biomass forms a greater proportion of total biomass. In estuarine systems, below ground biomass remains substantial but is more closely proportional to above ground growth.
Several interacting factors determine biomass accumulation.
Indian mangroves include species such as Avicennia marina, Avicennia officinalis, Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza, Ceriops tagal, Ceriops decandra, Heritiera fomes and Sonneratia apetala.
These species differ in growth form, rooting structure, wood density and physiological adaptations, all of which influence biomass accumulation.
Avicennia marina, the most widely distributed species, is found extensively in hypersaline regions. It has lower wood density than Rhizophora and Bruguiera, resulting in moderate biomass despite high stem density.
Rhizophora mucronata and Rhizophora apiculata develop taller and more robust stems as well as prop roots, contributing to both above and below ground biomass. Bruguiera gymnorrhiza grows in deeper soils and estuarine conditions and contributes substantially to biomass and soil carbon.
Ceriops decandra often forms dense, shorter stands with relatively high root biomass compared with stem biomass.
The distribution of these species therefore helps determine carbon storage patterns across India's mangrove ecosystems.
Sediment availability is another important determinant. Deltaic systems often have higher biomass because nutrient-rich fine sediments support rapid root and stem growth. The amount and characteristics of sediment entering and remaining within a mangrove system therefore influence its ability to accumulate biomass.
Tidal range affects oxygen availability, flushing intensity and soil chemistry. These conditions influence which species can establish and how quickly they grow, ultimately affecting biomass accumulation.
Salinity has a particularly strong influence on mangrove structure. Hypersaline conditions suppress stem growth but can increase the allocation of biomass to roots. Above ground biomass generally declines as salinity increases, while below ground biomass can increase under low- to moderate-salinity conditions as plants allocate more carbon to their root systems. Freshwater availability therefore matters not only to the wider health of coastal ecosystems but also to how mangroves grow and distribute their biomass.
Freshwater inflows, seasonal monsoon patterns and cyclone disturbances influence biomass accumulation. Human activities can have equally significant effects. Aquaculture expansion, embankment construction, dredging and pollution can reduce stand density and productivity, directly affecting biomass and carbon storage.
The study finds substantial spatial variation across the Sundarbans, Bhitarkanika, Kerala, Odisha, Maharashtra, Tamil Nadu, the Andaman Islands and managed plantations. Differences in salinity, geomorphology, forest age, species composition and levels of disturbance mean that mangrove systems can accumulate and retain carbon in very different ways. This makes the use of a single representative biomass or carbon value problematic for national blue carbon accounting.
The Sundarbans itself demonstrates this variation. Inner, middle and outer island zones show declining above- and below-ground biomass from the inner to outer zones. Increasing salinity stress, reduced freshwater input and greater exposure to tidal energy contribute to this pattern. Bhitarkanika represents one of the highest biomass and carbon storage hotspots in mainland India.
In core zones, above-ground biomass can reach approximately 1,100 to 1,150 Mg ha⁻¹, while below-ground biomass can reach around 900 Mg ha⁻¹. These values are substantially higher than those reported for the Sundarbans and west coast mangroves and are associated with long-term protection, limited anthropogenic disturbance and favourable hydro-sedimentary conditions.
West coast mangroves in Kerala, Tamil Nadu and Maharashtra show moderate biomass and carbon stocks, with notable differences between conserved and disturbed systems. Evidence from Bichitrapur in Odisha further illustrates the importance of forest age. Young planted stands of approximately 20 years old store around 165 Mg ha⁻¹ of total biomass and approximately 115 Mg C ha⁻¹ of ecosystem carbon. Natural stands more than 50 years old accumulate nearly four times as much biomass and almost three times as much ecosystem carbon.
This suggests that mangrove afforestation can contribute to carbon sequestration, but young plantations cannot rapidly replicate the carbon stocks of mature natural forests. The conservation of existing mature mangroves therefore remains important. The Andaman Islands are another major carbon hotspot, with high above and below ground biomass associated with minimal disturbance, high species diversity and favourable climatic and geomorphic conditions.
India recognises mangrove biomass carbon as an important component of nature-based climate solutions and coastal climate resilience. National initiatives such as the Green India Mission and the National Coastal Mission include mangrove protection, restoration and biomass enhancement as pathways for climate mitigation and ecosystem recovery.
Reliable estimates of mangrove biomass carbon are consequently important for evaluating restoration outcomes and reporting carbon sequestration contributions towards India's Nationally Determined Contributions under the Paris Agreement. However, conventional blue carbon assessments often aggregate carbon stocks without adequately capturing differences between species, climatic conditions and levels of human influence.
The study finds that different mangrove biomass carbon pools vary in their stability, permanence and relevance for climate mitigation and carbon credit integrity. Above ground biomass is particularly vulnerable to disturbance, while below ground biomass can provide a more stable carbon reservoir through extensive root systems. Soil-associated carbon, influenced by root turnover and sediment interactions, is identified as the most durable and verifiable carbon pool.
The study therefore highlights the need for depth-inclusive biomass accounting to support robust mangrove-based carbon markets and evidence-based blue carbon policies. Incorporating depth-resolved biomass frameworks into national monitoring, reporting and verification systems could improve the transparency and credibility of India's mangrove-based climate mitigation strategies.
The study identifies several priorities for improving biomass carbon research in India. These include establishing coordinated, long-term biomass monitoring networks across India's mangrove regions and incorporating salinity into assessments to strengthen comparisons between sites and improve carbon allocation modelling.
The researchers also call for greater use of technologies such as LiDAR, hyperspectral imagery and structure from motion photogrammetry to improve biomass mapping at landscape scales. Eco physiological research examining how salinity, inundation and nutrient gradients influence biomass allocation can provide a better understanding of regional carbon dynamics. Greater collaboration between ecologists, foresters, hydrologists and remote sensing specialists is also needed to strengthen biomass research and India's contribution to global blue carbon initiatives.
Mangroves sit at a critical intersection of land and water. Their ability to withstand salinity, flooding and changing tidal conditions allows them to support coastal ecosystems and communities while storing substantial quantities of carbon.
But India's mangroves do not function as a single, uniform ecosystem. A mangrove forest in a nutrient-rich delta behaves differently from one growing under hypersaline conditions. A mature natural forest stores carbon differently from a young plantation. Freshwater availability, sediment movement, tidal exchange and human disturbance can all change the amount and location of carbon stored within these ecosystems.
This variation matters as India expands its use of nature-based approaches to climate mitigation and considers the role of blue carbon in climate policy. Better carbon accounting is therefore not simply a matter of producing a more precise national number. It requires understanding the ecological and hydrological conditions that allow different mangrove forests to accumulate, retain and transfer carbon.
For India's coastal communities, protecting those conditions also means protecting ecosystems that support fisheries, livelihoods, groundwater and safety from coastal hazards. The evidence points to a clear research priority: India's mangrove carbon cannot be understood through one number. It needs to be measured in the places where forests meet tides, freshwater, sediments and people.