Blue Carbon: A Complete Guide To Coastal Carbon Ecosystems

It is well known that forests help fight climate change, but ocean and coastal ecosystems are also highly effective carbon sinks. Blue carbon refers to the carbon that is captured and stored by coastal ecosystems, such as mangroves, seagrass meadows, and salt marshes.

Although they cover less area than forests, blue carbon ecosystems are more efficient at locking away carbon. Pound for pound, blue carbon ecosystems can absorb carbon up to 10 times faster than forests. Much of this carbon is in their soils, where it decomposes slowly, allowing blue carbon ecosystems to store twice as much carbon per equivalent area.

Blue carbon ecosystems not only prevent climate change, but they also protect coastal communities from its harmful impacts, such as rising seas and flooding. They also provide important habitats for birds, marine life, and land animals, and support diverse, interconnected food webs.

Yet even as blue carbon ecosystems gain attention for their role in climate mitigation and adaptation, they’re being destroyed at an alarming rate. It is estimated that every minute, up to three football fields of coastal habitats are being lost.

Read on to learn more about the different blue carbon ecosystems, how they lock away carbon, the benefits they provide for communities and wildlife, what’s putting them at risk, and how you can support their conservation.

Types of Blue Carbon Ecosystems

Three main types of ecosystems account for the vast majority of blue carbon storage: mangroves, seagrass, and salt marshes. In the sections below, we’ll look at what makes each of these habitats unique and where they’re typically found.

Mangroves

What Are Mangroves?

Mangroves are salt-tolerant trees or shrubs that grow in the intertidal zone of tropical and subtropical coasts where land meets the sea. They’re easily recognized by their sprawling, tangled roots, which rise above the ground and water. Scientists currently recognize 82 mangrove species and their hybrids, though efforts are ongoing to refine this classification and reach a consensus on a definitive list.

Mangrove Adaptations

Mangroves are hardy plants that thrive in harsh coastal environments where they’re regularly flooded during high tide. They rely on several unique adaptations to survive these conditions, which help them stay rooted in waterlogged soil, withstand waves, and cope with high salt and low oxygen levels:

• Sturdy Roots: Mangroves’ stilt-like roots anchor them in soft, shifting soil, keeping them stable even when submerged under water.
• Breathing Roots: Their above-ground roots help them “breathe” in oxygen-poor soils.
• Salt-Filtration: While saltwater would kill most other trees, mangroves are specially adapted to filter it out. Some species can block up to 90% of the salt at the root level, while others excrete it through special glands on their leaves.
• Floating Seedlings: Unlike most plants, mangrove seeds start to sprout while still attached to the parent tree. The young seedlings eventually fall off, float in the water, and take root in a new spot.

Where Mangroves Grow

Mangroves cover more than 56,000 square miles (147,000 square kilometers) of the earth’s surface – an area roughly the size of Nepal. Southeast Asia holds one-third of this total, while Indonesia alone accounts for 21% of the world’s mangroves. The largest mangrove forest in the world is the Sundarbans, which spans over 3,700 square miles (9,600 square km) across southern Bangladesh and eastern India.

Mangroves can’t survive freezing temperatures and are typically found in warmer climates. Today, they naturally grow as far north as Bermuda (32.36°N) and as far south as Victoria, Australia (38.90°S). As global temperatures rise, their range is expanding into areas that were once too cold. In the United States, for example, mangroves were previously found only as far north as Florida. In 2024, they were documented in southern Georgia, growing 50 miles (80 kilometers) beyond their former range.

Mangrove Loss

However, even as mangroves expand into higher latitudes, their overall global coverage continues to decline. An estimated 20–35% of the world’s mangrove forests were lost between 1980 and 2010. While the rate of loss has slowed in recent decades, it hasn’t stopped. Over the past two decades, approximately 1.67 million acres (677,000 hectares) of mangroves were lost. Although some of this was offset by the establishment of new mangrove areas, there was still a net global decline of 702,000 acres (284,000 hectares) during that period.

Today, half of the remaining global mangrove area is at risk of collapse. One in five mangrove ecosystems is classified as Endangered or Critically Endangered by the IUCN, indicating a severe risk.

Seagrass

What is Seagrass and How is It Different from Seaweed?

Seagrass is a type of aquatic flowering plant that grows fully submerged in shallow coastal waters. Despite its name, seagrass isn’t actually a grass, and it’s not seaweed either.

While seaweed is a type of algae, seagrass is a true flowering plant that has roots, leaves, flowers, and seeds, just like plants on land. Its closest relatives are lilies and orchids. Seagrass absorbs nutrients from the seafloor through its roots, while algae like seaweed lack roots and instead take in nutrients directly from the surrounding water through their entire surface.

Though not true grasses, seagrass gets its name from its green grass-like leaves. There are 72 known species of seagrass, which vary in shape and size. They are commonly known by names like eelgrass, turtle grass, shoal grass, and manatee grass, which can vary by region. While some seagrass leaves look like flat blades of grass, others are shaped like ovals, fern fronds, or even long spaghetti noodles.

Where Seagrass Beds Are Found

Seagrass is found along coastlines worldwide, except in Antarctica. Like all plants, seagrass needs sunlight to perform photosynthesis. Because of this, seagrass is only able to grow in clear, shallow waters. In some places, seagrass grows densely clumped together and carpets large areas of the seafloor. These ecosystems are known as seagrass beds or meadows.

Salt Marshes

Salt marshes are coastal wetlands that are regularly flooded with salty seawater that is brought in by the tides. Salt-tolerant plants, such as grasses, sedges, and reeds, sprout up from the soggy ground, painting the landscape with shades of gray, brown, and green. Their deep, mucky soils are made up of mud and peat, the latter of which is a spongy material consisting of decomposing plant matter.

Though salt marshes are found worldwide, they are most common in temperate climates and higher latitudes. In tropical regions, salt marshes are usually replaced by mangroves.

Carbon Storage and Climate Mitigation

As their name implies, blue carbon ecosystems capture carbon dioxide and store it in their leaves, branches, roots, and soils. By removing carbon from the atmosphere, blue carbon ecosystems play an important role in mitigating the global climate crisis.

Though blue carbon ecosystems cover far less land area than terrestrial forests, they are carbon-sequestering powerhouses. Mangroves for instance can store up to 10 times more carbon per acre than land-based forests.

This is because terrestrial forests store most of their carbon in their biomass (branches, roots, and leaves), while blue carbon ecosystems store most of their carbon in their soils. In fact seagrass meadows and salt marshes often store more than 95% of their carbon in their soils.

Wet coastal soils have much lower oxygen levels than those on the forest floor, which causes dead plant matter to take a longer time to decay. As a result, the carbon stored in coastal soils can remain trapped there for thousands of years.

 

This chart compares the amount of carbon stored in the soils and biomass of terrestrial forests with that of blue carbon ecosystems, including mangrove forests, seagrass meadows, and salt marshes. Data sources: Pendleton et al. 2012 and Pan et al. 2011

Co-Benefits and Ecosystem Services Beyond Carbon

In addition to mitigating climate change, blue carbon ecosystems nurture both land and marine biodiversity and support human well-being. Below are a few additional reasons why blue carbon ecosystems are important.

Habitats and Food for Animals

Mangroves, seagrass, and salt marshes provide critical habitats for a wide range of marine and coastal wildlife.

The dense, intertwining roots of mangroves act as sheltered breeding and nursery grounds, protecting fish and shrimp species from larger predators. The shrubby trees are also home to oysters, barnacles, sponges, and anemones, which cling onto the submerged roots. Pelicans build their nests at the top of mangrove trees, while lobsters burrow down in the deep, muddy soil.

Many small animals can also be found hiding among swaying seagrass beds and thick marsh grasses. Next time you’re diving or snorkeling, keep an eye out for skinny pipefish and tiny seahorses that use their camouflage to blend in with seagrass blades.

Along with providing a safe haven, blue carbon ecosystems are an important source of food for animals both above and below the sea. Animals like dugongs, manatees, and sea turtles can be found grazing on seagrass leaves. There’s a reason that dugongs are nicknamed “sea cows” – an adult dugong can eat up to 88 pounds of seagrass in a day. That’s about the weight of 50 heads of lettuce.

 

The average adult green sea turtle consumes about 4.5 pounds of seagrass leaves in a day.

Birds like herons, egrets, and geese are frequent visitors to salt marshes as they come to forage for insects, crabs, and fishes. Raccoons and mink can also be spotted visiting the wetlands in search of a bite to eat.

Even the dead and decomposing biomass of blue carbon ecosystems serves an important ecological role. Crabs feast on the decaying leaves that fall from mangroves. As seagrass breaks down, the organic matter provides nutrients for organisms like worms, sea cucumbers, and various filter feeders.

Coastal Protection and Erosion Control

As climate change causes tropical storms to become more powerful and sea levels to rise, there is greater risk of coastal flooding and destruction. The vegetation that fringes shorelines acts as natural barriers, defending communities against these damaging impacts.

Mangrove roots stand strong against crashing waves and storm surges, which is when seawater is pushed ashore during a big tropical storm. A 100 meter stretch of mangroves can reduce the height of waves by up to 66%. It is estimated that mangroves protect 15 million people from flooding every year and reduce property damage by more than $65 billion. These numbers will only grow as climate impacts get worse.

Though they’re not as burly as mangroves, salt marsh grasses and plants are highly effective at reducing the power of smaller waves. Their peat soils also help prevent flooding by absorbing water like a giant sponge.

Mangrove roots, seagrass, and marsh plants also help to hold sediment in place and stabilize shorelines, thus preventing beach erosion. Blue carbon ecosystems don’t only safeguard communities on land. By trapping sediments and filtering out pollutants before they reach the ocean, blue carbon ecosystems also protect coral reefs and life under water.

 

Livelihoods and Economic Benefits

Currently, more than 600 million people live near the world’s coasts. These coastal communities depend heavily on their marine environments for both income and food security. Many coastal inhabitants make their living from fishing and rely on seafood as a cheap source of protein. In the Maldives, for instance, the local population relies on seafood for more than three-quarters of their protein.

Healthy blue carbon ecosystems play a critical part in maintaining the fish stocks that sustain these populations. The commercial fisheries that feed the world also rely on the productivity of these coastal ecosystems.

Many of the fish that we eat spend their early days swimming among mangrove roots and seagrass leaves. Nearly all (95%) commercial fish species depend on coastal habitats at some point during their life. If these ecosystems are destroyed, fish won’t have a safe place to raise their young and their populations will decline.

Recreation and Tourism

Blue carbon ecosystems are also a great place to visit and explore. They support tourism jobs and provide recreational opportunities, such as birdwatching, kayaking, boat tours, and fishing. Because they support coral reefs and the entire marine food web, blue carbon ecosystems also ensure we have rewarding diving, snorkeling, and whale-watching experiences.

Threats to Blue Carbon Ecosystems

Despite the numerous benefits that blue carbon ecosystems bring to people, nature, and the economy, they are among the most threatened ecosystems. Our world’s blue carbon ecosystems are rapidly shrinking in size, as 98,000 to 2.4 million acres are destroyed each year. It is estimated that half of the world’s seagrass has been lost since the 1990s. Though salt marshes have fared slightly better, they’ve still lost a quarter of their coverage since the 1800s.

The destruction of these vital coastal habitats is largely the result of development, agriculture, aquaculture, pollution, and overharvesting of resources. As the world’s population grows, the pressure on these ecosystems continues to increase.

• Coastal Development and Disturbances: Mangroves, seagrass, and wetlands are often removed to construct resorts, golf courses, and other shoreline infrastructure. In the Caribbean, it is common for hotels to clear mangroves or seagrass to create “pristine” beaches and swimming areas for tourists. Boat anchors and propellers also pose a danger to delicate seagrass beds.
• Resource Extraction: Mangroves are a cheap source of fuel and durable building material, and are often cut down for their timber.
• Climate Change Impacts: Rising sea levels, stronger tropical storms, and warming ocean temperatures all threaten blue carbon ecosystems. Salt marshes can drown if sea levels rise too quickly, while heat stress and extreme weather events can damage mangroves and seagrass beds.
• Food Production: Coastal ecosystems are frequently cleared to make way for croplands, such as rice paddies and oil palm plantations, as well as aquaculture ponds, particularly shrimp farms.
• Water Pollution: Nutrient-rich runoff from agriculture, untreated sewage from coastal resorts, and discharges from boats all contribute to the formation of harmful algae blooms. These blooms—like the massive sargassum invasions seen in Mexico and the Caribbean—can smother seagrass beds. In high-use swimming areas, chemicals from sunscreen can accumulate, further stressing seagrass.

When mangroves, seagrass, or salt marshes are degraded or destroyed, their enormous carbon stores are released into the atmosphere. Studies show that the degradation and conversion of coastal ecosystems releases up to 1.02 billion metric tons of carbon dioxide into the atmosphere each year. That’s the same amount of carbon that is emitted by driving 2.5 trillion miles, or 101 million laps around the earth.

In addition to releasing carbon, this loss of coastal vegetation leaves coastal destinations and communities unguarded against the powerful waves that strike against their shores.

Conservation and Restoration of Blue Carbon Ecosystems

To safeguard the climate and biodiversity benefits that blue carbon ecosystems provide, we must halt their loss and support their recovery. Below are strategies that communities, governments, businesses, and travelers can implement to conserve and restore mangroves, seagrass, and salt marshes.

• Low-Impact Development: Coastal development should be designed to minimize disruptions to blue carbon ecosystems. This includes implementing zoning laws, setting coastal buffer zones, and designing resorts and infrastructure that coexist with mangroves, wetlands, and seagrass beds.
• Minimizing Pollution: Improving wastewater treatment, reducing agricultural runoff, and promoting eco-friendly boating practices help protect fragile coastal ecosystems. Using reef-safe sunscreen in swimming areas also reduces chemical stress on seagrass.
• Ecotourism and Immersive Education: Guided tours, kayaking excursions, and interpretive signage can raise awareness among travelers and locals alike about the value of mangroves, seagrass, and salt marshes. Experiencing the benefits of these ecosystems firsthand, such as watching turtles feed on seagrass or paddling through a mangrove tunnel, can shift perceptions and strengthen support for conservation.
• Sustainable Tourism Practices: When visiting coastal destinations, be sure to engage in sustainable tourism to prevent physical damage to the plants. For instance, avoid touching, standing, or anchoring on seagrass. Encouraging the use of reef-safe sunscreen in swimming areas also limits chemical stress on seagrass. Choose companies that adhere to low-impact practices.
• Community-Based Conservation: Engaging communities in ecosystem protection ensures that conservation efforts are equitable, locally supported, and long-lasting. This could include training on sustainable resource management, developing alternative livelihood opportunities, strengthening land rights, direct payments for conservation, and roles such as monitoring or patrolling.
• Legal Protection: Establishing legally protected areas can help prevent harmful activities in vulnerable zones. However, regulations must be backed by strong enforcement and public awareness to ensure protection goes beyond a paper designation.
• Restoration Projects: When ecosystems are damaged, restoration such as replanting mangroves or transplanting seagrass can help recover carbon stocks and ecosystem services. Successful projects often pair science with local knowledge and community involvement.

Scaling and Funding Blue Carbon Projects

Blue Carbon Credits and Offsets

You can help fund the conservation and restoration of blue carbon ecosystems by purchasing carbon offsets, also known as carbon credits. These blue carbon credits fund projects that reduce emissions by either protecting existing blue carbon ecosystems or restoring degraded ones. Most are community-based, creating benefits for local people and offering a financial incentive for communities to take part in long-term conservation. Unlike many mangrove restoration projects, carbon credits are independently verified to ensure that emissions reductions are real and measurable, offering greater accountability and confidence in their impact. To better understand how this works, check out our blog post on how carbon offsets work.

Every blue carbon offset project takes a unique approach, tailored to the local situation. For instance, the Mikoko Pamoja project is protecting 290 acres (117 hectares) of mangroves on Kenya’s southern coast and restoring degraded beach areas by planting thousands of mangrove seedlings. The project engages local villagers through education, replanting efforts, and forest monitoring. In addition to conserving coastal ecosystems, the project reinvests its funding in local healthcare, skills training, and education. By preserving these valuable blue carbon ecosystems and creating livelihood opportunities, the project fosters marine health and strengthens the resilience of Kenya’s coastal communities.

When you offset your carbon with Sustainable Travel International, your contribution supports projects like Mikoko Pamoja, as part of a diverse portfolio that includes blue and teal carbon, forestry, energy, and innovative climate tech solutions.

 To get started, use our carbon footprint calculator to estimate the emissions generated by your travel and purchase carbon offsets equivalent to your footprint. We also offer solutions for tour operators, hotels, and other businesses seeking to implement their own carbon offset programs.