Blue carbon refers to the carbon captured and stored by the world’s ocean and coastal ecosystems. These ecosystems reduce atmospheric carbon dioxide, a greenhouse gas. While terrestrial forests are recognized for carbon absorption, coastal and marine environments also contribute to carbon sequestration.
Key Blue Carbon Ecosystems
The primary ecosystems responsible for blue carbon storage are mangroves, salt marshes, and seagrass meadows. These vegetated coastal habitats are found along coastlines on every continent except Antarctica. Despite their relatively small footprint, these ecosystems are highly productive and effective at storing carbon.
Mangroves are salt-tolerant trees and shrubs thriving in tropical and subtropical coastal areas. Their dense root systems and ability to grow in waterlogged, oxygen-poor soils allow them to efficiently trap and bury organic matter.
Salt marshes are coastal wetlands dominated by salt-tolerant grasses and herbs, found in temperate regions. These marshes accumulate mineral sediment and organic material, building deep, carbon-rich soils.
Seagrass meadows consist of submerged flowering plants with extensive root systems that grow in shallow coastal waters. These underwater meadows contribute significantly to carbon storage, with most carbon stored in their soils.
The Process of Carbon Sequestration
Blue carbon ecosystems capture and store carbon through biological and geological processes. Plants in these ecosystems, such as mangroves, salt marsh grasses, and seagrasses, absorb carbon dioxide from the atmosphere during photosynthesis. This carbon is converted into organic compounds and stored in the plant’s biomass, including leaves, stems, and extensive root systems.
When plant material dies, it accumulates in the waterlogged soils and sediments beneath these ecosystems. The anaerobic, or oxygen-deprived, conditions in these environments significantly slow decomposition. This lack of oxygen prevents microbes from breaking down organic matter quickly, allowing carbon to remain locked away for hundreds or even thousands of years. The carbon-rich soils in these habitats can be several meters deep, sequestering large quantities of carbon below ground.
The Global Importance of Blue Carbon
Blue carbon ecosystems are important in the global carbon cycle by removing and storing atmospheric carbon dioxide. These coastal systems are efficient carbon sinks, absorbing more carbon than they release. They sequester carbon at rates significantly higher than terrestrial forests, storing two to four times more carbon per area than tropical forests.
Despite covering less than 1% of the ocean floor, blue carbon ecosystems may account for over 50% of all carbon buried in marine sediments. Seagrasses, for instance, occupy less than 0.2% of the world’s oceans and are estimated to sequester approximately 10% of the carbon buried in ocean sediment annually. This capacity to store large amounts of carbon helps mitigate climate change by reducing atmospheric carbon dioxide.
Protecting Blue Carbon Habitats
Blue carbon ecosystems face threats that can compromise their ability to store carbon and lead to the release of previously sequestered carbon back into the atmosphere. Coastal development, including urbanization and infrastructure expansion, is a significant cause of habitat loss. Pollution from agricultural runoff, industrial waste, and plastics degrades these environments, affecting plant growth and carbon sequestration potential.
Climate change impacts, such as rising sea levels and ocean acidification, pose additional challenges. Sea level rise can inundate salt marshes, potentially leading to their loss, while ocean acidification can weaken mangrove root systems. Conservation and restoration efforts are underway to protect these habitats. Strategies include establishing marine protected areas, implementing sustainable coastal management plans, and restoring degraded ecosystems to enhance their carbon sequestration capacity.