What is a blue carbon ecosystem and why are they important?
Blue carbon refers to the carbon found in coastal and marine ecosystems such as seagrass meadows, mangroves, and salt marshes [1]. Although these ecosystems are concentrated in tropical regions, at least one type of these coastal ecosystems are found in almost every country with a coastline [3].
From a climate mitigation perspective, blue carbon ecosystems are integral and have been described as a natural climate solution [2]. Despite covering approximately only 0.5% of the sea floor, these carbon sinks contribute to more than 50% of global carbon sequestration in the oceans, with the oceans overall absorbing around 25% of carbon released into the atmosphere [2, 4].
Additionally, these coastal habitats provide benefits and ecosystem services in the form of nursery habitats for birds, fish and other animals thereby contributing to the creation of diverse ecological communities [3]. Over 3 billion humans also rely on these ecosystems for their food security, and their sources of livelihood and protection from the effects of extreme weather events such as storms, floods and coastal erosion [5, 2]. As climate-induced weather events become more common, this protective role will become even more important in enabling communities to adapt.
The threats to blue carbon ecosystems and protection
Blue carbon ecosystems are among the most threatened environments globally with rates of habitat loss comparable to or even greater than tropical forests. 67% of mangroves are already lost or degraded [3, 5]. Habitat degradation is generally due to habitat conversion such as for urban infrastructure and agricultural land. This is problematic because disturbance causes the stored carbon to be released back into the atmosphere as carbon dioxide, thereby contributing to climate change [3]. In a self-perpetuating cycle, the effects of climate change then further impact these ecosystems such as through sea level rise and ocean acidification [2]. Other issues that affect these ecosystems include pollution, overexploitation for fishing and activities further inland such as agricultural runoff [4].
If we are to truly benefit from the carbon sequestration and climate adaptation benefits of blue carbon ecosystems, this destruction needs to stop. We need to refocus our efforts towards their conservation and restoration. It has been estimated that protecting blue carbon ecosystems could prevent emissions of 304 terra gram (Tg) [1] [2] of carbon dioxide per year, and restoration could sequester an extra 841 Tg. This amounts to approximately 3% of annual global GHG emissions [2].
To increase the recognition of the importance of blue carbon ecosystems, countries should incorporate these ecosystems in their regulatory frameworks and policies [4]. For example, as of 2023, only 61 countries out of the 151 countries with at least one of these coastal habitats have included the conservation and restoration of coastal habitats in their NDCs (Nationally Determined Contributions) [6, 7]. Linked to this, mobilising finance remains a key issue and will require innovative public and private funding mechanisms to ensure that healthy blue carbon ecosystems can continue to provide their multiple environmental, economic and social benefits [5].
Conclusion
Notwithstanding the multiple and intersecting challenges, change is possible. The submission of updated NDCs in early 2025 provides one mechanism through which countries can begin to take more concerted action to protect blue carbon ecosystems. If no urgent action is taken, the degradation and loss of these ecosystems will persist and their multifaceted benefits to people, planet and wildlife will be compromised.
