Updated: Sep 22
Coastal and marine ecosystems including mangroves, seagrass beds and tidal marshes take up and store vast quantities of carbon. This process is termed ‘blue carbon’, to distinguish it from terrestrial carbon sinks such as forests and peat bogs. As the negative effects of carbon emissions on climate change have become increasingly studied, so have the biological systems sequestering and releasing carbon. Given the important role blue carbon ecosystems play in mitigating climate change, as well as their biodiversity, and economic value, now, and increasingly as we head into the future, they need to be cared for, conserved and replenished.
As well as storing carbon, these coastal ecosystems are some of the most productive on Earth, providing nurseries for juvenile fish, and economic benefits for fisheries. They also provide protection from storms to coastal communities and land through wave attenuation and sediment aggregation by roots and seagrasses. For example, mangroves globally have an estimated yearly value of around $1.6 billion each year in ecosystem services, which support a huge number of communities worldwide.
Between them, mangroves, seagrass meadows and salt marshes cover almost 200,000 square miles around the world, reaching every continent apart from Antarctica.
Mangroves, salt marshes, and seagrass meadows are all formed by plants, which absorb carbon from the air to photosynthesise. This carbon is stored as new growth in the leaves, stems and roots. The roots also bind the sediment together and slow the carbon from cycling back into the atmosphere. In fact, 95% of the carbon stored in seagrass beds is actually bound in the sediment.
Blue carbon makes up a huge part of the earth's carbon cycle, more so in fact that terrestrial forests per unit area. 83% of global carbon is circulated through the oceans, and half of the sequestered carbon in the oceans is held in the sediments of coastal systems, despite these ecosystems making up only 2% of the total ocean area worldwide. In a very similar way to forests, these blue carbon ecosystems when healthy, sequester carbon, but when degraded emit huge amounts of carbon into the atmosphere and contribute to climate change, whilst simultaneously having a reduced potential to store carbon.
The alarming news is that blue carbon storing ecosystems are being lost at a huge rate. Around 30% of the world's seagrass meadows have been lost over the last hundred years, while approximately 50% of the world's mangrove forests have been lost to clearance for beachfront housing, and crustacean farms. The world’s salt marshes are in the largest state of decline, with over half having been destroyed. And we haven’t stopped yet! Mangroves continue to be lost at a rate of 2% per year, accounting for around 10% of the carbon emissions resulting from deforestation as a whole.
It’s been estimated that around a billion tons of carbon dioxide are released into the atmosphere each year from degraded coastal ecosystems, equivalent to 20% of the emissions resulting from deforestation globally.
Although these coastal ecosystems are degraded, and continue to be damaged, there is a glimmer of hope. An increasing number of groups, organisations and policies are being put in place to protect, conserve and replenish these vital blue carbon sinks. These groups educate on the importance of the mangroves, salt marshes and seagrass meadows, and help ensure that environmental policy protects them from clearance damage and alteration.
Furthermore, some organisations actively plant mangroves and seagrass beds to regrow them in their historic ranges. For example, The Mangrove Action Project, a US-based nonprofit which collaborates with stakeholders at all levels to preserve, conserve, and restore our world’s mangrove forests. They have actively rehabilitated mangroves in Thailand and Indonesia, as part of post-tsunami recovery, while being involved in consulting on shoreline and mangrove restoration projects elsewhere including running training workshops in Cambodia, El Salvador, French Guiana, Honduras, India, Indonesia, Malaysia Myanmar, Senegal, Sri Lanka, Tanzania, and Thailand.