The Blue Carbon Mapping Project

Charities urge stronger protection for UK seas as landmark reports reveal amount of carbon stored in seabed habitats for the first time  

• New series of reports – The Blue Carbon Mapping Project – provide the first estimate of carbon stored in UK seabed habitats, including in Marine Protected Areas (MPAs). 
• 244 million tonnes of organic carbon* are stored in just the top 10cm of the UK’s seabed sediments – principally made of mud – plus vegetated habitats including saltmarshes and seagrass beds. 43% of this carbon is stored in MPAs. 
• Seabed disturbances, including from bottom trawling and offshore development, are identified as threats to blue carbon stores, as nature charities call for stronger protections for UK seas. 

A new series of reports published today by a coalition of nature charities means the UK is the first nation to map and estimate the amount of carbon stored in its seabed habitats, including in Marine Protected Areas (MPAs). 

The Blue Carbon Mapping Project, completed by the Scottish Association for Marine Science (SAMS) on behalf of WWF, The Wildlife Trusts and the RSPB, reveals that 244 million tonnes of organic carbon are stored in just the top 10cm of UK seabed habitats, with 98% stored in seabed sediments such as mud and silt. 

UK seabed habitats could capture up to 13 million tonnes of organic carbon every year – almost three times the amount sequestered by the UK’s forests – 4.8 million tonnes [1] – although forests cover a much smaller area (32,500 km2). 

Seas around the UK and Isle of Man cover nearly 885,000 square kilometres – over three times the size of the UK’s land mass. This vast area is host to habitats that capture and store carbon, known as ‘blue carbon’. They include seabed sediments (made of mud, silt and sand), vegetated habitats (seagrass meadows, saltmarshes, kelp forests and intertidal seaweeds), maerl beds and biogenic reefs, such as mussel beds and honeycomb worm reefs. 

Carbon is primarily absorbed by phytoplankton, which drift to the bottom of the sea when they die and are added to seabed sediment. The research analysed the storage capacity of just the top 10cm of sediment. Some sediments are hundreds of metres thick and contain millennia’s worth of carbon, so the total carbon stored will be far greater. 

The Blue Carbon Mapping Project highlights how physical disturbances to the seabed, including from human activity such as bottom trawling, as well as moorings and offshore developments, pose threats to blue carbon stores. Disturbing seabed habitats can release large amounts of carbon into the atmosphere, worsening climate change. 

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In Sussex, our key areas of work in relation to Blue Carbon are:

Saltmarsh at Rye Harbour Nature Reserve: Sussex Wildlife Trust is working to protect 26 ha of saltmarsh habitat at our nature reserve at Rye Harbour. Saltmarsh is part of a mosaic of habitats at this site, supporting a huge amount of biodiversity and naturally storing carbon. 

Wider marine policy: Sussex Wildlife Trust continually champions for better protection of our blue carbon habitats through advocating for protection for our marine environment. Through our marine policy work, we fight for nature to be put first when it comes to marine protected areas, fisheries, and development at sea.

Sussex Kelp Recovery Project: In Sussex, the work of the Sussex Kelp Recovery Project partners saw 300km2 of seabed protected from bottom trawling. This vital protection will reduce seabed disturbance and protect potential blue carbon stores in the seabed locally.

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WWF, The Wildlife Trusts, and the RSPB are calling on governments across the UK to strengthen protections for valuable blue carbon stores – including in MPAs – by minimising the impacts of human activities on the seabed. Most MPAs were not designated to protect blue carbon, and failing to protect these areas from disturbance could threaten climate and biodiversity goals – including net-zero and protecting 30% of seas by 2030. 

WWF, The Wildlife Trusts & the RSPB call for: 

Better management of MPAs 

• Ensure that all MPAs are protected from destructive activities that damage blue carbon habitats and threaten marine life. 
• Account for both carbon and biodiversity in designating new protected areas, to support ecosystem resilience and the role seas play in climate mitigation. 

Improved strategic planning of activities in UK seas 

• Consider blue carbon in UK marine plans, avoiding damaging activities in MPAs and other key areas for blue carbon and wildlife that are not protected. 
• Minimise the impacts of fishing and developments by undertaking blue carbon impact assessments. 
• Support a just transition for fishing industries away from activities that damage the seabed. 

More investment and research on protecting blue carbon 

• Allocate funding to restore habitats including seagrass beds and saltmarshes. 
• Support research and monitoring of blue carbon dynamics. 
• Add seagrass and saltmarsh to the Greenhouse Gas Registry to track and monitor emissions. 

You can read the groundbreaking report here.