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

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).
  • 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. 

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 10 centimetres 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 tonnes1 – 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.

© Paul Naylor

© Paul Naylor

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 and RSPB are calling 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. 

Mark Dinning, Head of Conservation for Durham Wildlife Trust, says: "Marine environments are so important in supporting life on earth. This report reveals just how vital our seas are for locking away organic carbon with in the sediments of the seabed. It is essential that decision makers recognise the importance blue carbon plays in regulating our climate and protections are put in place that ensure the impacts from human activities on this precious resource are appropriately assessed and regulated. Durham Wildlife Trust has been involved in a number of coastal and marine projects to develop practical solutions to protect marine environments and educate people about the importance of such habitats. This report highlights why these projects are vital tools in the wider challenge of climate change."

Joan Edwards, director of marine policy for The Wildlife Trusts, says: “These world-first reports reveal the enormous value of UK seas, while highlighting that many areas need far better protection. We need strategic decision-making from policymakers to recognise the value of blue carbon by minimising the impact of human activities on the seabed. Damaging activities such as bottom trawling and large development must not take place in protected areas. This research gives the UK an opportunity to lead the world in protecting blue carbon and marine biodiversity.”

Tom Brook, blue carbon specialist at WWF-UK, says: “This project reveals how critical our seas are in regulating the climate and underscores the urgent need to protect and restore our seabed habitats. While saltmarshes and kelp forests punch above their weight in terms of capturing carbon, the mud really is the star here – accumulating and storing vast amounts on the seabed. But we need to make sure it goes undisturbed for it to fulfil this critical function. Harmful activities such as bottom trawling must be stopped.”

Kirsten Carter, head of UK marine policy at the RSPB, says: “Accelerating efforts on land to tackle the nature and climate emergency is critical, but we must not underestimate the role of UK seas. This report is a gamechanger for our knowledge of the marine environment and a huge asset for decision-makers. Now we need them to act on its findings. To meet net zero and stop biodiversity decline we must work with nature, not against it. This means restoring habitats, properly planning offshore development, and investing in protected areas to safeguard wildlife and keep blue carbon locked up.” 

Professor Mike Burrows, Scottish Association for Marine Science, says: “Understanding how much and where our marine carbon is stored is vital for guiding efforts to maintain and protect the capacity of coastal and seabed habitats to continue to serve this function. Saltmarshes and seagrass beds are significant carbon storage hotspots, while kelp beds and especially phytoplankton contribute large amounts of organic carbon annually. However, the exact fraction of this carbon that is stored in sediments remains uncertain. By consolidating various information sources, we have gained valuable insights into our coastal seabed. This process has also highlighted significant gaps in our knowledge regarding the rates of carbon accumulation in sediments.” 

You can read the ground-breaking reports below.

Blue Carbon

*Please note that organic carbon should not be converted into carbon dioxide equivalent in this instance due to the complex interaction of atmospheric carbon and the ocean. 

Editor's notes

The UK’s Blue Carbon Inventory

To access all of the scientific reports and technical summaries in the United Kingdom’s Blue Carbon Inventory visit The Wildlife Trusts' blue carbon webpage. This includes the above for the following areas:

  • UK-wide assessment
  • Scotland report
  • Irish Sea and Welsh Coastal Region
  • English Channel and Western Approaches Region
  • North Sea 

A public report on blue carbon by The Wildlife Trusts, WWF and the RPSB is also available.

The project builds on the English North Sea report, published in 2021. This report was commissioned by the North Sea Wildlife Trusts, Blue Marine Foundation, WWF and the RSPB, and written by SAMS, Cefas, Newcastle University and the University of St Andrews.

Key findings: UK-wide assessment:

  • Organic carbon storage and accumulation: UK seas store an estimated 244 million tonnes of organic carbon (made of living things such as phytoplankton, kelp, and seagrass) in the top 10cm of seabed sediments and vegetated habitats, with over 98% in seabed sediments, principally mud. Some sediments are hundreds of metres thick so the total carbon stored will be far greater. Organic carbon can be released if habitats are disturbed. Up to 13 million tonnes of organic carbon could be added annually to sediment stores where natural sedimentation is able to occur.
  • Inorganic carbon storage: Over 1600 million tonnes of inorganic carbon is stored in the top 10cm of UK marine habitats, mostly as calcium carbonate in shells. As CO2 is released when these materials form, there is no immediate mitigating effect on climate warming.
  • Importance of coastal habitats: Despite covering just 1% of UK seas, saltmarshes, seagrass beds, kelp and intertidal algae contain 1.7% of the total organic carbon, and account for 3.8% of organic carbon accumulated each year. 60% of the carbon is stored in saltmarshes. Since 1860, saltmarshes have declined by 85% in England, in part due to drainage for agriculture, development and coastal defences2.
  • Areas designated for marine protection cover 338,000 km2 (38%) of UK seas. They contain 43% of the total mapped organic carbon and 45% of inorganic carbon. Offshore protected areas are larger than inshore protected areas, and so contain more carbon. Inshore MPAs have the highest densities and rates of organic carbon accumulation per unit area from coastal muds, saltmarshes and seagrass beds.
  • The biggest threats to blue carbon stores come from activities that physically disturb the seabed, predominantly from bottom trawling, but also from moorings and developments at sea and in coastal regions. Bottom trawling can penetrate the seabed, potentially releasing carbon into the atmosphere and harming marine wildlife.
  • Ocean acidification and various climate change impacts pose mixed effects on blue carbon capture, potentially harming calcareous organisms, such as molluscs, while potentially benefiting some photosynthetic species including seaweeds and seagrasses.
  • Oceans catch carbon eroded from land: Seas store carbon that has been eroded on land and transported via waterways such as rivers. Blue carbon stores are the last chance to capture carbon and prevent it from being released into the atmosphere.

 

About UK seas: The UK's EEZ and UK continental shelf (including Rockall) cover an area of 885,000 km. Scotland’s seas cover an area of 617,000 km2, (70% of the UK’s sea area), the English North Sea Region covers an area of 114,000 km2 (13%); the English Channel and Western Approaches Region covers 111,000 km2 (13%); and the Irish Sea and Welsh Coast Region, including the Welsh coastline, covers an area of 43,000 km2 (5%).

About The Blue Carbon Mapping Project 

The Blue Carbon Mapping project was completed by the Scottish Association for Marine Science (SAMS) and funded by WWF-UK in collaboration with The Wildlife Trusts and the RSPB. The reports build on blue carbon mapping that began in Scotland and later in the North Sea. Before the reports were prepared, there was limited coordination of information about how much carbon is stored in UK marine habitats, especially in seabed sediments.

The project was undertaken in phases, divided into regional seas, each with their own report; the English Channel and Western Approaches Region, the Irish Sea and Welsh Coast Region (including Isle of Man territorial waters) and Scotland. This culminated with a UK-wide assessment. The project analysed habitat data as well as primary data from archived sediment samples, and estimates using statistical modelling where data was incomplete.

The study could be critical in helping the UK to meet its commitments to achieve net-zero and protect at least 30% of UK seas by 2030. Understanding more about blue carbon allows policymakers to strategically protect the most important blue carbon stores, and plan activities in UK seas to minimise harm to the marine environment. Blue carbon stores are vulnerable to pressures that can cause them to be disturbed, damaged, or removed entirely. They include bottom-towed fishing gear, used in certain fishing industries such as scallop fishing, moorings, and offshore development.

The analysis considers only surficial sediments for the top 10cm of the seabed. Therefore, the findings represent a fraction of the total carbon stored in the full thickness of sediments, some of which extend hundreds of meters deep and contain millennia’s worth of carbon. 

Blue carbon, as defined in our report, is the term used for carbon captured and/or stored by the world’s ocean and coastal ecosystems. Marine ecosystems capture carbon and lock it away in seabed sediments, especially in vegetated coastal habitats like saltmarsh and seagrass. Saltmarsh and seagrass beds both capture and store carbon whereas seaweeds and kelp forests capture carbon, a proportion of which is then eroded and transported elsewhere as detritus and subsequently buried in seabed sediments. Biogenic reefs act principally as depositories for carbon from other sources. Carbon stores are vulnerable to a variety of human pressures that can cause them to be disturbed, damaged or removed entirely. This can hinder or eliminate their ability to store and/or capture carbon. Long term carbon storage in the sea relies on protecting habitats from damage. Protections also provide other benefits such as providing nursery grounds for fish.

 

References:

  1.  UK forests accumulate an estimated 4.8 million tonnes of carbon per year – Forest Research
     
  2. UK Centre for Ecology & Hydrology: UK saltmarshes 2023 factsheet 
  • 85% of saltmarsh in England has been lost since 1860. 
  • In the UK, there are just 45,000 hectares of saltmarsh remaining.

Partners:

WWF (Worldwide Fund for Nature) is one of the world’s largest independent conservation organisations, active in nearly 100 countries. Our supporters – more than five million of them – are helping us to restore nature and to tackle the main causes of nature’s decline, particularly the food system and climate change. We’re working to ensure a world with thriving habitats and species, and to change hearts and minds so it becomes unacceptable to overuse our planet’s resources. WWF. For your world. For wildlife, for people, for nature. Find out more about our work, past and present at wwf.org.uk .

The Wildlife Trusts (www.wildlifetrusts.org) are a federation of 47 charities, 46 individual Wildlife Trusts and a central charity, the Royal Society of Wildlife Trusts. Together we have more than 900,000 members, 39,000 volunteers and 3,600 staff across the UK. We share a vision of nature in recovery, with abundant, diverse wildlife and natural processes creating wilder landscape where people and nature thrive, and take action, with our communities, to help restore 30% of land and seas for nature by 2030.

The RSPB is the UK’s largest nature conservation charity, protecting habitats, saving species, and helping to end the nature and climate emergency. For over a century we’ve acted for nature through practical conservation and powerful partnerships, campaigning and influence, and inspiring and empowering millions of people, including almost 1.2 million members. Our network of over 200 nature reserves sits at the heart of our world leading science and conservation delivery. Nature is in crisis, but together we can save it. The Royal Society for the Protection of Birds (RSPB) is a registered charity. In England and Wales, no: 207076. In Scotland, no: SC037654. rspb.org.uk.