COAST’S month of Blue Carbon

Each month COAST feature a series of posts on an aspect of our marine ecosystems on their Facebook page. Last month they highlighted the huge role marine ecosystems play in storing carbon – a term known as Blue Carbon – and which can play a vital role in helping to address climate change.

Results of ongoing research, both in Scotland and further afield, are increasing our understanding about the critical role our marine habitats and species play in capturing and storing carbon; as well as informing us about the management decisions required to ensure that the captured carbon in coastal and marine ecosystems – so called ‘Blue Carbon’ – actually stays locked up into the long term.

Blue Carbon infographic – Scottish Parliament SPICe Briefing on Blue Carbon

In Blue Carbon ecosystems, carbon is captured in the living tissue of marine animals and plants and also in their shells and skeletons, such as the shells of scallops and lobsters and coralline seaweed such as maerl. A lot of carbon-based material also gets washed into the sea from the land and this, along with material from marine habitats and plants, can become stored within seabed sediments which then act as a carbon sink and lock the carbon away, potentially for thousands of years. The process of capturing carbon in long-term carbon stores is known as carbon sequestration.

How much carbon is captured and stored by various different marine habitats and species is currently a very active area of research. With marine carbon sequestration estimated at potentially more than double the amount of carbon removed by habitats on land, the marine environment clearly has a significant role to play in our efforts to address climate change. But it can only do this if we look after it and provide more effective protection for marine areas.

Different blue carbon habitats have different features and carbon capture capabilities; here are some of the facts:

* Kelp grows quickly, with new plant material replacing the old growth on an annual basis. Whilst alive, the kelp plants contain short-term carbon stores a then, as the plant material ages, decays and breaks up, some of the material is transport into deeper water where it sinks and contributes to carbon stores held in marine sediments. Kelp can sequester carbon at a rate of 1.7 million tonnes of carbon per year.

* In the top 60cm of known Scottish maerl beds, an estimated 448,000 tonnes of Carbon is stored; research indicates this is a gross underestimate.

* Biogenic reefs in Scotland – an example being the massive flame shell bed divers discovered in the South Arran MPA last year – store up to 142,000 tonnes of Carbon in non-living material.

* There are 355 recorded seagrass sites in Scotland, although the true extent of this key nursery and blue carbon habitat is unknown. Seagrass sequesters carbon at a rate of 1000 tonnes per year; these plants absorb and store carbon 35 times more efficiently than rainforests.

Seagrass, Pipefish on Maerl and biogenic reef flame shell bed. Credit: Howard Wood


Kelp & other seaweeds. Credit: Paul Kay

The oceans contribute to tackling climate change in many ways, and are therefore of great importance to the future health and livelihoods of humans. Seawater absorbs CO2 and heat from the atmosphere: up to a third of the CO2 released into the atmosphere and around 93% of the heat produced as a result of greenhouse gases are being absorbed by our oceans. While this might seem to be a positive thing, warming seas are affecting marine life and our climate and consequently species on land too, and our seas are becoming more acidic as the absorbed carbon dioxide forms carbonic acid. While we cannot just continue to see our oceans as a sponge that can suck up excess heat and greenhouse gases, supporting the ability of marine habitats and species to capture and store carbon as part of their natural function is something we need to encourage.

Blue carbon ecosystems provide many valuable benefits to humans, beyond their carbon storage capabilities. Protecting these areas can provide jobs and income to coastal communities, through recreational opportunities and promotion of nursery habitat for commercial and recreational fisheries. Blue carbon ecosystems provide coastal protection and can help improve water quality, and may are also biodiversity powerhouses, supporting a wealth of life.

If marine ecosystems are damaged or degraded by human activities or natural events, their ability to capture and store carbon is significantly reduced or lost; it can even lead to the rapid release of carbon from the systems, therefore contributing to the climate crisis.

Stored carbon in seabed habitats can be released into the atmosphere by physical disturbance, such as can occur with coastal and marine developments, and through activities such as trawl and dredge fisheries. Such activities can result in release of substantial amounts of carbon, with experts estimating as much as 1.02 billion tons of CO2 is released annually from degraded coastal ecosystems. Earlier this year, findings of a study reported that global trawling releases as much CO2 as air traffic.
With marine carbon sequestration in the UK having an estimated value of £57.5bn annually, improved protection for blue carbon habitats makes economic sense.

Threats to Blue Carbon Ecosystems infographic – Scottish Parliament SPICe Briefing on Blue Carbon


Before and After dredging. Credit: Howard Wood/COAST

Although the Lamlash Bay No Take Zone (NTZ) and South Arran Marine Protected Area (MPA) were initially established to recover and protect marine life, they are also providing important protection for blue carbon habitats such as kelp and other seaweeds, seagrass beds and mud. A study of Scotland’s MPAs estimated carbon capture and storage in the South Arran MPA at 8,046 tonnes per km2 – a total of 2,245,047 tonnes of carbon for the MPA!

The protection of blue carbon habitats is one of the top Nature-based solutions to climate change. As noted throughout this month, blue carbon ecosystems are found wide-spread within Scotland’s Inshore waters. If the Scottish Government were to reinstate an Inshore Limit – via a just transition – to our seas then these vital carbon stores would be protected, helping us combat both climate change and biodiversity loss.

Follow this link to sign the petition to call for the reinstatement of an inshore limit on trawling:

Featured image shows Peacock worm, spiny starfish and brittle stars on maerl. Credit: Howard Wood