Blue carbon refers to carbon captured (sequestered) and stored in coastal (where land meets the sea) and marine (sea) environments. In this briefing, blue carbon refers to carbon sequestered and stored in both living, biological habitats and species and geological sedimentary stores.

Biological blue carbon stores

Biological blue carbon in this briefing encompasses carbon sequestered and stored in coastal habitats (saltmarshes, sand dunes and machair) and marine species and habitats (phytoplankton, kelp, seagrasses, and biogenic reefs). Mangroves are also an important biological blue carbon habitat but are not discussed in this briefing as they do not exist in Scotland.

Biological blue carbon habitats and species directly sequester carbon from the atmosphere and store the carbon in living biological material and, in some cases, in the underlying soil or sediment. These habitats store carbon from just a number of months to thousands of years. After this time, the living biomass decays, releasing the stored carbon back into the water column or atmosphere. Some of the carbon in living material may escape decay after death and become buried in geological blue carbon stores, thereby entering long-term carbon storage.

Ⓒ California Sea Grant (Kelp); Derek Keats (Seagrass); Nature Scot (Biogenic reefs); Keith Hiscock (Maerl beds); European Space Agency (Phytoplankton bloom)

Geological blue carbon stores

Geological blue carbon refers to carbon stored in sediments across Scotland's seafloor or sediments in sea lochs. Geological blue carbon stores contain carbon derived from dead biological material from the marine environment (biological blue carbon) and the terrestrial environment - transported by rivers. Geological systems do not directly sequester carbon from the atmosphere but rather receive carbon from once-living biological systems. Therefore biological and geological blue carbon stores are linked but operate on different timescales. Geological blue carbon stores store carbon for 1,000s - 100,000s of years and are therefore long-term carbon stores.

• Scotland's largest blue carbon store is seafloor sediments.

  • Geological blue carbon stores contain 99.84% (9,620 Mt CO2-eq) of Scotland's blue carbon ¹Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science. which exceeds estimates of the total carbon stored in the terrestrial environment.

  • Scotland's geological blue carbon stores sequester greater quantities of carbon (28.35 Mt CO2-eq per year) than biological blue carbon habitats and species (0.06 Mt CO2-eq per year) and any terrestrial environment. This is primarily due to the large spatial extent of sediments over Scotland's sea floor, which is around six times greater than Scotland's land area.

• Biological blue carbon habitats contribute significantly less to Scotland's blue carbon storage but are important for biodiversity and climate change resilience.

  • Biological blue carbon habitats and species store 0.16% of Scotland's total blue carbon (15.7 Mt CO2-eq).

  • Some biological blue carbon habitats and species, particularly biogenic reefs, have higher carbon sequestration rates on a per unit area basis than geological blue carbon stores or terrestrial habitats. However, their overall contribution to Scotland's annual carbon sequestration is small due to their small spatial extent.

  • Biological blue carbon habitats and species make important contributions to Scotland's biodiversity and resilience to climate change.

Data replotted from: Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.;Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.;Potouroglou, M. (2017). Assessing the role of intertidal seagrasses as coastal carbon sinks in Scotland. Retrieved from https://www.napier.ac.uk/~/media/worktribe/output-975386/assessing-the-role-of-intertidal-seagrasses-as-coastal-carbon-sinks-in-scotland.pdf [accessed 21 February 2021];Mao, J., Burdett , H.L., McGill, R.A., Newton, J., Gulliver, P., & Kamenos, N.A. (2020). Carbon burial over the last four millennia is regulated by both climatic and land use change.. Global Change Biology , 4, 2496-2504.;Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.;Smeaton, C., & Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.

Carbon stored and sequestered by biological blue carbon habitats and species remains an active research area, including within the Scottish Blue Carbon Research Forum.

Carbon store: Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40. Carbon Sequestration:Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.

Saltmarshes are wetland habitats dominated by salt-tolerant vascular plants. Saltmarshes are regularly flooded and drained by salt water brought in by tides. Saltmarshes store carbon in their underlying sediments for up to thousands of years. An assessment of Scottish saltmarshes at Loch Laxford and Kyle of Tongue suggest these environments store carbon for around 1600 years³Barlow, N.L.M., Long, A.J., Saher, M.H., Gehrels, W.R., Garnett, M.H., & Scaife, R.G. (2014). Salt-marsh reconstructions of relative sea-level change in the North Atlantic during the last 2000 years. Quarternary Science Reviews, 99, 1-16. doi: 10.1016/j.quascirev.2014.06.008.

Distribution

The Scottish Saltmarsh Survey, conducted between 2010-2012, estimated that saltmarshes cover 77.04 km2 of Scotland's coast⁴Haynes, T.A. (2016). Scottish saltmarsh survey national report. Scottish Natural Heritage Commissioned Report No. 786.. The largest saltmarshes in Scotland are located in the Solway Firth and Moray Firth. Many smaller saltmarshes are located at the head of sea lochs, bays, and on beaches in northwest Scotland.

Carbon Storage and Sequestration

Carbon storage and sequestration by Scotland's saltmarshes is an active research area through projects like the C-side project and the Scottish Blue Carbon Research Forum. Scotland's saltmarshes store an estimated 2.1 Mt CO2-eq¹Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. This estimate uses averaged organic matter density and saltmarsh depth values, both of which vary spatially across Scotland's saltmarshes.

There are currently no direct measurements of carbon sequestration by Scottish saltmarshes. Based on estimates of carbon sequestration in English saltmarshes⁷Chmura, G.L., Anisfeld, S.C., Cahoon, D.R., & Lynch, J.C. (2003). Global carbon sequestration in tidal, saline wetland soils. Global biogeochemical cycles, 17., Scotland's saltmarshes sequester approximately 0.05 Mt CO2-eq per year²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. This value is potentially an overestimation as it uses an outdated estimate of Scottish saltmarsh area.

Wider importance of saltmarshes

Saltmarshes deliver numerous physical and biological ecosystem benefits. For example, saltmarshes dampen wave energy to reduce flood risk⁹Barbier, E.B., Hacker, S.D., Kennedy, C., Koch, E.W., Stier, A.C., & Silliman, B.R. (2011). The value of estuarine and coastal ecosystem services. Ecological Monographs, 81, 169-183. and filter pollutants from land run-off¹⁰Reboreda, R., & Cacador, I. (2007). Halophyte vegetation influences in salt marsh retention capacity for heavy metals. Environmental Pollution, 146, 147-154.. Providing there is an adequate sediment supply, saltmarshes can keep pace with sea-level rise making their expansion a natural strategy to manage coastlines. In the 2020 Challenge for Scotland's Biodiversity, the Scottish Government highlighted the important role of saltmarshes in resilience and adaptation to climate change.

Saltmarshes also support various bird, plant and invertebrate species and provide key habitats for juvenile fish species¹¹Colclough, S., Fonseca, L., Astley, T., Thomas, K., & Watts, . (2005). Fish utilisation of managed realignments. Fisheries Management and Ecology , 12, 351-360.. Coastal saltmarshes are not generally rich in plant species but are critical for breeding, wintering and migrating birds. The biodiversity richness of saltmarshes makes them popular landscapes for recreational activities such as walking and bird watching.

© Neville Goodman

Carbon storage data: Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.

Distribution

Coastal sand dunes are habitats formed by sand blown inland from beaches, stabilised by vegetation. Sand dunes cover an estimated 495 km2 of Scotland's coast line¹Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40., representing 71% of the UK's sand dunes by area³Angus, S., Hansom, J.D., & Rennie, A. (2011). Habitat Change on Scotland’s Coasts - The Changing Nature of Scotland. Edinburgh: TSO Scotland..

Carbon Storage and Sequestration

Scotland's sand dunes store an estimated 7.4 Mt CO2-eq¹Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.. This estimate considers the carbon stored to a depth of 15 cm in slack (low-lying depressions between dunes), mobile and semi-fixed dune systems. There are currently no estimates for the total carbon sequestration rates across Scotland's sand dunes. However, other UK sand dunes sequester carbon at an estimated rate of 217 g CO2-eq per m2 per year⁵Jones, M.L.M., Sowerby, A., Williams, D.L., & Jones, R.E. (2008). Factors controlling soil development in sand dunes: evidence from a coastal dune soil chronosequence. Plant Soil, 307, 219-234.(for comparison, see Annual Carbon Sequestration per unit area).

Wider importance of sand dunes

Sand dunes provide a rich habitat for biodiversity, supporting birds, reptiles, insects, vascular plants, bryophytes, lichens and fungi. Numerous species listed on the Scottish Biodiversity List, species of conservation priority in Scotland, are found in sand dune habitats.

© Martyn Gorman

Carbon storage: Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.

Distribution

Machair is a form of low-lying dune grassland found in shell-rich sands and is unique to the north-western coasts of Scotland and Ireland²Angus, S., & Hansom, J. (2005). Machair nan Eilean Siar (Machair of the Western Isles). Scottish Geographical Journal , 121, 401-411.. Machair is a highly dynamic habitat and varies in response to climate variations and changing land-use. Scotland has an estimated 200 km2 of machair, mainly in South Uist (a designated Special Area of Conservation³Burrows, M.T., Hughes, D.J., Austin, W.E.N., Smeaton, C., Hicks, N., Howe, J.A., … Vare, L.L. (2017). Assessment of Blue Carbon Resources in Scotland’s Inshore Marine Protected Area Network. Scottish Natural Heritage Commissioned Report No. 957.).

Carbon Storage and Sequestration

Scotland's machair environments store approximately 2.50 Mt CO2-eq¹Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., & Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40. based on machair samples to 0.15 m depth. There are no estimates of carbon sequestration rates across the total area of Scotland's machair. However, work is ongoing by NatureScot to produce better estimates of machair carbon sequestration.

Wider importance of Machair

Machair supports high plant and animal diversity, most notably flowers and birds. Machair contains many rare flower species such as lesser-butterfly orchid, Hebridean spotted orchid and marsh orchid. Machair is an important breeding ground for birds such as lapwing, redshank, snipe and dunlin in wetter areas and oystercatcher and ringed plover on cultivated areas.

Ⓒ Jon Thomson

Carbon storage: Potouroglou, M. (2017). Assessing the role of intertidal seagrasses as coastal carbon sinks in Scotland. Retrieved from https://www.napier.ac.uk/~/media/worktribe/output-975386/assessing-the-role-of-intertidal-seagrasses-as-coastal-carbon-sinks-in-scotland.pdf [accessed 21 February 2021] Carbon sequestration:Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.

Distribution

Seagrasses (also known as eelgrasses) are flowering plants that form dense meadows or beds under the sea. Seagrasses can also occupy the intertidal zone (the area of land covered at high tide and uncovered at low tide). Recent estimates predict that Scotland's seagrass area is 21.64 km2, 95% of which is found in the Scottish Highlands³Green, A.E., Unsworth, R.K., Chadwick, M.A., & Jones, P.J. (2021). Historical analysis exposes catastrophic seagrass loss for the United Kingdom. Frontiers in Plant Science, 12, 261.. This area represents a 58% reduction in seagrass coverage since 1936³Green, A.E., Unsworth, R.K., Chadwick, M.A., & Jones, P.J. (2021). Historical analysis exposes catastrophic seagrass loss for the United Kingdom. Frontiers in Plant Science, 12, 261. driven by changes in land-use.

Carbon Storage and Sequestration

Scottish seagrass carbon storage and sequestration remains an ongoing area of research. The majority of carbon in seagrass ecosystems is stored within the underlying sediment rather than in the living seagrasses⁵Fourqurean, J.W., Duarte, C.M., Kennedy, H., Marba, N., Holmer, M., Matero, M.A., … Serrano, O. (2012). Seagrass ecosystems as a globally significant carbon stock. Nature, 5, 505-509.. Scotland's seagrasses store an estimated 0.3 Mt CO2-eq¹Potouroglou, M. (2017). Assessing the role of intertidal seagrasses as coastal carbon sinks in Scotland. Retrieved from <a href="https://www.napier.ac.uk/~/media/worktribe/output-975386/assessing-the-role-of-intertidal-seagrasses-as-coastal-carbon-sinks-in-scotland.pdf" target="_blank">https://www.napier.ac.uk/~/media/worktribe/output-975386/assessing-the-role-of-intertidal-seagrasses-as-coastal-carbon-sinks-in-scotland.pdf</a> [accessed 21 February 2021].

Based on global seagrass sequestration rates, Scottish seagrasses sequester approximately 0.005 Mt CO2 -eq per year²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. This estimate is uncertain as seagrass sequestration rates depend on species, and have not been directly measured in Scottish seagrasses.

Replotted data from Geodatabase of Marine features adjacent to Scotland (GeMS) (V9i25) © NatureScot and JNCC

Wider importance of seagrass

Seagrass meadows provide habitats, nursery areas, food and shelter for a diverse range of species, such as the pipefish (a relative of the seahorse) and commercial fish like cod, plaice, pollock, and oysters⁸Beck , M.W., Heck, K.L., Able, K.W., Childers, D.L., Eggleston, D.B., Gillanders, B.M., … Orth, R.J. (2001). The identification, conservation, and management of estuarine and marine nurseries for fish and invertebrates: a better understanding of the habitats that serve as nurseries for marine species and the factors that create site-specific variability in nursery quality will improve conservation and management of these areas. Bioscience, 51, 633-641.. Seagrass roots also stabilise the underlying sediment and absorb wave and current energy, thereby reducing coastal erosion and playing a role in climate change resilience⁹Lilley, R. (2017). Our Living Seas – Scotland’s Seagrass Meadows. Retrieved from <a href="https://scottishwildlifetrust.org.uk/2017/06/living-seas-scotlands-seagrass-meadows/" target="_blank">https://scottishwildlifetrust.org.uk/2017/06/living-seas-scotlands-seagrass-meadows/</a> [accessed 13 2021].

Ⓒ Howard Wood/COAST

Carbon storage: Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.

Biogenic reefs are solid structures raised above the sea bed formed by accumulations of organisms that build dense inorganic carbon (calcium carbonate) structures, which acts as the predominant carbon store. The following marine habitats in Scottish waters are considered biogenic reefs:

• Maerl and Maerl beds (See Maerl beds)

• Cold-water coral reefs

• Tubeworm reefs (also known as serlupid reefs or aggregations)

• Flame shell beds

• Horse mussel beds

• Blue mussel beds

• Brittlestar beds

• Native oyster beds

© Marine Scotland (Flame shell beds, Cold-water corals); Nature Scot (Serpulid reefs);JNCC (Horse mussel beds); Keith Hiscock (Brittlestar beds).

Distribution

Biogenic reefs form at a range of depths from the shallow waters to the deep sea (up to 1500m). The total extent of biogenic reefs in Scotland's seas remains uncertain, as there has yet to be a comprehensive assessment of their distribution. This is especially true in Scotland's deep sea (100 - 1500 m). Reefs can also form in lochs. For instance, tubeworm reefs cover 1 km2 in Loch Creran²Moore , C.J., Bates, C.R., Mair, J.M., Saunders, G.R., Harries, D.B., &amp; Lyndon, A.R. (2009). Mapping serpulid worm reefs (Polychaeta: Serpulidae) for conservation management. Aquatic Conservation: Marine and Freshwater Ecosystems, 19, 226-236.. Based on available records, biogenic reefs (excluding maerl beds considered later in this briefing) cover an estimated 20.5 km2 in Scottish waters. However total biogenic reef area is highly uncertain and remains an ongoing research area¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh..

Data replotted from Geodatabase of Marine features adjacent to Scotland (GeMS) (V9i25) © NatureScot and JNCC

Carbon Storage and Sequestration

Biogenic reefs (excluding Maerl beds) store an approximate 0.5 Mt CO2 -eq¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. However, this value remains uncertain as the true spatial extent of biogenic reefs is not known. There are little area and carbon storage data of blue mussel beds, the native oyster, and brittlestar beds. Cold-water corals alone are estimated to constitute 86% of the estimated carbon storage of biogenic reefs. The majority of this carbon storage is found in the Darwin Mounds, a Special Area of Conservation, situated off Scotland's north-west coast.

There is currently no estimate of the total carbon sequestered annually by biogenic reefs across Scotland's seas (this does not include Maerl beds). This is primarily due to the uncertainty of biogenic reef spatial extent. However, estimates of biogenic reef sequestration rates per unit area do exist and range between 129-1541 g CO2-eq per m2 per year¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.⁶Migne, A., Davoult, D., &amp; Gattuso, J.P. (1998). Calcium carbonate production of a dense population of the brittle star Ophiothrix fragilis (Echinodermata: Ophiuroidea): role in the carbon cycle of a temperate coastal ecosystem. Marine Ecology Progress Series, 173, 305-308.. These values indicate that on a per unit basis biogenic reefs have some of the highest carbon sequestration rates of all blue carbon and terrestrial habitats.

Carbon storage: Mao, J., Burdett , H.L., McGill, R.A., Newton, J., Gulliver, P., & Kamenos, N.A. (2020). Carbon burial over the last four millennia is regulated by both climatic and land use change.. Global Change Biology , 4, 2496-2504.Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh. Carbon sequestration: Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.Mao, J., Burdett , H.L., McGill, R.A., Newton, J., Gulliver, P., & Kamenos, N.A. (2020). Carbon burial over the last four millennia is regulated by both climatic and land use change.. Global Change Biology , 4, 2496-2504.

Maerl is the collective name for pink-purple algae that produce hard, inorganic carbon exterior skeletons. Maerl form extensive 3D underwater deposits known as maerl beds, formed of living and dead maerl. Similarly to phytoplankton, maerl store carbon in their soft biomass (organic carbon) and in their external skeletons (inorganic carbon). Living maerl is extremely slow-growing (around 0.25 mm per year)²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh. and can live for up to 100 years⁶Foster, M.S. (2001). Rhodoliths: between rocks and soft places. Journal of Phycology , 27, 659-667.. Scottish maerl beds can be thousands of years old - a maerl bed in the Sound of Iona is estimated to be around 4,000 years old⁷Hall-Spencer, J.M., Grall, J., Moore, P.G., &amp; Atkinson, R.J.A. (2003). Bivalve fishing and maerl‐bed conservation in France and the UK—retrospect and prospect. Aquatic Conservation: Marine and Freshwater Ecosystems, 13, 33-41..

Distribution

Maerl and maerl beds occur in abundance along Scotland's west coast, Orkney and Shetland, but are nearly absent from the east coast⁸Scottish Government. (2017). Review of PMFs outside the Scottish MPA network - Maerl beds. Retrieved from <a href="https://consult.gov.scot/marine-scotland/priority-marine-features/supporting_documents/Review%20of%20PMFs%20outside%20the%20Scottish%20MPA%20network%20%20FINAL%20%20Maerl%20beds.pdf" target="_blank">https://consult.gov.scot/marine-scotland/priority-marine-features/supporting_documents/Review%20of%20PMFs%20outside%20the%20Scottish%20MPA%20network%20%20FINAL%20%20Maerl%20beds.pdf</a> [accessed 13 February 2021]. Based on the 353 records of maerl beds in Scotland, maerl and maerl beds cover an estimated 7.06 km2. This value is potentially an underestimate if some maerl beds remain undiscovered, which is likely.

Data replotted from Geodatabase of Marine features adjacent to Scotland (GeMS) (V9i25) © NatureScot and JNCC

Carbon Storage and Sequestration

Maerl beds store an estimated 1.6 Mt CO2-eq¹Mao, J., Burdett , H.L., McGill, R.A., Newton, J., Gulliver, P., &amp; Kamenos, N.A. (2020). Carbon burial over the last four millennia is regulated by both climatic and land use change.. Global Change Biology , 4, 2496-2504.²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh., predominately as inorganic carbon in live and dead maerl skeletal material. Maerl bed carbon storage estimates depend on bed thickness, for which very little extensive data exist. Current estimates use an average bed thickness of 60 cm²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh., but beds can be thicker: beds as thick as 125 cm are documented in the Wyre Sound¹²Porter, J., Austin, W.E.N., Burrows, M.T., Clarke, D., Davies, G., Kamenos, N., … Want, A. (2020). Blue carbon audit of Orkney waters. Scottish Marine and Freshwater Science, 11, 96.¹³Marine Scotland . (2020). Scotland's Marine Assessment 2020: Case Study Blue Carbon Scottish Maerl Beds. Retrieved from <a href="https://marine.gov.scot/sma/assessment/case-study-blue-carbon-scottish-maerl-beds" target="_blank">https://marine.gov.scot/sma/assessment/case-study-blue-carbon-scottish-maerl-beds</a> [accessed 13 February 2021]. In addition, a large volume of dead maerl deposits are washed up as beach sediments and are therefore not included in the calculation of maerl carbon stores. These uncertainties indicate that maerl and maerl bed carbon storage is potentially underestimated.

Maerl beds sequester an estimated 0.002 Mt CO2-eq per year²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.¹Mao, J., Burdett , H.L., McGill, R.A., Newton, J., Gulliver, P., &amp; Kamenos, N.A. (2020). Carbon burial over the last four millennia is regulated by both climatic and land use change.. Global Change Biology , 4, 2496-2504.. Carbon sequestration rates depend on the percentage of living maerl within maerl beds, for which no extensive data currently exist. Current estimates use a value of 50% living maerl in carbon sequestration rate calculations. However, observations show that living maerl in the bed surface layer can vary between 5%-100%²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.indicating that this is a source of uncertainty in sequestration rate calculations.

Wider importance of maerl beds

Maerl beds are ideal conditions for developing diverse communities of plants and animals on, between, and under maerl pieces. Other seaweeds, sea firs (hydroids), sea urchins, brittle stars, starfish, sea anemones and scallops may colonise the surface of the bed. Small crabs, queen scallops, and juvenile fish can hide inside the bed while burrowing crabs, worms, and bivalves live in the sediment below. For example, in the Firth of Clyde, greater numbers of cod were found in shallow sheltered areas where the seabed was composed of maerl-containing gravels and pebbles¹⁷Elliott, S.A., Turrell, W.R., Heath, M.R., &amp; Bailey, D.M. (2017). Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras. Marine Ecology Progress Series , 568, 123-135.. Maerl beds are also a nursery habitat for commercially important shellfish, such as scallops¹⁸Kamenos, N.A., Moore, P.G., &amp; Hall-Spencer, J.M. (2004). Small-scale distribution of juvenile gadoids in shallow inshore waters; what role does maerl play?. ICES journal of marine science, 61, 422-429..

Ⓒ Keith Hiscock

Carbon sequestration: Turrell, W.R. (2020). A Compendium of Marine Related Carbon Stores, Sequestrations and Emissions. Scottish Marine and Freshwater Science Vol 11 No 1, 70pp. Retrieved from https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissionsBurrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.

Distribution

Phytoplankton are microscopic, single-celled marine algae (seaweed) that live in the sea surface. Phytoplankton are ubiquitous in Scotland's seas and therefore cover the total extent of Scotland's seas (469, 960 km2).

Carbon Storage and Sequestration

Phytoplankton sequester both organic and inorganic carbon. Phytoplankton rapidly degrade in surface waters and therefore it is difficult to estimate the carbon stored by phytoplankton biomass at any given time. As such, there are currently no accurate estimates of living phytoplankton carbon storage.

Following death, around 90% of phytoplankton biomass degrades, releasing carbon back into the seawater and atmosphere²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. The remaining 10% of phytoplankton biomass escapes degradation and is buried in seafloor sediments, thereby contributing to long-term carbon storage. Phytoplankton biomass entering long-term (sediment) carbon storage sequesters an estimated 14.3 Mt CO2-eq per year¹Turrell, W.R. (2020). A Compendium of Marine Related Carbon Stores, Sequestrations and Emissions. Scottish Marine and Freshwater Science Vol 11 No 1, 70pp. Retrieved from <a href="https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions" target="_blank">https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions</a>²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. The key uncertainty in this estimate is the proportion of phytoplankton biomass which escapes degradation and is buried in seafloor sediments. This remains an ongoing research area.

Ⓒ European Space Agency

Distribution

Kelp is the generic name for several species of large, brown (macro)algal seaweed. Kelp grows in underwater communities known as kelp forests or beds. Kelp also accumulates near to or just below the shore on sediments (known as sublittoral sediments). Kelp beds are widely recorded around the coasts of Scotland's mainland and islands, covering an estimated 3747 km2 of Scotland's coast¹Burrows, M.T., Fox, C.J., Moore, P., Smale, D., Sotheran, I., Benson, A., … Allen, C.J. (2018). Wild Seaweed Harvesting as a Diversification Opportunity for Fishermen. A report by SRSL for HIE, 171..

Data replotted from Geodatabase of Marine features adjacent to Scotland (GeMS) (V9i25) © NatureScot and JNCC

Carbon Storage and Sequestration

Carbon is only stored in the living kelp and not in the underlying beds and sediments. Living kelp in Scotland stores an estimated 1.2 Mt CO2-eq²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. This value is uncertain as kelp productivity depends on algal species, habitat, depth, light and nutrient levels³Mann, K.H. (2000). Ecology of coastal waters: with implications for management. Oxford: Blackwell Science.⁴Smale, D. A., Burrows, M. T., Moore, P., O'Connor, N., &amp; Hawkins, S. J. (2013). Threats and knowledge gaps for ecosystem services provided by kelp forests: a northeast Atlantic perspective. Ecology and Evolution, 3(11), 4016-4038. DOI: 10.1002/ece3.774. Retrieved from: https://pure.qub.ac.uk/portal/files/5970848/Smale_et_al_13.pdf [accessed 29th October 2018].⁵Smale, D.A., Burrows, M.T., Evans, A.J., King, N., Sayer, M.D., Yunnie, A.L., … Moore, P.J. (2016). Linking environmental variables with regional-scale variability in ecological structure and standing stock of carbon within UK kelp forests. Marine Ecology Progress Series, 542, 79-95.. Research is ongoing to improve estimates of carbon stored in Scotland's living kelp.

Following death, the carbon in kelp biomass can enter the wider marine microbial food web. As with phytoplankton, the majority of kelp-derived carbon degrades, releasing the stored carbon. A much smaller proportion of kelp escapes degradation and is buried in seafloor sediments, contributing to long-term carbon sequestration⁶Krause-Jenson, D., &amp; Duarte, C. (2016). Substantial role of macroalgae in marine carbon sequestration. Nature Geoscience, 9, 737-742.⁷Ortega, A., Geraldi, N.R., Alam, I., Kamau, A.A., Acinas, S.G., Logares, R., … Duarte, C.M. (2019). Important contribution of macroalgae to oceanic carbon sequestration. Nature Geoscience, 12, 748-754.. Globally, an estimated 11.4% of kelp-derived carbon enters long-term storage, which results in a kelp sequestration rate of 0.7 Mt CO2-eq per year²Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.⁶Krause-Jenson, D., &amp; Duarte, C. (2016). Substantial role of macroalgae in marine carbon sequestration. Nature Geoscience, 9, 737-742..

Wider importance of kelp

Kelp carbon storage and sequestration is only one aspect of their importance. The sheltered areas beneath kelp are important habitats for marine biodiversity. Kelp beds support a range of species, including sea anemones, sea firs, sea squirts, sponges and a variety of other seaweeds. Within the UK alone, more than 1800 species of flora and fauna have been recorded from kelp-dominated habitats⁴Smale, D. A., Burrows, M. T., Moore, P., O'Connor, N., &amp; Hawkins, S. J. (2013). Threats and knowledge gaps for ecosystem services provided by kelp forests: a northeast Atlantic perspective. Ecology and Evolution, 3(11), 4016-4038. DOI: 10.1002/ece3.774. Retrieved from: https://pure.qub.ac.uk/portal/files/5970848/Smale_et_al_13.pdf [accessed 29th October 2018].. Kelp forests also provide nursery grounds for commercial fish and shellfish and can support species at higher trophic levels (further up the food chain), including cetaceans, seals, otters and birds¹¹Shaffer, J.A., Munsch, S.H., &amp; Cordell, J.R. (2020). Kelp Forest Zooplankton, Forage Fishes, and Juvenile Salmonids of the Northeast Pacific Nearshore. Marine and Coastal Fisheries, 12, 4-20.. Kelp-based ingredients are widely employed in agricultural, chemical, cosmetic and food applications. Kelp harvesting is the subject of another SPICe briefing.

Ⓒ Mike Deaton

Marine sediments accumulating on the ocean floor store large quantities of carbon over long periods, typically between thousands to hundreds of thousands of years. Marine sediments do not directly sequester carbon but receive organic and inorganic carbon from biological blue carbon habitats or terrestrial environments.

While terrestrial carbon stores, such as forests, are well-mapped and have robust protocols for carbon stock assessments and accounting¹Gibbs, H.K., Brown, S., Niles, J.O., &amp; Foley, J.A. (2007). Monitoring and estimating tropical forest carbon stocks: making REDD a reality. Environmental Research Letters, 2, 45023., relatively little of the seabed has been mapped²Diesing , M., Mitchell, P., &amp; Stephens, D. (2016). Image-based seabed classification: what can we learn from terrestrial remote sensing?. ICES Journal of Marine Science, 73, 2425-2441.. Ongoing research within the Scottish Blue Carbon Forum aims to quantify carbon sequestration and storage in Scottish seafloor and sea loch sediments³Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.⁴Smeaton, C., &amp; Austin, W.E.N. (2019). Where’s the Carbon: Exploring the Spatial Heterogeneity of Sedimentary Carbon in Mid-Latitude Fjords. Frontiers in Earth Science, 7, 269.⁵Smeaton, C., &amp; Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.⁶Hunt, C., Demsar, U., Dove, D., Smeaton, C., Cooper, R., &amp; Austin, W.E.N. (2020). Quantifying Marine Sedimentary Carbon: A New Spatial Analysis Approach Using Seafloor Acoustics, Imagery, and Ground-Truthing Data in Scotland. Frontiers in Marine Science , 7..

The top 10 cm of seafloor sediments covering Scotland's seas store an estimated 9586 Mt CO2-eq¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. The majority of the carbon in seafloor sediments (85%) is inorganic carbon derived from dead shell material. The remaining 15% is organic carbon.

The density of carbon in Scotland's seafloor sediments (measured in kg carbon per cubic meter) is highly variable. The greatest carbon densities surround Scotland's Northern Isles (inorganic carbon) and the inshore marine environment off Scotland's western coast (organic carbon)¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. The total carbon stored deeper than 10cm is uncertain, as there are limited data available on sediment thickness and carbon density below surface sediments. This remains an ongoing research area within the Scottish Blue Carbon Research Forum. The carbon storage estimate of 9586 Mt CO2-eq is therefore potentially only a fraction of full-thickness sedimentary carbon stocks.

Data replotted from Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.

Data replotted from Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.

Seafloor sediments sequester an estimated 28.2 CO2-eq per year¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. There is a degree of uncertainty in this value as it is based on sequestration rates in Northern European seas (e.g. Norway) and isolated measurements from single studies¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. The majority of seafloor carbon sequestration is from organic carbon (26.4 CO2-eq per year), with a lower contribution from inorganic carbon (1.8 CO2-eq per year)¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. Most of the organic carbon sequestration into seafloor sediments is from phytoplankton (68.4%) biomass, with the remaining carbon derived from kelp¹Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. However, the precise contribution of these sources to organic carbon sequestration in sediments remains a key source of uncertainty and is an area of ongoing research.

Data replotted from Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.

Carbon Storage: Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science. Carbon Sequestration: Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.Turrell, W.R. (2020). A Compendium of Marine Related Carbon Stores, Sequestrations and Emissions. Scottish Marine and Freshwater Science Vol 11 No 1, 70pp. Retrieved from https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions

Sea lochs or fjords (herein referred to as sea lochs) are sea inlets that extend inland. Scotland's sea lochs cover 2,608 km2¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science. primarily along Scotland's western coast and islands.

Carbon Storage and Sequestration

Sea lochs are long-term stores of both inorganic and organic carbon, storing carbon for thousands to tens of thousands of years. Sea lochs store an estimated 33.8 Mt CO2-eq¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. As with seafloor sediments, sea loch carbon density varies over their area, depending mainly on sediment type⁶Smeaton, C., &amp; Austin, W.E.N. (2019). Where’s the Carbon: Exploring the Spatial Heterogeneity of Sedimentary Carbon in Mid-Latitude Fjords. Frontiers in Earth Science, 7, 269..

Scotland's sea lochs have greater organic carbon densities than Scotland's seafloor sediments⁷Smeaton, C., &amp; Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.⁸Diesing, M., Kroger, S., Parker, R., Jenkins, C., Mason, C., &amp; Weston, K. (2017). Predicting the standing stock of organic carbon in surface sediments of the North–West European continental shelf. Biogeochemistry, 135, 183-200. and as such sea lochs are considered organic carbon 'hotspots'¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. The proximity of sea lochs to the terrestrial environment allows them to capture organic material from forest and peatland ecosystems as it is washed out to sea⁷Smeaton, C., &amp; Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.. Up to 40% of organic carbon in sea lochs originates from terrestrial ecosystems⁷Smeaton, C., &amp; Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.. Sea lochs are prone to periods of low oxygen, which further promotes organic carbon preservation in sediments¹²Gillibrand, P.A., Cromey, C.J., Black, K.D., Inall, M.E., &amp; Gontarek, S.J. (2006). Identifying the risk of deoxygenation in Scottish sea lochs with isolated deep water. Scottish Aquaculture Research Forum, SARF, 7.. The high proportion of organic carbon in sea loch sediments means that they are sensitive to carbon release through physical disturbances. Sea loch sediments sequester an approximate 0.15 Mt CO2-eq per year⁷Smeaton, C., &amp; Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768..

Data replotted from Smeaton, C., & Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.,Diesing, M., Kroger, S., Parker, R., Jenkins, C., Mason, C., & Weston, K. (2017). Predicting the standing stock of organic carbon in surface sediments of the North–West European continental shelf. Biogeochemistry, 135, 183-200.,Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.,Smeaton, C., & Austin, W.E.N. (2019). Where’s the Carbon: Exploring the Spatial Heterogeneity of Sedimentary Carbon in Mid-Latitude Fjords. Frontiers in Earth Science, 7, 269.

Carbon Stores

Geological sediments (seafloor and sea loch sediments) store the majority (99.84%) of Scotland's blue carbon, totalling 9,620.2 Mt CO2-eq¹Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. This exceeds estimates of carbon storage in Scottish peatlands ²Turrell, W.R. (2020). A Compendium of Marine Related Carbon Stores, Sequestrations and Emissions. Scottish Marine and Freshwater Science Vol 11 No 1, 70pp. Retrieved from <a href="https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions" target="_blank">https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions</a>³Chapman, S.J., Bell, J., Donnelly, D., &amp; Lilly, A. (2009). Carbon stocks in Scottish peatlands. Soil Use and Management, 25, 105-112.(5,945 Mt CO2-eq), forestry (2,050 Mt CO2-eq in living trees and underlying soil)⁴Forestry Commission. (2020). Forestry Statistics 2020. Retrieved from <a href="https://www.forestresearch.gov.uk/documents/7806/CompleteFS2020.pdf" target="_blank">https://www.forestresearch.gov.uk/documents/7806/CompleteFS2020.pdf</a> [accessed 12 February 2021] and non-peatland soils (1,550 Mt CO2-eq)²Turrell, W.R. (2020). A Compendium of Marine Related Carbon Stores, Sequestrations and Emissions. Scottish Marine and Freshwater Science Vol 11 No 1, 70pp. Retrieved from <a href="https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions" target="_blank">https://data.marine.gov.scot/dataset/compendium-marine-related-carbon-stores-sequestrations-and-emissions</a>⁶Aitkenhead, M.J., &amp; Coull, M.C. (2016). Mapping soil carbon stocks across Scotland using a neural network model. Geoderma, 15, 187-198..

Annual Carbon Sequestration

Scotland's geological blue carbon stores (seafloor sediments and sea loch sediments) sequester an estimated 28.35 Mt CO2-eq per year⁷Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. Biological blue carbon habitats and species (e.g. seagrass, maerl beds,biogenic reefs, saltmarshes) sequester significantly less (0.06 Mt CO2-eq per year) primarily due to their much smaller area.

Current estimates predict that Scotland's forests sequester 9.6-11 Mt CO2-eq per year⁸Thistlethwaite, G., Smith, H., Brown, P., MacCarthy, J., Pang, Y., Passant, N., … Misselbrook, T. (2020). Report: Greenhouse Gas Inventories for England, Scotland, Wales &amp; Northern Ireland: 1990-2018. Retrieved from <a href="https://naei.beis.gov.uk/reports/reports?report_id=1000" target="_blank">https://naei.beis.gov.uk/reports/reports?report_id=1000</a>⁹Forestry Commission . (2018). Forestry Statistics 2018: Chapter 4: UK Forests and Climate Change. Retrieved from <a href="https://www.forestresearch.gov.uk/documents/5267/ch4_climatechange_FS2018.pdf" target="_blank">https://www.forestresearch.gov.uk/documents/5267/ch4_climatechange_FS2018.pdf</a> [accessed 17 2021]. This value only considers living trees and is likely to be greater if forestry soil is included. Healthy peatlands can sequester large quantities of carbon, but currently around 80% of Scottish peatland are in a degraded state¹⁰Scotland's Soils. (2019). Peatland restoration. Retrieved from <a href="https://soils.environment.gov.scot/resources/peatland-restoration/#:~:text=Scotland%27s%20peat%20soils%20cover%20more,storing%20carbon%20in%20the%20soil." target="_blank">https://soils.environment.gov.scot/resources/peatland-restoration/#:~:text=Scotland%27s%20peat%20soils%20cover%20more,storing%20carbon%20in%20the%20soil.</a> [accessed 22 February 2021]. As such, Scottish peatlands are a carbon source; it is estimated that peatlands emit 6-10 Mt CO2-eq per year¹¹Climate Change Committee. (2020). Reducing emissions in Scotland – 2020 Progress Report to Parliament. Retrieved from <a href="https://www.theccc.org.uk/publication/reducing-emissions-in-scotland-2020-progress-report-to-parliament/" target="_blank">https://www.theccc.org.uk/publication/reducing-emissions-in-scotland-2020-progress-report-to-parliament/</a>. New preliminary estimates published in February 2021 suggest that Scotland's peatlands emitted 7.7 Mt CO2-eq in 2018¹²Scottish Government. (2021, February). Scottish Greenhouse Gas Statistics: Future revisions to data associated with the incorporation of the IPCC Wetlands Supplement (2013) . Retrieved from <a href="https://www.gov.scot/binaries/content/documents/govscot/publications/statistics/2021/02/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/documents/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/govscot%3Adocument/GHG_2021_02.pdf" target="_blank">https://www.gov.scot/binaries/content/documents/govscot/publications/statistics/2021/02/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/documents/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/future-revisions-to-scottish-greenhouse-gas-statistics-associated-with-ipcc-wetlands-supplement/govscot%3Adocument/GHG_2021_02.pdf</a> [accessed 18 March 2021], with a final estimate expected to be published by the Scottish Government in June 2021.

For comparison, Scotland's annual greenhouse gas (GHG) emissions in 2018 were 41.6 Mt CO2-eq per year¹³Scottish Government. (2018). Greenhouse gas emissions 2018: estimates. Retrieved from <a href="https://www.gov.scot/publications/scottish-greenhouse-gas-emissions-2018/pages/1/" target="_blank">https://www.gov.scot/publications/scottish-greenhouse-gas-emissions-2018/pages/1/</a> [accessed 13 February 2021]. It is important to note that Scotland's GHG emissions and peatland emissions also include other forms of carbon, such as methane (CH4).

Data replotted from: Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.,Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.,Smeaton, C., & Austin, W.E.N. (2019). Where’s the Carbon: Exploring the Spatial Heterogeneity of Sedimentary Carbon in Mid-Latitude Fjords. Frontiers in Earth Science, 7, 269.,Smeaton, C., & Austin, W.E.N. (2017). Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords. Journal of Geophysical Research: Biogeosciences, 122, 2754-2768.,Chapman, S.J., Bell, J., Donnelly, D., & Lilly, A. (2009). Carbon stocks in Scottish peatlands. Soil Use and Management, 25, 105-112.,Forestry Commission . (2018). Forestry Statistics 2018: Chapter 4: UK Forests and Climate Change. Retrieved from https://www.forestresearch.gov.uk/documents/5267/ch4_climatechange_FS2018.pdf [accessed 17 2021],Scottish Government. (2018). Greenhouse gas emissions 2018: estimates. Retrieved from https://www.gov.scot/publications/scottish-greenhouse-gas-emissions-2018/pages/1/ [accessed 13 February 2021],Forestry Commission. (2020). Forestry Statistics 2020. Retrieved from https://www.forestresearch.gov.uk/documents/7806/CompleteFS2020.pdf [accessed 12 February 2021],Aitkenhead, M.J., & Coull, M.C. (2016). Mapping soil carbon stocks across Scotland using a neural network model. Geoderma, 15, 187-198.,Climate Change Committee. (2020). Reducing emissions in Scotland – 2020 Progress Report to Parliament. Retrieved from https://www.theccc.org.uk/publication/reducing-emissions-in-scotland-2020-progress-report-to-parliament/

Annual carbon sequestration rates (Mt CO2-eq per year) depend on the blue carbon habitat area, which remains uncertain for some habitats in Scotland's seas (e.g. biogenic reefs). It is useful to also compare annual carbon sequestration per square metre (measured in grams CO2 per m2 per year), which does not require an estimate of total habitat area. Annual carbon sequestration per unit area is also a useful indicator of how carbon sequestration density varies between terrestrial and marine habitats. In other words, this metric can identify which environments are the most efficient at sequestering carbon on a per unit area basis.

Biological blue carbon sequestration rates are highly variable, ranging between 128.1 (Machair) to 1541.4 g CO2-eq per m2 per year (Tubeworm reefs). Despite displaying some of the highest carbon sequestration rates on a per unit area basis, these habitats contribute minimally to Scotland's overall carbon sequestration due to their small spatial extent in Scotland's seas.

Of the geological carbon stores, sea lochs sequester 3.5 times more carbon (on a per unit area basis) compared with seafloor sediments (both inshore and offshore sediments). Seafloor sediments in inshore environments sequester a greater amount of carbon annually per square metre (159.3 g CO2-eq per m2 per year) compared to sediments in offshore environments (3.85 g CO2-eq per m2 per year).

Terrestrial Environments

Scottish Forestry estimates that healthy Scottish forestry (not including soil carbon sequestration) can sequester between 190 - 700 g CO2 per m2 per year²⁹Scottish Forestry . (2020). Climate Mitigation: Woodland creation and management. Retrieved from <a href="https://forestry.gov.scot/publications/973-information-note-climate-mitigation-woodland-creation-and-management/viewdocument" target="_blank">https://forestry.gov.scot/publications/973-information-note-climate-mitigation-woodland-creation-and-management/viewdocument</a>. Currently, 80% of Scottish peatlands are in a degraded state³⁰The James Hutton Institute. (2016). Peatlands. Retrieved from <a href="https://www.hutton.ac.uk/sites/default/files/files/publications/Peatlands%20final_web_reduced%20size.pdf" target="_blank">https://www.hutton.ac.uk/sites/default/files/files/publications/Peatlands%20final_web_reduced%20size.pdf</a> [accessed 2 March 2021]. However, healthy, restored peatlands can sequester 48 - 280 g CO2 per m2 per year³¹Artz, R.R.E., Chapman, S.J., Donnelly, D., &amp; Matthews, R.B. (2011). Potential Abatement from Peatland Restoration. Retrieved from <a href="https://www.climatexchange.org.uk/media/1501/research_summary_potential_abatement_from_peatland_restoration.pdf" target="_blank">https://www.climatexchange.org.uk/media/1501/research_summary_potential_abatement_from_peatland_restoration.pdf</a> [accessed 17 February 2021]³²Clymo , R.S., Turunen , J., &amp; Tolonen, K. (1998). Carbon Accumulation in Peatland. Oikos, 81, 368-388..

Taken together, these estimates indicate that numerous blue carbon habitats (in particular, biogenic reefs) annually sequester more carbon on a per unit basis, compared to terrestrial habitats. As such, blue carbon habitats are globally considered to be attractive nature-based solutions to climate change, but research is still ongoing in Scotland to determine their viability as a climate change mitigation strategy.

Blue carbon data replotted from Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., & Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.,Jones, M.L.M., Sowerby, A., Williams, D.L., & Jones, R.E. (2008). Factors controlling soil development in sand dunes: evidence from a coastal dune soil chronosequence. Plant Soil, 307, 219-234.,McLeod, E., Chmura , G., Bouillon, S., Salm, R., Bjork, M., Duarte, C., … Silliman, B. (2011). A blueprint for blue carbon: toward an improved understanding of the role of vegatated coastal habitats in sequestering CO2. Frontiers in Ecology and the Environment, 9, 552-560.,Collins, M.J. (1986). Taphonomic processes in a deep water Modiolus-brachiopod assemblage from the west coast of Scotland. Retrieved from https://core.ac.uk/download/pdf/211234226.pdf [accessed 21 February 2021],Migne, A., Davoult, D., & Gattuso, J.P. (1998). Calcium carbonate production of a dense population of the brittle star Ophiothrix fragilis (Echinodermata: Ophiuroidea): role in the carbon cycle of a temperate coastal ecosystem. Marine Ecology Progress Series, 173, 305-308.,Lee, H.Z.L., Davies, I.M., Baxter, J.M., Diele, K., & Sanderson, W.G. (2020). Missing the full story: First estimates of carbon deposition rates for the European flat oyster, Ostrea edulis. Aquatic Conservation, 30, 2076-2086.. Terrestrial data replotted from Scottish Forestry . (2020). Climate Mitigation: Woodland creation and management. Retrieved from https://forestry.gov.scot/publications/973-information-note-climate-mitigation-woodland-creation-and-management/viewdocument,Artz, R.R.E., Chapman, S.J., Donnelly, D., & Matthews, R.B. (2011). Potential Abatement from Peatland Restoration. Retrieved from https://www.climatexchange.org.uk/media/1501/research_summary_potential_abatement_from_peatland_restoration.pdf [accessed 17 February 2021],Clymo , R.S., Turunen , J., & Tolonen, K. (1998). Carbon Accumulation in Peatland. Oikos, 81, 368-388.

National Marine Plan

The Marine (Scotland) Act 2010 and Marine and Coastal Access Act 2009 (collectively referred to as the Marine Acts) require Scottish Ministers to prepare and adopt a National Marine Plan (NMP), which must provide:

• An assessment of the condition of the Scottish marine area or, as the case may be, Scottish marine region at the time of the plan's preparation

• A summary of significant pressures and the impact of human activity on the area or region.

The most recent assessment is The Scotland Marine Assessment 2020, which provides the scientific basis to inform the 2021 review of the NMP. The Marine Assessment represents a cooperative effort between Marine Scotland, SEPA, NatureScot, Crown Estate Scotland and others.

Regional Marine Assessments

Regional Marine Assessments provide a more localised assessment of the marine environment to inform Marine Management Schemes (outlined in further detail under MPA management) and are a requirement of Section 5 of the Marine (Scotland) Act 2009. Examples include the Clyde Region Marine Assessment and the Shetland Islands Marine Region State of the Environment.

Other Assessment measures

Ongoing assessment of the health of (some) blue carbon habitats is additionally provided by the OSPAR commission, The Dynamic Coast National Coastal Change Assessment and the Biodiversity Duty.

The OSPAR Commission

The OSPAR Commission is an inter-governmental body responsible for overseeing the 1992 Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention) - to which the UK is a party. The OSPAR Commission carries out an assessment of the broader North-East Atlantic marine region. The latest assessment product (OSPAR 2017 Intermediate Assessment) outlines the biodiversity status and pressures from human activities and climate change in the North Atlantic OSPAR regions.

To meet its commitment of identifying species and habitats in need of protection, the OSPAR Commission developed the List of Threatened and/or Declining Species and Habitats. These species and habitats are a priority for the work of the Commission.

The list reports that seagrass, biogenic reefs, and maerl beds are under threat in all areas across the wider North-East Atlantic area, including in Scottish seas. The list additionally reports that seagrasses are under decline in the North Sea. The OSPAR Commission outlines that human activities are causing damage to habitats like maerl beds¹OSPAR Commission. (2008). Case Reports for the OSPAR List of Threatened and/or Declining Species and Habitats: Maerl Beds. Retrieved from <a href="https://www.ospar.org/site/assets/files/1892/maerl_beds.pdf" target="_blank">https://www.ospar.org/site/assets/files/1892/maerl_beds.pdf</a> [accessed 21 February 2021].

The Dynamic Coast National Coastal Change Assessment

The Scottish Government commissioned The National Coastal Change Assessment to deliver an assessment of coastal changes in support of Scotland's Climate Change Adaptation Programme (A requirement of the Climate Change Acts). The work was undertaken by Dynamic Coast and supported by other key agencies. The assessment summarised the last 130 years of coastal change across all of Scotland’s erodible shores (i.e. coastal environments) and projected the changes forward to 2050.

Biodiversity Duty

As outlined in Section 2A of the Conservation (Scotland) Act 2004, every public body in Scotland is required to produce a publicly available report on compliance with the Biodiversity duty. The report must contain details of actions to increase understanding of human impacts on biodiversity.

The key threats to and pressures on biological and geological blue carbon stores are those associated with:

1. Physical disturbance to habitats arising from:

   1. Fishing activities (e.g. bottom trawling, dredging, deployment of moorings)

   2. Recreational boating and shipping (e.g. anchors)

   3. Installation of infrastructure (e.g. installation of renewable energy platforms, cable laying)

   4. Aquaculture (e.g. Mechanical harvesting)

2. Changes in land management and land-use change

   1. Coastal land-use change and reclamation for development activities (infrastructure, industrial, recreational, agriculture, and tourism)

   2. Groundwater drainage

   3. Human developments (e.g. flood defences which prevent coastal habitats from migrating landward as sea level rises)

   4. Pollution

3. Climate change, which is associated with a range of environmental changes, including:

   1. Ocean Acidification (decrease in ocean pH)

   2. Ocean warming

   3. Deoxygenation (a loss of oxygen from the ocean)

   4. Sea-level rise

   5. Increased storminess (increased wave energy).

These pressures can change the suitability of the marine environment for biological species and ecosystems, and therefore impact their ability to sequester and store carbon. Studies examining the current and future effect of climate change on Scottish marine ecosystems are ongoing.

Geological Carbon Stores

Aside from their impacts on biodiversity, human activities such as bottom-towed fishing can physically disturb seafloor sediments¹Lindboom , H.J., &amp; de Groot, S.J. (1998). The effects of different types of fisheries on the North Sea and Irish Sea benthic invertebrates. Netherlands Institute of Sea Fisheries, Texel.²O'Neill, F.G., &amp; Ivanovic, A. (2016). The physical impact of towed demersal fishing gears on soft sediments . ICES Journal of Marine Science, 73, 5-14..

The effect of physical disturbance on sediment carbon release remains an area of ongoing research. Physical disturbance to sediments can release stored carbon back into the water column and has been demonstrated in North Sea sediments³van de Velde, S., Van Lancker, V., Hidalgo-Martinez, S., Berelson, W.M., &amp; Meysman, F.J. (2018). Anthropogenic disturbance keeps the coastal seafloor biogeochemistry in a transient state. Scientific Reports, 8, 1-10.. The impact of physical disturbance intensity remains unclear but holds implications for determining whether the majority of carbon release occurs from single incidences or repeated disturbance through human activities.

Research shows that organic carbon density varies over Scotland's seas⁴Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science., suggesting that the effect of physical disturbance on carbon release depends on location⁵Tillin , H.M., Hull, S.C., &amp; Tyler-Walters, H. (2010). Development of a Sensitivity Matrix (pressures-MCZ/MPA features). Report to the Department of Environment, Food and Rural Affairs from ABPMer, Southampton and the Marine Life Information Network (MarLIN) Plymouth: Marine Biological Association of the UK. .Defra Contract No. MB0102 Task 3A, Report No. 22.. Retrieved from <a href="http://plymsea.ac.uk/id/eprint/7030/1/MB0102_9721_TRP%20(14)%20(1).pdf" target="_blank">http://plymsea.ac.uk/id/eprint/7030/1/MB0102_9721_TRP%20(14)%20(1).pdf</a> [accessed 13 February 2021]. Sea loch sediments and inshore seafloor sediment have high organic carbon densities⁴Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.⁷Hunt, C., Demsar, U., Dove, D., Smeaton, C., Cooper, R., &amp; Austin, W.E.N. (2020). Quantifying Marine Sedimentary Carbon: A New Spatial Analysis Approach Using Seafloor Acoustics, Imagery, and Ground-Truthing Data in Scotland. Frontiers in Marine Science , 7., and as such may be more sensitive to carbon release following physical disturbance - however this is an ongoing area of research.

Biological blue carbon species and habitats

Some human activities physically impact biological blue carbon species and habitats, including:

• Bottom-towed fishing activities

• Large-scale mechanised kelp harvesting, whereby the whole kelp plant is removed and prevents kelp regrowth⁸SIFT. (2018). Protection for Scotland’s kelp forests. Retrieved from <a href="https://www.sift.scot/wp-content/uploads/2019/01/SIFT-Kelp-Briefing.pdf" target="_blank">https://www.sift.scot/wp-content/uploads/2019/01/SIFT-Kelp-Briefing.pdf</a> [accessed 12 February 2021]. There are restrictions on the mechanical removal of kelp for commercial use as part of the Scottish Crown Estate Act 2019.

• Cable deployment and maintenance can also cause some physical damage to seabed habitats, but this disruption is minimal⁹United Nations Environment Programme . (2009). Submarine cables and the oceans: connecting the world. Retrieved from <a href="https://www.iscpc.org/documents/?id=132" target="_blank">https://www.iscpc.org/documents/?id=132</a> [accessed 12 February 2021].

• Boating and anchoring activities in seagrass meadows may kill seagrasses and diminish the underlying soil's carbon-storing capacity¹⁰Collins, K.J., Suonpää, A.M., &amp; Mallinson, J.J. (2010). The impacts of anchoring and mooring in seagrass, Studland Bay, Dorset, UK. Underwater Technology , 29, 117-123.¹¹European Commission. (2015). Protecting seagrass from anchor damage: new recommendations. Retrieved from <a href="https://ec.europa.eu/environment/integration/research/newsalert/pdf/new_recommendations_for_protecting_seagrass_against_anchor_damage_411na3_en.pdf" target="_blank">https://ec.europa.eu/environment/integration/research/newsalert/pdf/new_recommendations_for_protecting_seagrass_against_anchor_damage_411na3_en.pdf</a> [accessed 15 February 2021].

Ⓒ Fisker Forum

Bottom trawling is a fishing method that involves dragging a net along the seafloor to catch fish such as pollock, cod, flounder and prawns. Dredging involves dragging a heavy frame with an attached mesh bag along the seafloor to catch animals living on or in the mud or sand; catches include scallops, clams and oysters.

© seafish.org

Bottom trawling and dredging is one of the main causes of seabed disturbance in the UK's seas and globally¹Dunkley , F., &amp; Solandt, J. (2021). Marine unProtected Areas: A case for a just transition to ban bottom trawl and dredge fishing in offshore Marine Protected Areas. Retrieved from <a href="https://www.mcsuk.org/media/marine-unprotected-areas-full-report.pdf" target="_blank">https://www.mcsuk.org/media/marine-unprotected-areas-full-report.pdf</a> [accessed 12 February 2021]²Paradis, S., Goni, M., Masque, P., Duran, R., Arjona-Camas, M., Palanques, A., … Puig, P. (2021). Persistence of Biogeochemical Alterations of Deep‐Sea Sediments by Bottom Trawling. Geophysical Research Letters, 48.. Scotland's Marine Assessment 2020 concluded that disturbance caused by towed, bottom-contacting fishing was widespread across most Scottish Marine Regions and Offshore Marine regions. The analysis considered disturbance from surface and sub-surface abrasion caused by fishing vessels over 12 m in length using Vessel Monitoring System (VMS) (reporting vessels) fishing with bottom contacting gears. The analysis predicted that seafloor habitats are in poor condition across more than half of their area in nine out of 21 Scottish Marine regions, and some level of damage is likely in all regions.

Ⓒ Marine Scotland (Scottish Marine Assessment)

Management of bottom-towed fishing

The designation of an MPA does not automatically introduce fisheries restrictions⁴Harrison, J. (2019). Saving our Seas through Law Briefing No. 4 - Legal Tools for the Management of Marine Protected Areas in Scotland. Edinburgh Law School.. However, a number of restrictions on fishing in MPAs have been established to avoid threats to protected features. Fishing in MPAs can be regulated using powers under the Inshore Fishing (Scotland) Act 1984, which allows Scottish Ministers to prohibit fishing within particular areas or through introduction of a Marine Conservation Order under the Marine (Scotland) Act 2010. Currently, 2.5% of regions found within MPAs are subject to management measures that restrict or ban mobile bottom-towed fishing⁵Langton, R., Stirling, D., Boulcott, P., &amp; Wright, P.J. (2020). Are MPAs effective in removing fishing pressure from benthic species and habitats?. Biological Conservation, 247..

Data (replotted) Ⓒ Marine Scotland

Geological Blue Carbon Stores

The effect of bottom-towed fishing on carbon release from sediments remains an ongoing research area. Initial estimates predict that a single trawl pass releases 0.07 tonnes of CO2-eq per hectare⁶Luisetti, T., Turner, R.K., Andrews, J.E., Jickells, T.D., Kroger, S., Diesing, M., … Weston, K. (2019). Quantifying and valuing carbon flows and stores in coastal and shelf ecosystems in the UK. Ecosystem services, 35, 67-76.. As with all physical disturbances, the quantity of carbon release will depend on the sediment type and carbon density.

A recent study estimates that 90% of the UK's Exclusive Economic Zone is within the top 10% of the global ocean that should be safeguarded through MPA networks for it's sediment carbon stores⁷Sala, E., Mayorga, J., Bradley, D., Cabral, R., Atwood, T., Auber, A., … Lubchenco, J. (2021). Protecting the global ocean for biodiversity, food and climate. Nature. doi: https://doi.org/10.1038/s41586-021-03371-z. Currently, only a small proportion of Scotland's seafloor sediment organic carbon stores are within regions where bottom-trawling or dredging activities are restricted or banned completely. Scottish Ministers have powers to manage marine geological carbon stores as part of Marine Protected Areas, in recognition of their role in mitigating climate change.

Organic carbon data replotted from Smeaton, C., Hunt, C.A., Turrell, W., & Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.

Marine Biological Carbon Stores

The physical disturbance caused by bottom-towed fishing, notably scallop dredging has detrimental impacts on kelp, biogenic reefs and seagrass communities in Scottish waters⁹Kaiser, M.J., Clarke , K.R., Hinz , H., Austen, M.C.V., Somerfield, P.J., &amp; Karakassis, I. (2006). Global analysis of response and recovery of benthic biota to fishing. Marine Ecology Progress Series, 311, 1-14.¹⁰Stirling, D.A., Boulcott, P., Scott, B.E., &amp; Wright, P.J. (2016). Using verified species distribution models to inform the conservation of a rare marine species. Diversity and Distributions, 22, 808-822.. A single dredge-tow can remove up to 70% of maerl and entire flame-shell beds¹¹Hall-Spencer, J.M., &amp; Moore, P.G. (2000). Scallop dredging has profound, long-term impacts on maerl habitats. ICES Journal of marine science, 57, 1407-1415., taking decades to recover¹²Trigg, C., &amp; Moore, C.G. (2009). Recovery of the biogenic nest habitat of Limaria hians (Mollusca: Limacea) following anthropogenic disturbance. Estuarine, Coastal and Shelf Science, 82, 351-356. and releasing the carbon associated with these deposits¹³Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. Maerl beds have declined across the west coast of Scotland in response to the expansion of the scallop industry¹¹Hall-Spencer, J.M., &amp; Moore, P.G. (2000). Scallop dredging has profound, long-term impacts on maerl habitats. ICES Journal of marine science, 57, 1407-1415.¹⁵Hall-Spencer, J.M., Grall, J., Moore, P.G., &amp; Atkinson, R.J.A. (2003). Bivalve fishing and maerl‐bed conservation in France and the UK—retrospect and prospect. Aquatic Conservation: Marine and Freshwater Ecosystems, 13, 33-41..

Currently, a small proportion of Scotland's blue carbon habitats (within the Priority Marine Features list) lie within regions where bottom-towed fishing activities are banned or restricted. In April 2017, a flame shell bed was damaged in Loch Carron by illegal scallop dredging activity. In response, the Scottish Government began a scoping project to improve protection given to Priority Marine Features (PMFs) outside Marine Protected Areas.

The project identified 11 habitats which are particularly sensitive to impact from bottom contacting mobile fishing gears, of which the following are blue carbon habitats:

• Blue mussel beds

• Cold-water coral reefs

• Flame shell beds

• Horse mussel beds

• Maerl beds

• Maerl or coarse shell gravel with burrowing sea cucumbers

• Seagrass beds

• Serpulid aggregations

Priority Marine Features data replotted from Geodatabase of Marine features adjacent to Scotland (GeMS) (V9i25) © NatureScot and JNCC

Geological Carbon Stores

Ocean acidification is a particular threat to marine organisms which produce shells or external skeletons formed of inorganic carbon (e.g. Biogenic reefs and some phytoplankton). A change in marine organisms' ability to produce inorganic carbon shells or external skeletons may indirectly impact the amount of inorganic carbon delivered to seafloor and sea loch sediments for long-term carbon storage.

Ocean acidification may also directly increase inorganic carbon dissolution in already buried sediments¹Doney, S.C., Fabry, V.J., Feely, R.A., &amp; Kleypas, J.A. (2009). Ocean acidification: the other CO2 problem. Annual review of marine science, 15, 169-192., releasing stored inorganic carbon. However, as sites monitoring Scottish seawater chemistry have less than 20 years of data²Marine Scotland. (2020). Scotland's Marine Assessment: Ocean Acidification. Retrieved from <a href="http://marine.gov.scot/sma/assessment/ocean-acidification" target="_blank">http://marine.gov.scot/sma/assessment/ocean-acidification</a> [accessed 13 February 2021], it is not possible to accurately determine whether there has been a significant change in oceanic pH and carbonate chemistry to cause such effects in Scottish waters.

Biological Carbon Stores

Under all projected ocean acidification scenarios, ideal conditions for organisms which produce shells or external skeletons (such as maerl beds, cold-water corals and flame shell beds) are predicted to decrease in extent³Simon-Nutbrown, C., Hollingsworth, P.M., Fernandes, T.F., Kamphausen, L., Baxter, J.M., &amp; Burdett, H.L. (2020). Species Distribution Modeling Predicts Significant Declines in Coralline Algae Populations Under Projected Climate Change With Implications for Conservation Policy. Frontiers in Marine Science , 7.⁴Gormley, K.S., Porter, J.S., Bell, M.C., Hull, A.D., &amp; Sanderson, W.G. (2013). Predictive habitat modelling as a tool to assess the change in distribution and extent of an OSPAR priority habitat under an increased ocean temperature scenario: consequences for marine protected area networks and management. PloS one, 8.. Cold-water corals found in deep waters, such as the Darwin Mounds to the northeast of Rockall and the Mingulay reef complex in the Sea of the Hebrides, are particularly sensitive to ocean acidification⁵Findlay, H., Artioli, Y., Navas, J., Hennige, S., Wicks, L., Huvenne, V., … Roberts, M. (2013). Tidal downwelling and implications for the carbon biogeochemistry of cold-water corals in relation to future ocean acidification and warming. Global Change Biology, 19, 2708-2719.. Ocean acidification has also been shown to decrease the strength of mussel attachment⁶Zhao, X., Guo, C., Han, Y., Che, Z., Wang, Y., Wang, X., … Liu, G. (2017). Ocean acidification decreases mussel byssal attachment strength and induces molecular byssal responses. Marine Ecology Progress Series, 565, 67-77., with implications for the ability of mussels to form biogenic reefs. Depending on the rate of ocean acidification, there is some evidence that organisms may adapt to increasing acidification⁷Marine Climate Change Impacts Partnership . (2018). Maerl beds. Retrieved from <a href="http://www.mccip.org.uk/climate-smart-adaptation/climate-change-and-marine-conservation/" target="_blank">http://www.mccip.org.uk/climate-smart-adaptation/climate-change-and-marine-conservation/</a> [accessed 12 February 2021]¹Doney, S.C., Fabry, V.J., Feely, R.A., &amp; Kleypas, J.A. (2009). Ocean acidification: the other CO2 problem. Annual review of marine science, 15, 169-192. but this would only apply to living organisms (e.g. living maerl) and not dead inorganic carbon stores such as maerl beds.

Geological Carbon stores

As the ocean warms, its ability to store oxygen decreases, leading to oxygen loss (deoxygenation). Oxygen is required for the breakdown and release of carbon from phytoplankton and kelp biomass. A reduction in oxygen concentrations may therefore promote the preservation of phytoplankton and kelp-derived carbon into seafloor and sea loch sediments. Sea lochs are already prone to undergoing periods of low oxygen, potentially explaining their relatively greater organic carbon burial¹Gillibrand, P.A., Cromey, C.J., Black, K.D., Inall, M.E., &amp; Gontarek, S.J. (2006). Identifying the risk of deoxygenation in Scottish sea lochs with isolated deep water. Scottish Aquaculture Research Forum, SARF, 7.. Oxygen levels can vary at different depths²Queste , B.Y., Fernand, L., Jickells, T.D., &amp; Heywood, K.J. (2013). Spatial extent and historical context of North Sea oxygen depletion in August 2010. Biogeochemistry, 113, 53-68., and the Scottish Marine Assessment 2020 reports there is currently insufficient data to make a robust assessment for near-bed oxygen levels. Therefore the potential for ocean deoxygenation to impact carbon burial in sediments remains unclear.

Biological Carbon Stores

The effect of ocean deoxygenation on blue carbon ecosystems is variable, as the concentration of oxygen required to invoke a toxic effect is species-specific³Vaquer-Sunyer, R., &amp; Duarte, C.M. (2008). Thresholds of hypoxia for marine biodiversity. PNAS, 105, 15452-15457.. Deoxygenation is predicted to negatively impact maerl species richness⁴Marine Life Information Network. (2018). Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand. Retrieved from <a href="https://www.marlin.ac.uk/habitats/detail/64" target="_blank">https://www.marlin.ac.uk/habitats/detail/64</a> [accessed 14 February 2021], and oxygen depletion will kill living maerl⁵Marine Scotland. (2013). FEAST - Feature Activity Sensitivity Tool. Retrieved from <a href="https://www.marine.scotland.gov.uk/feast/Index.aspx" target="_blank">https://www.marine.scotland.gov.uk/feast/Index.aspx</a> [accessed 13 February 2021] and hamper kelp growth⁶Crowder, L.B., Ng, C.A., Frawley, T.H., Low, N.H.N., &amp; Micheli, F. (2019). The significance of ocean deoxygenation for kelp and other macroalgae in Ocean deoxygenation: everyone's problem. Retrieved from <a href="https://portals.iucn.org/library/sites/library/files/documents/08.3%20DEOX.pdf" target="_blank">https://portals.iucn.org/library/sites/library/files/documents/08.3%20DEOX.pdf</a> [accessed 13 February 2021]. Historical data over the last century from the International Council for the Exploration of the Sea oceanographic database highlight an increase in seasonal oxygen depletion that is considered low enough to cause detrimental, and potentially lethal, effects on marine ecosystems⁷Diaz, R.J., &amp; Rosenberg, R. (2008). Spreading dead zones and consequences for marine ecosystems. Science , 321, 926-929..

Biological carbon habitats

There is evidence that coastal habitats in Scotland are already experiencing the effects of increased temperatures and sea-level rise¹Scottish Government. (2011). Scotland's Marine Atlas: Information for The National Marine Plan: TEMPERATURE, SALINITY AND OCEAN ACIDIFICATION. Retrieved from <a href="https://www.gov.scot/publications/scotlands-marine-atlas-information-national-marine-plan/pages/9/" target="_blank">https://www.gov.scot/publications/scotlands-marine-atlas-information-national-marine-plan/pages/9/</a> [accessed 20 February 2021]²Burden, A., Smeaton, C., Angus, S., Garbutt, A., Jones, L., Lewis, H., … Rees, S. (2020). Impacts of climate change on coastal habitats, relevant to the coastal and marine environment around the UK. MCCIP Science Review 2020.. Increased sea temperatures can reduce the growth of seagrasses³Short, F.T., Polidoro, B., Livingstone, S.R., Carpenter, K.E., Bandeira, S., Bujang, J.S., … Erftemeijer, P.L. (2011). Extinction risk assessment of the world’s seagrass species. Biological Conservation, 144, 1961-1971., maerl⁴Martin, S., &amp; Hall-Spencer, J.M. (2017). Effects of ocean warming and acidification on rhodolith/maërl beds. In Rhodolith/maërl beds: A global perspective. Cham: Springer. and kelp forests⁵Smale, D. (2020). Impacts of ocean warming on kelp forest ecosystems. New Phytologist, 225, 1447-1454.. In some cases, particularly for kelp, the effect of rising temperatures is uncertain due to sparse data coverage, inconsistent methodology and lack of adequate temperature time-series. Nonetheless, ocean warming has decreased the prevalence of the UK kelp species, Saccorhiza polyschides⁶Fernández, C. (2011). The retreat of large brown seaweeds on the north coast of Spain: the case of Saccorhiza polyschides. European Journal of Phycology, 46, 352-360.. In addition, ocean warming may shift the dominant species composition of kelp⁵Smale, D. (2020). Impacts of ocean warming on kelp forest ecosystems. New Phytologist, 225, 1447-1454., with potential implications for carbon sequestration rates. A change to the dominant species of phytoplankton has already been identified in the North-east Atlantic area of Scotland's seas by the Continuous Plankton Recorder (CPR). Research is ongoing to identify the factors which drive the change in phytoplankton species in Scotland's marine environment.

Sea-level rise is a particular threat to low-lying coastal habitats such as saltmarshes, machair and sand dunes. Research predicts that sea-level rise will reduce saltmarsh and machair area by 6% by 2060⁸Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., &amp; Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40.. Other climate-change driven changes, such as changes in rainfall patterns, are expected to have a detrimental effect on sand dune habitats. There has been a 30% decrease in dune slack (low-lying dune areas) extent at certain sites in England, ostensibly due to drying out²Burden, A., Smeaton, C., Angus, S., Garbutt, A., Jones, L., Lewis, H., … Rees, S. (2020). Impacts of climate change on coastal habitats, relevant to the coastal and marine environment around the UK. MCCIP Science Review 2020..

Land Use Change

Land-use change for human activities is a threat to coastal blue carbon habitats such as saltmarshes, sand dunes and machair. The main threats are land claim for agricultural crop production and grazing livestock, water diversion through dams, dykes and canals, and pollution from both air and water-borne sources. Around the UK, saltmarsh habitat losses have occurred due to drainage and reclamation for agriculture or other coastal development¹Morris, R., Reach, I., Duffy, M., Collins, T., &amp; Leafe, R. (2004). On the loss of saltmarshes in south-eas England and the relationship with Nereis diversicolor. Journal of Applied Ecology, 41.. In Scotland, large areas of saltmarsh were claimed for agriculture in the past, notably in the Firth of Forth.

Other human developments, such as the installation of coastal defences, can also negatively impact saltmarshes. Providing sediment supply is high, saltmarshes can keep pace with sea-level rise, moving landwards and acting as a natural coastal management strategy. If artificial flood defences, such as sea walls, are present, saltmarshes are prevented from migrating landward naturally, causing them to decrease in size in a process known as 'coastal squeeze'²Burden, A., Smeaton, C., Angus, S., Garbutt, A., Jones, L., Lewis, H., … Rees, S. (2020). Impacts of climate change on coastal habitats, relevant to the coastal and marine environment around the UK. MCCIP Science Review 2020.. Coastal erosion can also negatively impact sand dunes, which are expected to decrease 6% by 2060³Beaumont, N.J., Jones, L., Garbutt, A., Hansom, J.D., &amp; Toberman, M. (2014). The value of carbon sequestration and storage in coastal habitats. Estuarine, Coastal and Shelf Science, 137, 32-40..

Increased sediment supply

Land reclamation (land gain from the sea or coastal wetlands for agricultural purposes, industrial use or port expansions) may deposit more sediment into nearby coastal waters. This can lead to decreased seawater clarity, which reduces light availability and therefore marine organisms' ability to carry out photosynthesis and sequester carbon. Maerl beds in the British Isles are already restricted to shallow waters, and therefore changes in light availability may adversely affect the depth distribution of maerl⁴Marine Scotland. (2013). FEAST - Feature Activity Sensitivity Tool. Retrieved from <a href="https://www.marine.scotland.gov.uk/feast/Index.aspx" target="_blank">https://www.marine.scotland.gov.uk/feast/Index.aspx</a> [accessed 13 February 2021]. A reduction in light can also lead to seagrass mortality⁵van Lent, F., Verschuure, J.M., &amp; van Veghel, M.L. (1995). Comparative study on populations of Zostera marina L.(eelgrass): in situ nitrogen enrichment and light manipulation. Journal of Experimental Marine Biology and Ecology, 185, 55-76. with coastal engineering and dredging implicated in the decline of seagrass beds worldwide⁶Fraser, M.W., &amp; Kendrick, G.A. (2017). Belowground stressors and long-term seagrass declines in a historically degraded seagrass ecosystem after improved water quality. Scientific Reports, 7, 14469.⁷Davison, D.M., &amp; Hughes, D.J. (1998). Zostera Biotopes (volume I). An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Science (UK Marine SACs Project).. Climate change-related storm events, which deliver high sediment loads to coastal environments, can also lead to similar effects and result in seagrass mortality⁸Preen, A., &amp; Marsh, H. (1995). Response of dugongs to large-scale loss of seagrass from Hervey Bay, Queensland Australia . Wildlife Research, 22, 507..

Overview

Some blue carbon habitats are protected by current legislation, based on their contributions to Scotland's biodiversity. However, there are opportunities for blue carbon habitats and stores to be protected given their role in climate change mitigation.

Legal protection of blue carbon habitats and species (based on biodiversity contributions) is underpinned by powers made available to Scottish Ministers through the Marine (Scotland) Act 2010 and Marine and Coastal Access Act 2009 (referred to as the Marine Acts). Some blue carbon habitats are afforded legal protection through the Nature Conservation (Scotland) Act 2004 (Sites of Special Scientific Interest), Conservation (Natural Habitats,&c.) Regulations 1994 (Special Areas of Conservation) and the Scottish Crown Estate Act.

Marine (Scotland) Act 2010 is an Act of Scottish Parliament which gives Scottish Ministers powers over Scotland's Territorial waters (waters up to 12 nautical miles off the coastline, known as the Inshore Zone). The Marine and Coastal Access Act 2009 is an Act of the UK Parliament that gives Scottish Ministers power over Scottish offshore waters (the Exclusive Economic Zone and continental shelf). Collectively, these are termed the Marine Acts.

General principles

On a broad level, Section 3 and 4 of the Marine (Scotland) Act 2010 require that when exercising powers under the Act, Scottish Ministers and other public authorities must (emphasis added):

act in the way best calculated to further the achievement of sustainable development, including the protection and, where appropriate, enhancement of the health of that area, so far as is consistent with the proper exercise of that function

and -

act in the way best calculated to mitigate, and adapt to, climate change so far as is consistent with the purpose of the function concerned.

More specific opportunities for blue carbon protection fall under the setting out and implementation of a National Marine Plan and Nature Conservation Marine Protected Areas.

Under the Marine Acts, Scottish Ministers must prepare and adopt a National Marine Plan (NMP) which must set:

1. Economic, social and marine ecosystem objectives,

2. Objectives relating to the mitigation of, and adaptation to, climate change

And must prepare (as outlined in Assessment of Scotland's Blue Carbon):

1. An assessment of the condition of the Scottish marine area or, as the case may be, Scottish marine region at the time of the plan's preparation

2. Summary of significant pressures and the impact of human activity on the area or region.

The Plan may also 'include statements or information relating to policies'.

NMP and Priority Marine Features

The current NMP (published in 2015) sets out policies that aim to enable the sustainable development of Scotland’s marine resources out to 200 nautical miles, framed under a set of general policies that apply across all existing and future development and use of the marine environment.

General Policy number 9 in the NMP is relevant to blue carbon habitats, and states that the development and use of the marine environment must (emphasis added):

• Comply with legal requirements for protected areas and protected species.

• Not result in significant impact on the national status of Priority Marine Features.

• Protect and, where appropriate, enhance the health of the marine area.

The Marine Acts (Section 15 of the Marine (Scotland) Act 2010; Section 58 of the Marine and Coastal Access Act 2009) require that public authorities take authorisation or enforcement decisions in accordance with the NMP (and policies therein) and have regard to the NMP in taking other decisions if they impact on the marine area.

Public authorities must therefore make decisions with regard to, among other things, General Policy Number 9 of the NMP and their impact on the national status of Priority Marine Features (which includes some blue carbon habitats). The NMP elaborates on this:

Development and use of the marine environment must not result in significant impact on the national status of Priority Marine Features. Impacts of development and use on the national status of Priority Marine Features must be considered when decisions are being made, taking account of the advice of Statutory Advisors. Where planned developments or use have potential to impact PMFs, mitigation, including alternative locations, should be considered. Actions should be taken to enhance the status of PMFs where appropriate.

Marine protected areas (MPAs) play a key role in protecting Scotland's biodiversity and help Scotland achieve its international commitments towards enhancing biodiversity.

For instance, both the UN Sustainable Development Goals and the Convention on Biological Diversity (Aichi Targets) set targets for increasing the percentage of the oceans protected through MPAs. The Aichi target further outlines that these regions 'are conserved through effectively and equitably managed, ecologically representative and well -connected systems of protected areas'.

Once MPAs have been designated, their ability to meet biodiversity goals relies on effective MPA management.

Data (replotted) from Ⓒ Nature Scot

The Marine Acts include powers for Scottish Ministers to designate Nature Conservation MPAs, based on:

1. Conserving flora or fauna

2. Conserving marine habitats or types of such habitat

3. Conserving features of geological or geomorphological interest

The designation of Nature Conservation MPAs is based on a sub-list (known as MPA search features) of Priority Marine Features (PMFs). Priority Marine Features are a list of habitats of conservation priority including numerous blue carbon habitats such as kelp beds, seagrasses and biogenic reefs¹Nature Scot . (2016). Descriptions of Scottish Priority Marine Features (PMFs) . Retrieved from <a href="https://www.nature.scot/sites/default/files/Publication%202016%20-%20SNH%20Commissioned%20Report%20406%20-%20Descriptions%20of%20Scottish%20Priority%20Marine%20Features%20%28PMFs%29.pdf" target="_blank">https://www.nature.scot/sites/default/files/Publication%202016%20-%20SNH%20Commissioned%20Report%20406%20-%20Descriptions%20of%20Scottish%20Priority%20Marine%20Features%20%28PMFs%29.pdf</a>²Scottish Government . (2017). Guidelines for Selecting &amp; Developing MPAs. Retrieved from <a href="https://www.webarchive.org.uk/wayback/archive/3000/https://www.gov.scot/Resource/0051/00515466.pdf" target="_blank">https://www.webarchive.org.uk/wayback/archive/3000/https://www.gov.scot/Resource/0051/00515466.pdf</a>³Carruthers, M., Chaniotis, P.D., Clark, L., Crawford-Avis, O., Gillham, K., Linwood, M., … Wilson, E. (2011). Contribution of existing protected areas to the MPA network and identification of remaining MPA search feature priorities. Internal report produced by Scottish Natural Heritage, the Joint Nature Conservation Committee and Marine Scotland for the Scottish Marine Protected Areas Project.⁴Scottish Natural Heritage and the Joint Nature Conservation Committee. (2012). Advice to the Scottish Government on the selection of Nature Conservation Marine Protected Areas (MPAs) for the development of the Scottish MPA network. Scottish Natural Heritage Commissioned Report No. 547.. Excluding kelp beds, all blue carbon habitats which are PMFs are also MPA search features:

• Biogenic Reefs

  • Horse mussel beds (biogenic reefs)

  • Fan mussel aggregations

  • Native oysters

  • Maerl and Maerl beds

  • Flame Shell Beds

  • Coral gardens

  • Blue mussel beds

• Seagrass beds

• Kelp on sublittoral sediments

Special Areas of Conservation (SACs)

A Special Area of Conservation (SAC) protects one or more special habitats and/or species, listed in the Habitats Directive, receiving protection under the Conservation (Natural Habitats, &c.) Regulations 1994. Currently, SAC designations for blue carbon protection include biogenic reef-forming habitats, sand dunes and machair⁵Nature Scot. (2019). Habitats (listed on Annex I) and species (listed on Annex II) of the Habitats Directive which occur in Scotland and for which Special Areas of Conservation are selected. Retrieved from <a href="https://www.nature.scot/sites/default/files/2019-02/Common%20names%20for%20Annex%20I%20habitats%20and%20Annex%20II%20species.pdf" target="_blank">https://www.nature.scot/sites/default/files/2019-02/Common%20names%20for%20Annex%20I%20habitats%20and%20Annex%20II%20species.pdf</a>(most notably Monach Isles SAC and South Uist SAC⁶Burrows, M.T., Hughes, D.J., Austin, W.E.N., Smeaton, C., Hicks, N., Howe, J.A., … Vare, L.L. (2017). Assessment of Blue Carbon Resources in Scotland’s Inshore Marine Protected Area Network. Scottish Natural Heritage Commissioned Report No. 957.).

Together, SACs and Nature Conservation MPAs make up the majority of Scotland's marine protected network. MPA and SAC management aims to conserve the features on which the MPA has been designated, support the restoration of identified features, and restrict activities that prevent these goals from being reached.

Data (replotted) from Ⓒ Nature Scot

Once designated, MPAs can be managed in a variety of means to restrict activities that harm designated MPA features. The role of Nature Conservation MPAs is to ensure that protected features 'so far as already in favourable condition, remain in such condition, and so far as not already in favourable condition, be brought into such condition, and remain in such condition' ¹Scottish Government. (2020). The North-east Lewis Nature Conservation Marine Protected Area Order 2020. Retrieved from <a href="https://consult.gov.scot/marine-conservation/smallislesdoconsultation2016/supporting_documents/Small%20Isles%20DO%202014.pdf" target="_blank">https://consult.gov.scot/marine-conservation/smallislesdoconsultation2016/supporting_documents/Small%20Isles%20DO%202014.pdf</a> [accessed 21 February 2021].

MPA status does not automatically introduce restrictions on human activities, such as restrictions on bottom-towed fishing. However, activities proposed in the protected area must be shown to have benefits that outweigh the risk of damage. If an authority believes that an activity poses a significant risk to the conservation objectives of an MPA, it is required to notify the Scottish Ministers and NatureScot, and wait 28 days before granting authorisation. Section 95 of the Marine Scotland Act 2010 makes it a criminal offence for a person to intentionally or recklessly carry out a prohibited act (including damaging or destroying any protected habitat or feature of the MPA) in an MPA.

Marine Management Schemes

Under Section 99 of the Marine (Scotland) Act 2010 Scottish Ministers and any public authority exercising functions in a Scottish MPA, can establish a Marine Management Scheme. These schemes aim to fulfil functions such as:

• Explaining the conservation objectives for the site

• Identifying key threats to the designated features

• Listing the actions that should be taken

• Setting out how progress will be monitored

The purpose of Marine Management Schemes is to provide a more spatially-tailored management approach which can assess the precise threats posed by activities and be more readily responsive to new information as it comes to light³Harrison, J. (2019). Saving our Seas through Law Briefing No. 4 - Legal Tools for the Management of Marine Protected Areas in Scotland. Edinburgh Law School.. However, no marine management schemes have been adopted to date.

Marine Conservation Orders

Under Section 85 of the Marine (Scotland) Act 2010, Scottish Ministers can make Marine Conservation Orders (MCOs) that regulate, restrict or prohibit particular activities to further the conservation objectives of the MPA. These are only recommended where existing measures of regulation, such as licensing, voluntary measures, and marine planning are not sufficient to meet the conservation aims of the MPA.

In 2014, the Scottish Government issued an urgent MCO for the first time to protect the fragile maerl bed ecosystems off the coast of the Isle of Arran, which had 'generally been considered to be in poor condition with a very low proportion of live maerl cover'⁴Nature Scot. (2014). South Arran MPA diver survey of maerl beds, kelp and seaweed communities on sublittoral sediment, and seagrass beds 2014. Retrieved from <a href="https://www.nature.scot/sites/default/files/2018-12/Publication%202018%20-%20SNH%20Research%20Report%20882%20-%20South%20Arran%20MPA%20diver%20survey%20of%20maerl%20beds%2C%20kelp%20and%20seaweed%20communities%20on%20sublittoral%20sediment%20and%20seagrass%20beds%202014.pdf" target="_blank">https://www.nature.scot/sites/default/files/2018-12/Publication%202018%20-%20SNH%20Research%20Report%20882%20-%20South%20Arran%20MPA%20diver%20survey%20of%20maerl%20beds%2C%20kelp%20and%20seaweed%20communities%20on%20sublittoral%20sediment%20and%20seagrass%20beds%202014.pdf</a> [accessed 21 February 2021]. The MCO included a prohibition on anchoring any vessel, depositing anything on the seabed, or removing anything from the seabed within the protected area without Scottish Ministers' authorisation.

Ⓒ COAST

Sites of Special Scientific Interest (SSSI) is a statutory designation made by NatureScot under the Nature Conservation (Scotland) Act 2004. Sites are selected after survey and evaluation against the Joint Nature Conservation Committee (JNCC) criteria, on the basis of special interest by reason of flora, fauna, geological, geomorphological or physiographical features. Scotland has 1,422 SSSIs, covering over one million hectares. SSSIs range in size from less than 1 hectare, to 29,000 hectares (the Cairngorms SSSI)¹NatureScot. (2020, August 3). Sites of Special Scientific Interest (SSSIs). Retrieved from <a href="https://www.nature.scot/professional-advice/protected-areas-and-species/protected-areas/national-designations/sites-special-scientific-interest-sssis#:~:text=Scotland%20has%201%2C422%20SSSIs%2C%20covering,to%20more%20than%2029%2C000%20hectares." target="_blank">https://www.nature.scot/professional-advice/protected-areas-and-species/protected-areas/national-designations/sites-special-scientific-interest-sssis#:~:text=Scotland%20has%201%2C422%20SSSIs%2C%20covering,to%20more%20than%2029%2C000%20hectares.</a> [accessed 18 March 2021].

Coastal habitats such as saltmarshes, sand dunes and machair are included in the guidelines for selecting SSSIs²Rees, S., Angus, S., Creer, J., Lewis, H., &amp; Mills, R. (2019). Guidelines for the selection of biological SSSIs. Part 2 Detailed guidelines for Habitats and Species. Chapter 1a Coastlands (coastal saltmarsh, sand dune, machair, shingle, and maritime cliff and slopes, habitats). Retrieved from <a href="https://hub.jncc.gov.uk/assets/36b59d93-8487-471d-9428-bc3d7dff0423" target="_blank">https://hub.jncc.gov.uk/assets/36b59d93-8487-471d-9428-bc3d7dff0423</a>. Seagrasses and kelp are also included as 'biotopes of interest' under the guidelines³Brazier, D.P., Hiorns, N., Kirkham, E., Singfield, C., Street, M., Steel, L., … Kent, F. (2019). Guidelines for the selection of biological SSSIs. Part 2 Detailed guidelines for Habitats and Species. Chapter 1b Marine Intertidal and Shallow Subtidal Habitats. Retrieved from <a href="https://hub.jncc.gov.uk/assets/3e8b58d8-ff6b-4bc6-ba4f-aeed92710e14" target="_blank">https://hub.jncc.gov.uk/assets/3e8b58d8-ff6b-4bc6-ba4f-aeed92710e14</a> [accessed 28 February 2021].

77.4% of Scottish saltmarshes lie with SSSIs⁴Nature Scot. (2017). Saltmarsh. Retrieved from <a href="https://www.nature.scot/landscapes-and-habitats/habitat-types/coast-and-seas/coastal-habitats/saltmarsh" target="_blank">https://www.nature.scot/landscapes-and-habitats/habitat-types/coast-and-seas/coastal-habitats/saltmarsh</a> [accessed 17 February 2021]. All sites that are over 1 km2 are under statutory protection. However, several large saltmarshes, such as the largest saltmarsh on the west coast of Loch Carron, are not designated as they are smaller than 1 km2⁵Burrows, M.T., Kamenos, N.A., Hughes, D.J., Stahl , H., Howe, J.A., &amp; Tett, P. (2014). Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment. Project Report. Scottish Natural Heritage, Edinburgh.. Seagrass beds within Dornoch Firth, Longman and Castle Stuart Bays, Loch Fleet, and Sunart are also protected as designated SSSIs.

SSSI management

Most SSSIs are in private ownership and the Scottish Government work with their owners and managers to ensure:

• Appropriate management of a site’s natural features

• All decision-makers are aware of the designation when considering changes in land use or other activities that might affect an SSSI

Under Section 19 of the Nature Conservation (Scotland) Act 2004, it is an offence for anyone to intentionally or recklessly damage the protected natural features of an SSSI.

Nature Conservation Orders

Under Section 23 of the Nature Conservation (Scotland) Act 2004, Scottish Ministers have powers to issue Nature Conservation Orders (NCOs) to protect any natural feature of land that is within an SSSI that is being actively damaged or when there is evidence that it is under threat of damage. The Orders set out certain prohibited operations and the land to which they apply. There are currently 6 NCOs in Scotland, primarily to prevent shellfish extraction or damage to rare fossils.

In 2017, decision making powers over a collection of rights, functions and assets encompassing the Crown Estate were devolved to Crown Estate Scotland (CES). CES is now responsible for:

• Managing approximately half the foreshore around Scotland

• Leasing of seabed out to 12 nautical miles

• Managing the rights to lease the seabed for offshore renewable energy, gas and carbon dioxide storage out to 200 nautical miles

Mechanical Kelp Harvesting

Kelp harvesting is the subject of another SPICe briefing.

The seabed around the Scottish coast is managed by CES, and any harvesting of seaweed (kelp) below the low tide mark requires a licence from them. Harvesting of seaweed from the foreshore (between the low water mark and the high water mark) may also require a licence in those areas managed by CES, which is approximately 50% of the Scottish coast.

Section 15 of the Scottish Crown Estate Act 2019, which came into effect on 1 October 2020, banned the commercial removal of wild kelp from the seabed in a means that prevents the regrowth of the kelp plant.

During the parliamentary scrutiny of the Scottish Crown Estate Act 2019 a review was announced to gather evidence to help ensure existing seaweed harvesting activity and future proposals are sustainable and Scotland’s marine environment is protected. Accordingly, a Seaweed Review Steering Group was established.

Scotland has a number of international commitments to conserve and protect biodiversity, which includes some of the blue carbon habitats outlined in this briefing.

The Ramsar Convention on Wetlands of International Importance is an international treaty for the conservation and sustainable use of wetlands. It is also known as the Convention on Wetlands.

All Ramsar sites are also Natura 2000 sites (a network of core breeding and resting sites for rare and threatened species and some rare natural habitat types) and/or Sites of Special Scientific Interest (SSSIs) and therefore, these sites often receive statutory protection under the Nature Conservation (Scotland) Act 2004.

The OSPAR Commission

The OSPAR Commission is an inter-governmental body responsible for overseeing the implementation of the 1992 Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention) - to which the UK is a party. The OSPAR Convention aims to prevent and eliminate pollution and protect the maritime area against the adverse effects of human activities.

The majority of Scotland's Seas are within OSPAR Region III (Celtic Seas) and Region II (Greater North Sea). There are also parts of Scotland's seas within Region V (wider Atlantic) and Region I (Arctic Waters).

At the OSPAR Commission meeting in Bremen in 2003, the UK committed to the following work being undertaken by 2010:

• Setting up a network of ecologically coherent OSPAR (See Marine Protected Areas)

• Analysis of listed human activities which are capable of causing adverse damage to the marine environment and the measures necessary to address this in the light of this analysis (See Assessment)

• Creation of an effective tool for integrating action across the whole marine environment via the North Sea pilot project, which aims to produce a coherent suite of ecological quality objectives

• Taking measures to protect coral reefs

The UK is a signatory of the Convention on Biological Diversity (CBD), which set 20 global targets, known as 2010 Aichi Biodiversity Targets, to be met by 2020. Target 11 is relevant to marine biodiversity:

By 2020, at least 17 percent of terrestrial and inland water, and 10 percent of coastal and marine areas, especially areas of particular importance for biodiversity and ecosystem services, are conserved through effectively and equitably managed, ecologically representative and well connected systems of protected areas and other effective area-based conservation measures, and integrated into the wider landscapes and seascapes.

Scotland's Strategy

In 2013, the Scottish Government published 'The Scottish Biodiversity Strategy: 2020 Challenge for Scotland’s Biodiversity', setting the strategies to achieve the 2010 Aichi biodiversity targets. In relation to Scotland's marine biodiversity, the plan states:

• Sustainable management of the seas to deliver multiple benefits will be assured through implementation of the Scottish Marine Nature Conservation Strategy and the National Marine Plan.

• An ecologically coherent network of Marine Protected Areas will protect the best of Scotland’s marine nature, promote sustainable use and aid recovery of commercially valuable fish and shellfish.

• An innovative system of marine planning will include all those with an interest in the marine environment to ensure the sustainable management of our seas, coasts and islands.

• Better understanding of the marine environment will help us identify the marine features most in need of protection, and give better advice on marine and coastal management.

• Coasts will be managed to help adapt to pressures from climate change

Scotland's Progress

In 2021, NatureScot published the latest update on Scotland's progress towards the Aichi targets. In the report, the following progress in relation to marine biodiversity is outlined:

The United Nations Sustainable Development Goals are a collection of 17 goals set in 2015 designed to be a 'blueprint to achieve a better and more sustainable future for all', intended to be achieved by 2030. These Goals underpin the Scottish Government's National Performance Framework.

Ⓒ United Nations

The 14th goal 'Life Below Water' aims to 'Conserve and sustainably use the oceans, seas and marine resources for sustainable development'. The goal is formed of 10 further targets split into:

1. Outcome targets:

   1. Reduce marine pollution

   2. Protect and restore ecosystems

   3. Reduce ocean acidification

   4. Sustainable fishing

   5. Conserve coastal and marine areas

   6. End subsidies contributing to overfishing

   7. Increase the economic benefits from sustainable use of marine resources

2. Means of achieving targets:

   1. To increase scientific knowledge into research and technology for ocean health

   2. Support small scale fishers

   3. Implement and enforce international sea law

The management of blue carbon habitats and stores with regards to their role in climate change mitigation can be considered to fall under two areas:

1. Protection of current carbon stores and habitats from key threats to maintain their storage of carbon and carbon sequestration rates, such that they do not become a source of carbon emissions in the future. Both the Marine Acts and Climate Change Acts provide opportunities for the policies and proposals to protect blue carbon, given its role in climate change mitigation.

2. The use of blue carbon habitats and ecosystems as a strategy to offset carbon emissions from human activities by increasing their sequestration potential through nature-based solutions or geoengineering. This also includes the protection and enhancement, for instance through restoration of coastal ecosystems, as a means to increase climate change resilience and adaptation.

Overview

Marine (Scotland) Act 2010 and Marine and Coastal Access Act 2009 (referred to as the Marine Acts) require Scottish Ministers to consider climate change mitigation and adaptation in setting out the objectives of the National Marine Plan and designating Marine Protected Areas. More generally, the Acts require Scottish Ministers and other public bodies when exercising powers to:

act in the way best calculated to mitigate, and adapt to, climate change so far as is consistent with the purpose of the function concerned.

This means that Scottish Ministers and public authorities must consider climate change mitigation and adaption during marine planning and management decisions.

National Marine Plan

The Marine Acts require Scottish Ministers, when setting out National and Regional Marine Plans, to outline:

objectives relating to the mitigation of, and adaptation to, climate change

The current National Marine Plan (NMP), due for review in 2021, considers climate change in two distinct ways. Firstly, the NMP considers how actions under the Plan might help mitigate the degree of human-induced climate change. Secondly, it considers how actions under the Plan need to be adapted to take into account the effects of climate change.

Concerning blue carbon stores, the NMP states, under General Policy Number 5 (4.19):

Reducing human pressure and safeguarding ecosystem services such as natural coastal protection and natural carbon sinks (e.g. seagrass beds, kelp and saltmarsh) should be considered. In some cases, compensatory habitat creation or enhancement may be possible and should be considered as a last resort if significant harm cannot be avoided. Appropriate proactive opportunities for enhancing natural carbon sinks and allowing natural coastal change where possible should also be considered.

The NMP draws attention to the role of regional marine planning in safeguarding carbon stores, stating that Regional Marine Plans should:

• Identify significant natural carbon sinks and seek to avoid co-location with potentially damaging activity; then

• Assess the acceptability of any proposed partial loss or damage to natural carbon sinks (including any compensatory measures) through licensing or management of marine activities, balanced with priorities presented in this Plan and respective regional marine plans.

• Explain how they have taken into account future climate change in terms of climate change adaptation. <applies to inshore waters only>

Regional Marine Plans

Section 5 of the Marine (Scotland) Act 2010 allows Regional Marine Plans to be developed by Marine Planning Partnerships (see MPA management). Regional Marine Plans are designed to take account of local circumstances and smaller ecosystem units, providing a more localised approach to assessing the marine environment.

There are currently no finalised regional marine plans. However, pre-consultation drafts of Regional Marine Plans for Clyde (Clyde Regional Marine Plan) and Shetland (The Shetland Islands' Marine Spatial Plan) have been developed. Both drafts outline policies for climate change mitigation in relation to the protection of known carbon stores.

For instance, the pre-consultation draft of the Clyde Regional Marine Plan states the following objectives and policies in relation to climate change mitigation and carbon stores:

• Objective CC.2: Natural carbon sinks and the associated benefits and services they provide are maintained and/or where possible enhanced in the Clyde Marine Region.

• Policy CC.2: Development(s) and/or activities will be supported where they can demonstrate that they will avoid damage to and/or, where possible, enhance the capacity of recognised carbon sinks in the Clyde Marine Region.

In addition, the draft Shetland Islands' Marine Spatial Plan states:

Policy MP CLIM1: Developments which have the potential to impact habitats which act as a carbon sink or protect against coastal erosion may be refused. In determining applications for development, consenting authorities should, where relevant, consider the likely impact of the proposed development on climate change, including any management and/or mitigation measures proposed by the developer. Developers may be asked to consider impacts on habitats which act as a carbon sink e.g. kelp forests and horse mussel beds.

In relation to the designation of Nature Conservation MPAs, Section 68 of the Marine (Scotland) Act 2010 states that:

In considering whether to designate an area, the Scottish Ministers may have regard to the extent to which doing so will contribute to the mitigation of climate change.

Scottish Ministers are therefore empowered to protect blue carbon, such as carbon 'hotspots' in seafloor sediments, on the basis that their disturbance (through a lack of protection) has the potential to result in significant CO2 emissions. However, based on a search of key public-facing documents and research on Scotland's MPA network¹Carruthers, M., Chaniotis, P.D., Clark, L., Crawford-Avis, O., Gillham, K., Linwood, M., … Wilson, E. (2011). Contribution of existing protected areas to the MPA network and identification of remaining MPA search feature priorities. Internal report produced by Scottish Natural Heritage, the Joint Nature Conservation Committee and Marine Scotland for the Scottish Marine Protected Areas Project.²Scottish Natural Heritage. (2014). NatureScot Commissioned Report 747: NatureScot's advice on selected responses to the 2013 Marine Scotland consultation on Nature Conservation Marine Protected Areas (MPAs). Retrieved from <a href="https://www.nature.scot/naturescot-commissioned-report-747-naturescots-advice-selected-responses-2013-marine-scotland" target="_blank">https://www.nature.scot/naturescot-commissioned-report-747-naturescots-advice-selected-responses-2013-marine-scotland</a> [accessed 13 March 2021]³Scottish Natural Heritage and the Joint Nature Conservation Committee. (2012). Advice to the Scottish Government on the selection of Nature Conservation Marine Protected Areas (MPAs) for the development of the Scottish MPA network. Scottish Natural Heritage Commissioned Report No. 547.⁴Scottish Government. (2018). Marine Protected Area Network - 2018 Report to the Scottish Parliament. Retrieved from <a href="https://www.gov.scot/publications/marine-protected-area-network-2018-report-scottish-parliament/" target="_blank">https://www.gov.scot/publications/marine-protected-area-network-2018-report-scottish-parliament/</a> [accessed 13 March 2021]⁵Scottish Government . (2017). Guidelines for Selecting &amp; Developing MPAs. Retrieved from <a href="https://www.webarchive.org.uk/wayback/archive/3000/https://www.gov.scot/Resource/0051/00515466.pdf" target="_blank">https://www.webarchive.org.uk/wayback/archive/3000/https://www.gov.scot/Resource/0051/00515466.pdf</a>, MPAs do not appear to have been designated on the basis of their contributions to climate change, and it is not clear that carbon storage/sequestration (within the context of climate change mitigation) has been considered in the designation of current or proposed future MPAs.

Currently, Nature Conservation MPAs are primarily designated on their basis of containing an MPA search feature, which protects some biological blue carbon habitats - but on the basis on their contribution to Scotland's biodiversity.

Scotland's Climate Change Plan, published in 2018, acknowledges the importance of blue carbon stores but does not contain any specific policies or proposals to protect known blue carbon stores or habitats. The Plan outlines the Scottish Government's £570,000 commitment to the Scottish Blue Carbon Research Forum, which aims to understand how marine and intertidal habitats sequester and store carbon and the effects of human activities on these habitats, to inform future policy.

Climate Change Plan 2018–2032 - Update

In late 2020, the Scottish Government published the draft update to the Climate Change Plan 2018 – 2032 (CCPu), setting out the strategy to meet the new emissions targets stipulated by the Climate Change (Emissions Reduction Targets) (Scotland) Act 2019. The update aims to achieve the dual targets of lifting an economy out of recession following the COVID-19 pandemic whilst protecting and improving the environment at the same time.

As with the CCP, the draft CCPu does not contain any specific policies or proposals relating to blue carbon stores. Instead, the CCPu refers to the Scottish Government's upcoming Blue Economy Action Plan, announced in the 2020-21 Programme for Government, in which the Government will:

• Provide leadership through collaboration and innovation, maximising the impact of public investment and developing better regulation to help manage the shared use of the seas by Scotland’s marine sectors, communities and ecosystems.

• Optimise opportunities in order to unlock the significant inclusive growth potential of Scotland’s marine space whilst supporting a transition to net zero.

Climate Change Policy and Marine Protected Areas

Since the publication of the Climate Change Plan in 2018, the Climate Change (Emissions Reduction Targets) (Scotland) Act 2019 was passed, setting greater targets for emissions reductions. The Act prompted the publication of the draft Update to the Climate Change Plan 2018–2032 (CCPu).

The Act additionally highlights the role of Marine Protected Areas in the protection of carbon stores and their consideration in subsequent climate change plans, stating under section 35(15) that:

The [Climate Change] plan must also set out the Scottish Ministers’ proposals and policies regarding the consideration of the potential for the capture and long-term storage of carbon when designating marine protected areas under section 67 of the Marine (Scotland) Act 2010.

During the 2021 parliamentary scrutiny of the draft CCPu, the Environment, Climate Change and Land Reform (ECCLR) committee heard evidence that the Scottish Blue Carbon Research Forum has provided a good understanding of where ‘carbon hotspots’ can be found in the marine environment¹Environment, Climate Change and Land Reform Committee. (2021, February 2). Official Report. Retrieved from <a href="http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf" target="_blank">http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf</a>. It further heard that the 2021 review of the National Marine Plan is an opportunity to examine spatial management of marine carbon and review how fisheries are managed. Therefore, as part of a broader suite of recommendations, the ECCLR committee recommended that the Scottish Government:

1. Provides clear guidance on the role of spatial management in protecting blue carbon hotspots from pressures such as mobile bottom-contacting fishing gear.

2. Ensures that blue carbon storage and sequestration capacity is taken into account in proposals for management measures in Marine Protected Areas.

Parliamentary scrutiny of the CCPu

During parliamentary scrutiny of the draft CCPu, the Environment, Climate Change and Land Reform Committee (ECCLR) drew attention to the lack of policies and proposals relating to the protection of blue carbon in the CCPu. The ECCLR committee heard evidence of the research emerging from the Scottish Blue Carbon Forum of 'hotspots for carbon burial' in Scotland's seas¹Environment, Climate Change and Land Reform Committee. (2021, February 2). Official Report. Retrieved from <a href="http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf" target="_blank">http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf</a>³Environment, Climate Change and Land Reform Committee. (2021, February 21). 4th Meeting Agenda - Climate Change Plan: Evidence sessions with stakeholders. Retrieved from <a href="https://www.parliament.scot/S5_Environment/Meeting%20Papers/ECCLR_2021.02.02_Meeting_papers_(public).pdf" target="_blank">https://www.parliament.scot/S5_Environment/Meeting%20Papers/ECCLR_2021.02.02_Meeting_papers_(public).pdf</a>⁴Smeaton, C., Hunt, C.A., Turrell, W., &amp; Austin, W. (2021). Marine sedimentary carbon stocks of the United Kingdom’s Exclusive Economic Zone. Frontiers in Earth Science.. The scrutiny culminated in the Environment, Climate Change and Land Reform Committee (ECCLR) recommending that the Scottish Government⁵Environment, Climate Change and Land Reform Committee. (2021, March 4). ECCLR Committee response to the draft updated climate change plan (CCPu). Retrieved from <a href="https://www.parliament.scot/S5_Environment/Reports/ECCLR_2021.03.04_OUT_CS_CCPu_Report.pdf" target="_blank">https://www.parliament.scot/S5_Environment/Reports/ECCLR_2021.03.04_OUT_CS_CCPu_Report.pdf</a>:

1. Brings forward policies on how to protect blue carbon stores through the forthcoming update of the National Marine Plan and the development of the Blue Economy Action Plan and reflects this intention in the final CCPu.

2. Provides clear guidance on the role of spatial management in protecting blue carbon hotspots from pressures such as mobile bottom-contacting fishing gear.

3. Ensures that blue carbon storage and sequestration capacity is taken into account in proposals for management measures in Marine Protected Areas.

4. Provides further information on how it will ensure that the Blue Economy Action Plan reconciles the need to ensure protection of natural capital such as blue carbon and marine biodiversity hotspots with socioeconomic priorities of coastal communities.

5. Works with the UK Department for Business, Energy and Industrial Strategy to incorporate blue carbon in saltmarsh and seagrass ecosystems into the UK's National Atmospheric Emissions Inventory and therefore Scotland’s greenhouse gas inventories.

6. Takes a leadership role in promoting the opportunities of blue carbon and presses for the inclusion of blue carbon in the GHG inventory, including with the UK Government and in the COP26 negotiations.

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In it's 2021 recommendations to Government on the Update to the Climate Change Plan (CCPu), the Environment, Climate Change and Land Reform (ECCLR) Committee recommended that the Scottish Government:

1. Works with the UK Department for Business, Energy and Industrial Strategy to incorporate blue carbon in saltmarsh and seagrass ecosystems into the UK's National Atmospheric Emissions Inventory and therefore, Scotland’s greenhouse gas (GHG) inventories.

2. Takes a leadership role in promoting the opportunities of blue carbon and presses for the inclusion of blue carbon in the GHG inventory, including with the UK Government and in the COP26 negotiations.

What is a greenhouse gas (GHG) inventory?

A greenhouse gas (GHG) inventory is an accounting of all the emissions and uptake of greenhouse gases and is central to developing strategies to reach net-zero. Blue carbon ecosystems are not currently incorporated into Scotland's GHG inventories, and therefore are not considered in Scotland's targets towards reaching net zero.

Scottish greenhouse (GHG) inventories are calculated by the National Atmospheric Emissions Inventory (NAEI), led by the UK Department for Business, Energy, and Industrial Strategy (BEIS). The data and methods used to derive GHG inventories have been developed to be consistent with methods defined within international guidance provided to all countries via the Inter-governmental Panel on Climate Change (IPCC). All countries that report to the United Nations Framework Convention on Climate Change (UNFCCC) must use these estimation methods from the agreed guidelines and good practice to ensure that the GHG emissions for each country are complete and comparable.

Blue Carbon and GHG Inventories

Currently, the UK's NAEI does not include biological or geological blue carbon ecosystems to calculate GHG inventories. However, on an implementation level, mangroves, salt marshes and seagrasses can be included in national accounting, according to the IPCC 2013 Supplement to the 2006 Guidelines for National Greenhouse Gas Inventories: Wetlands¹IPCC. (2014). 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands. Retrieved from <a href="https://www.ipcc.ch/publication/2013-supplement-to-the-2006-ipcc-guidelines-for-national-greenhouse-gas-inventories-wetlands/" target="_blank">https://www.ipcc.ch/publication/2013-supplement-to-the-2006-ipcc-guidelines-for-national-greenhouse-gas-inventories-wetlands/</a> [accessed 21 February 2021]. This supplement has been used by BEIS to develop and implement a new method for reporting GHG emissions from peatlands in the UK’s emissions inventory. These guidelines provide ready opportunities for BEIS to incorporate saltmarshes and seagrasses into UK GHG inventories. Currently, there are no internationally-recognised frameworks for incorporating sedimentary carbon stores into the calculation of national GHG inventories.

What are Nature-based Solutions?

Nature-based Solutions (NbS) are defined by the International Union for the Conservation of Nature as:

actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits.

Ⓒ IUCN

It is estimated that annually 1,000 km2 of coastal blue carbon habitats are lost across the globe, emitting 500 Mt CO2 per year¹National Academies of Sciences, Engineering, and Medicine. (2019). Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press.. Therefore, restoration of blue carbon habitats is recognised as an effective nature-based solution (particularly mangroves, saltmarshes and seagrasses), not only a means to prevent additional emissions and increase carbon sequestration globally but to also increase the climate-change resilience for local communities (see Climate Change Adaptation Programme). This is alongside a host of other biodiversity and ecosystem benefits.

Coastal ecosystems, in particular, are seen as an attractive nature-based solution, as their carbon sequestration per unit area of restored land is often high compared with terrestrial environments. This is demonstrated in Scotland: healthy saltmarshes are predicted to sequester around 440 g CO2-eq per m2 per year, greater than the sequestration potential of Scottish peatlands (48 - 280 CO2-eq per m2 per year) and similar to Scottish forestry sequestration (190 - 700 CO2-eq per m2 per year).

The recognition of blue carbon habitats as effective nature-based solutions has led to the development of international frameworks to facilitate restoration projects. For instance, The Nature Conservancy has partnered with The International Union for Conservation of Nature IUCN) to develop a global model and map of mangrove restoration potential to help practitioners prioritise areas²Worthington, T., &amp; Spalding, M. (2018). Mangrove Restoration Potential: A global map highlighting a critical opportunity. Retrieved from <a href="https://oceanwealth.org/wp-content/uploads/2019/02/MANGROVE-TNC-REPORT-FINAL.31.10.LOWSINGLES.pdf" target="_blank">https://oceanwealth.org/wp-content/uploads/2019/02/MANGROVE-TNC-REPORT-FINAL.31.10.LOWSINGLES.pdf</a>, and as a way to support and encourage mangrove restoration projects globally.

Scotland's Climate Change Plan (CCP) does not currently contain policies or proposals for blue carbon NbS, but contains policies for forestry and peatland NbS. In the draft update to the Climate Change Plan, the Scottish Government states it:

is committed to deploying nature-based solutions at scale and in a sustainable and managed way and that nature-based solutions will form a key part of the coordinated approach to climate change, biodiversity, infrastructure, planning, land use, marine and economic strategies

The CCP and CCPu specifically set out to use NbS in two key ways: restoration of 250,000 ha of degraded peatland and increasing forest cover by 21% by 2032.

Saltmarsh Restoration

There are currently no policies to manage coastal wetlands (such as saltmarshes) as Nbs approaches. However, during 2021 scrutiny of the update to the climate change plan, the Environment, Climate Change and Land Reform (ECCLR) Committee heard evidence that saltmarshes can be managed through coastal realignment¹Environment, Climate Change and Land Reform Committee. (2021, February 2). Official Report. Retrieved from <a href="http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf" target="_blank">http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf</a>, which also provides benefits for biodiversity, providing multiple ecosystem services. The ECCLR Committee heard that that linking rural policy and environmental land management schemes is a mechanism for delivering this¹Environment, Climate Change and Land Reform Committee. (2021, February 2). Official Report. Retrieved from <a href="http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf" target="_blank">http://www.parliament.scot/parliamentarybusiness/report.aspx?r=13096&amp;mode=pdf</a>.

Despite not being included in policies and proposals, restoration of blue carbon ecosystems is ongoing in Scotland. Saltmarsh restoration in Scotland is already showing evidence of benefits to carbon storage and biodiversity. However, it is uncertain whether saltmarsh restoration in Scotland alone offers a significant additional carbon sequestration capacity in the context of Scotland's net-zero ambitions, as Scotland only has 14% of the UK's saltmarsh areal extent. There has also been little research into whether other coastal and marine habitats in Scotland are viable NbS. Regardless of the impact of restoration on additional carbon sequestration, restoration still provides known benefits for coastal protection and resilience and biodiversity.

Current saltmarsh restoration projects

Saltmarsh restoration projects are ongoing as a natural solution to the increasing problem of coastal erosion, and provide opportunities to increase carbon sequestration of coastal ecosystems. Saltmarsh restoration efforts on the Eden Estuary in Fife have taken place since 1999, using direct transplants from donor marsh sites within the estuary to enhance degraded saltmarsh and extend areas of saltmarsh³Maynard, C., McManus, J., Crawford, R.M., &amp; Paterson, D. (2011). A comparison of short-term sediment deposition between natural and transplanted saltmarsh after saltmarsh restoration in the Eden Estuary (Scotland). Pkant Ecology &amp; Diversity , 4, 103-113.. Restoration projects provide a valuable system in which to study the development of restored areas to sequester and store carbon. Restoration has increased the total amount of carbon stored in sediment and vegetation by over 0.5 t, by promoting greater carbon burial⁴Taylor, B. (2019). Saltmarsh restoration and blue carbon dynamics in a Scottish estuary. Retrieved from <a href="https://research-repository.st-andrews.ac.uk/handle/10023/20891" target="_blank">https://research-repository.st-andrews.ac.uk/handle/10023/20891</a> [accessed 15 February 2021]. However, given the relatively small spatial extent of saltmarshes, saltmarshes' utility as a significant additional carbon store is predicted to be small⁴Taylor, B. (2019). Saltmarsh restoration and blue carbon dynamics in a Scottish estuary. Retrieved from <a href="https://research-repository.st-andrews.ac.uk/handle/10023/20891" target="_blank">https://research-repository.st-andrews.ac.uk/handle/10023/20891</a> [accessed 15 February 2021]. In the future, it is projected that the value of saltmarshes as a carbon store will increase as their area and health increases.

Saltmarsh restoration is also predicted to provide additional benefits such as enhanced biodiversity and coastal flood protection, which remain active areas of research. Saltmarsh restoration in the Eden Estuary found that 2-3 years after restoration the abundance and diversity of benthic macrofaunal organisms (organisms greater than 0.5 mm that live on, in, or at the sediment-water interface) was comparable to natural salt marsh sites⁶Wade, K. (2018). The biodiversity, ecosystem functioning and value of restored salt marshes in the Eden Estuary, Scotland. Retrieved from <a href="https://research-repository.st-andrews.ac.uk/handle/10023/17541" target="_blank">https://research-repository.st-andrews.ac.uk/handle/10023/17541</a> [accessed 12 February 2021]. The coastal defence provision of restored saltmarshes was equivalent to natural salt marsh sites following 10 years. The research also indicated that local communities prefer and are willing to pay more to support nature-based coastal defences, like saltmarshes, within the Eden Estuary.

Ⓒ Clare Maynard

In addition to storing carbon, coastal ecosystems (such as saltmarshes, dune and machair) play a key coastal defence role by dissipating wave energy. Climate change is associated with changes in sea storminess and wave intensity, and therefore the importance of coastal wetlands in climate change resilience has been acknowledged in Scottish Government's Climate Change Adaptation Programme.

The Climate Change Adaptation Programme does not lay out any specific policies or proposals which protect coastal wetlands but draws attention to measures in place to protect marine environments and habitats through the National Marine Plan and the Scottish Biodiversity Strategy.

Protection of Coastal Environments

Scotland's Dynamic Coast project, a project commissioned by the Scottish Government to deliver an assessment of coastal changes, to support Scotland's Climate Change Adaptation Programme recently reported that¹Hansom, J.D., Fitton, J.M., &amp; Rennie, A.F. (2017). Dynamic Coast - National Coastal Change Assessment: Coastal Erosion Policy Context, CRW2014/2. Retrieved from <a href="http://www.dynamiccoast.com/files/reports/NCCA%20-%20Coastal%20Erosion%20Policy%20Context.pdf" target="_blank">http://www.dynamiccoast.com/files/reports/NCCA%20-%20Coastal%20Erosion%20Policy%20Context.pdf</a> [accessed 24 February 2021]:

Whilst consideration of coastal erosion and its links with coastal flooding and the combined anticipated increase associated with climate change is acknowledged within national policies, there appears to be little or no consideration given to the types of adaptation policies and financial levers which will be required to manage both existing and future risk.

The transition to net-zero has given rise to a number of technological advancements to enhance carbon sequestration or store carbon. For example, the Scottish Government's draft Climate Change Plan Update relies on the use of negative emissions technologies (NETs) such as carbon capture and storage, where emissions from fossil fuels are injected into geological stores (e.g. empty oil and gas reservoirs).

Another strategy to enhance atmospheric carbon removal is geoengineering. Geoengineering is the deliberate large-scale manipulation of an environmental process that affects the earth's climate in an attempt to counteract the effects of global warming.

Ⓒ World Meteorological Association

Blue carbon habitats with their natural carbon sequestration capacity have inspired the development of geoengineering strategies. For example, blue carbon-based geoengineering techniques include mass macroalgal(kelp) cultivation and ocean fertilisation to stimulate phytoplankton blooms. However, the success of these techniques depends on the fate of the carbon once it has been sequestered from the atmosphere. To be effective, the carbon in living biomass must either:

1. Enter long-term carbon storage (i.e. into geological seafloor sediments¹Chung, I.K., Sondak, C.F.A., &amp; Beardall, J. (2017). The future of aquaculture in a rapidly changing world. European Journal of Phycology, 52, 495-505.) or

2. Be harvested before it degrades (e.g. harvesting kelp for aquaculture).

Numerous factors influence how much carbon from kelp or phytoplankton biomass is subsequently stored long-term in marine sediments, such as oxygen levels in the water column, productivity, and mixing processes²GESAMP. (2019). High level review of a wide range of proposed marine geoengineering techniques”. (Boyd, P.W. and Vivian, C.M.G., eds.). (IMO/FAO/UNESCO-IOC/UNIDO/WMO/IAEA/UN/UN Environment/ UNDP/ISA Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection). Retrieved from <a href="http://www.gesamp.org/publications/high-level-review-of-a-wide-range-of-proposed-marine-geoengineering-techniques" target="_blank">http://www.gesamp.org/publications/high-level-review-of-a-wide-range-of-proposed-marine-geoengineering-techniques</a>. If not managed correctly, promoting kelp or phytoplankton can lead to negative impacts. For instance, if phytoplankton (microalgae) blooms do not sink through the water, they can degrade on the sea surface, rapidly consuming oxygen and leading to mass fish mortality. Ensuring that blue carbon based geoengineering strategies do not have detrimental effects is an area of ongoing research.