SNH: sustainable stewardship of Scotland’s seas helps them act as vast carbon sink

The global ocean plays a vital role in trapping and storing atmospheric carbon dioxide – a greenhouse gas – that would otherwise remain in the atmosphere and contribute to global warming.

Scotland has around 470,000 square kilometres of seas in which more than 1.7 billion tonnes of inorganic carbon, in the form of calcium carbonate, are stored as non-living material such as mollusc and crab shells, and the skeletons of microscopic plants (phytoplankton) coral, and maerl.

So-called ‘blue’ carbon is captured and stored across a range of seabed types such as kelp forests, saltmarsh, seagrass beds, cold-water coral reefs, flame shell and mussel beds and maerl that play a vital role in tackling climate change, much the same as onshore peatlands.

But these habitats face challenges – maerl beds and coral reefs are subject to climate change and trawling, while seagrasses and saltmarsh can be affected by coastal erosion and various development activities. When damaged, these habitats cannot retain as much carbon and may become a source of greenhouse gases.

Many of these carbon storing habitats are on a list of features which could receive protection under a Nature Conservation Marine Protected Area (MPA). After a recent public consultation the Scottish Government announced 30 Nature Conservation Marine Protected Areas (MPAs) around Scotland.

The new report: ‘Assessment of carbon budgets and potential blue carbon stores in Scotland’s coastal and marine environment’ states that ocean acidification could affect animals with hard shells, and may also cause erosion of dead calcareous material – thus releasing carbon back into the environment.

John Baxter, SNH’s principal marine adviser said: “Scotland’s seas fulfil many important services but one that has been largely overlooked until recently is the capacity to store vast carbon deposits. This makes it clear that good stewardship of these habitats is an essential part of our strategy to combat climate change.

“The report aimed to produce the first comprehensive review of the carbon budgets of a range of potential Scottish marine carbon stores. These include saltmarsh, seagrass beds, kelp forest, maerl beds, biogenic reefs, cold water corals and soft sediments. It also presents estimates of the extent of these different habitats around Scotland and their capacity to trap and store carbon in the short, medium or long term.”

Mike Burrows from the Scottish Association for Marine Science, the principal author of the report, said: “By combining information on growth and other processes with the extent of different parts of the ecosystem, we were able to show that most of the carbon captured in Scottish seas is by microscopic plants in surface waters.

“The biggest stores of carbon are where these plants become buried in soft sediments after sinking into deep water. Coastal plants, like kelp and seagrasses, capture a large amount of carbon, less than the plankton, but no less important. Those many animals that build shells, like corals, clams and mussels, capture less carbon but that shell material locks carbon away immediately for a very long time.

“All the coastal plants and animals are potentially vulnerable to local impacts, but the effect of climate change is probably the biggest and least understood effect on the rate of capture and storage of carbon in Scottish seas.”

ENDS