In this study, the blue carbon resources in each Nature Conservation Marine Protected Area (NC MPA) and Special Area of Conservation (SAC) in Scotland’s inshore waters are estimated from the i) contributions of biological material to fixation of carbon, also referred to as production, and ii) contributions of geological sediments to blue carbon storage, following on from shelf-wide estimates in an earlier study (Burrows et al. , 2014). The methodology has been developed here to allow local-scale estimation of habitat extent and provides estimates of blue carbon associated with habitats and surface sediments.
- Combined, the SACs and NC MPAs (subsequently referred to as inshore MPAs) considered in this study cover 11 350 km2. Stocks of carbon within the habitats and surface sediments of inshore MPAs are estimated at 9.4 million tonnes (Mt) organic carbon and 47.8 Mt inorganic carbon; 1.6% of the estimated total of 592 Mt organic carbon (revised Burrows et al., (2014) value) and 2.7% of the total 1 739 Mt inorganic carbon across Scotland’s seas.
- Blue carbon habitats in the inshore MPA network are estimated to produce 248 000 t organic carbon and 36 000 t inorganic carbon per year, while sediment stores in the inshore MPAs accumulate 126 000 t organic carbon and 348 000 t inorganic carbon per year. Blue carbon production by seabed habitats is estimated to represent 0.6% of the total organic carbon assimilated, or 14% of the total produced by attached plants (including maerl).
- Sediment stores in inshore MPAs sequester 1.8% of total organic carbon across Scotland’s seas. The estimate of the total amount of inorganic carbon production in inshore MPAs is less reliable but represents a much larger proportion of the total, than for organic carbon production. This is because of the focus of inshore MPAs on areas of carbonate production such as maerl beds and cold water coral reefs.
- Threats to organic carbon stores are from physical disturbance, moorings, coastal developments, and renewable energy) of the sea bed, causing breakdown of previously buried material. Ocean acidification may pose a threat to inorganic carbon in sediments stored as carbonate but the mechanisms whereby that threat may be realised are as yet unclear. Ocean acidification also may have a direct negative effect on the capacity of calcareous reef builders and maerl to build carbonate skeletons, but algae such as kelp may benefit through enhanced photosynthesis due to higher CO2 levels.
- There are limitations in the estimates produced. Much of the information used in this assessment of blue carbon stocks is based on legacy data, some from older, published sources. Spatial extents of blue carbon habitats at the scales required for this report are poorly constrained. Finally, the science of understanding the effects of climate change on these systems is very much in its infancy and new developments will allow a much better informed outlook for the fate of these stocks and flows in a changing world. By establishing a methodology that integrates existing knowledge and understanding of blue carbon it should be possible to update reports such as this as new information emerges.
- This report aims to provide a starting point and a methodology for the examination of blue carbon storage in an MPA network. It is clear throughout the report that there is paucity within the data set. Despite these difficulties, and the uncertainty around accurate values of estimates, the general conclusions are unlikely to change with more detailed information. Therefore, the authors believe that enough information exists to begin to make conclusions about the importance of blue carbon stocks in the marine environment, both within Scotland and globally if the methods used are employed elsewhere. Variable and limited data will be a common feature of MPA networks throughout the world. The methodology proposed allows conclusions to be made on incomplete data, providing the beginnings of a management tool to aid protection of blue carbon in the marine environment.