Exploring Sublittoral Blue Carbon Habitat Suitability and Potential in the Shetland Islands

This report presents the first assessment of sublittoral blue carbon habitats within the Shetland Islands 12 nm limit, evaluating their spatial extent, ecological characteristics, and potential contribution to carbon sequestration and long-term storage. Blue carbon habitats-including seagrass meadows, kelp forests, brittlestar beds, horse mussel beds and maerl beds-play a crucial role in supporting biodiversity, stabilising sediments, and mitigating climate change through the capture and retention of organic carbon (OC). The study combined high-resolution spatial data with species distribution modelling (MaxEnt) to predict the extent of blue carbon habitats across Shetland's 12 nautical mile (nm) zone. Modelled habitat distributions were developed using presence-only occurrence data and 11 environmental predictors. Validation metrics demonstrated high predictive accuracy (AUC > 0.97, TSS > 0.79), providing high confidence in the outputs. Key findings * : • Blue Carbon Habitat Extent o Total mapped blue carbon habitats cover 19.15 hectares, o Habitat suitability modelling suggests a potential extent of 62 km², o Seabed sediments (dominated by mixed and coarse sediments) cover 12 044 km². • Carbon Storage Potential o Combined mapped and predicted blue carbon habitats carbon storage potential was estimated at 6 358 tonnes (t) OC, with a potential annual production of 7 950 t C / yr. ▪ Known maerl beds are estimated to hold the equivalent of ~446 tonnes of CO2, while Shetland's seagrass meadows could hold ~92 tonnes, with an ~6 tonnes potentially sequestered each year. ▪ Carbon stored in the known blue carbon habitats is equivalent to the annual emissions of over 100 Shetland residents, or over 2.5 million miles of car travel. ▪ The annual carbon capture potential of Shetland's seagrass meadows alone is equivalent to the emissions from making 149 000 cups of tea or almost 30 million internet searches. o Seabed sediments were identified as the dominant long-term carbon reservoir, with an estimated OC stock of 1 353 kt and an annual storage capacity of 319 kt OC / year. Despite their limited mapped extent, blue carbon habitats demonstrate high carbon density potential, with seagrass meadows containing eight times more carbon per unit area than sand and maerl beds containing four times more. * All carbon stock and storage capacity estimates refer specifically to the top 10 cm of sediment.