The distribution of potential blue carbon habitats in Sweden

The distribution of coastal habitats has major implications for biodiversity, population dynamics and various ecosystem services such as protection against erosion, nutrient uptake and blue carbon (BC) storage. Therefore, mapping of habitats in the coastal zone is essential and a prerequisite for understanding their spatiotemporal distribution and configuration. In this study, we compiled existing data based on remote sensing, spatial statistical modelling and ground-truth surveys to map the distribution of established (i.e. saltmarshes and seagrass meadows) and potential BC habitats (including other rooted submerged macrophytes besides seagrass and coastal forested wetlands) along the entire Swedish coastline. The coast was delimited to areas on land with an elevation of 5 meters or less and shallow-water areas down to a depth limit of approximately 6 m. Additionally, as a proxy for the effects of land-based human activities on the mapped BC habitats, a landscape analysis based on the distance to and total area of agricultural and urban areas in Sweden’s coastal drainage basins was carried out. The total area of BC habitats was estimated to be around 1900 km², corresponding to about 30% of the total delimited Swedish coastal area. Seagrass meadows and shallow-water areas dominated by other rooted submerged macrophytes were the dominating BC habitats, covering approximately 1000 km² and 500 km², respectively. Following the natural salinity gradient along the Swedish coastline, seagrass meadows dominated in the marine environment on the Swedish west coast (including the Skagerrak, Kattegat and the Öresund area) and the southern part of the brackish Baltic Proper, while other rooted submerged macrophytes were primarily found at low salinity levels (~5 PSU and lower) in the northern Baltic Proper, Bothnian Sea and Bothnian Bay. The distance- and area-based landscape analysis showed that around 23% of the mapped BC habitats are areas potentially moderately to highly affected by land-based activities. BC habitats inside protected areas were found to be at a significantly lower risk compared to habitats outside protected areas (p < 0.05), but still around 24% (corresponding to an area around 130 km²) of the protected BC habitats are potentially moderately to highly affected by land-based activities. This nationwide mapping of both established and potential BC habitats shows that a large proportion of the long Swedish coastal zone includes BC habitats with great potential for supporting climate change mitigation and adaptation. Furthermore, this study contributes with important baseline information useful for assessing all possible BC habitats along the Swedish coastlines and highlights the importance of coastal management and marine spatial planning for the conservation of these habitats.