# Assessment of Ecosystem Services across the Land-Sea Interface in Baltic Case Studies
## 2 Materials and Methods  
### Spatial Habitat Typology for Land and Sea  
To enable a joint spatial ES assessment across land and sea, we developed a spatially explicit typology for coastal and marine systems, which can complement the CLC classification that is based on satellite images and most commonly used in matrix-based assessments [16; 27]. Our typology builds upon spatial units of the WFD and the HD, since they are commonly accepted and applied across Europe. The WFD typology subdivides coastal and marine waters into comparable water bodies, based on factors such as latitude, longitude, tidal range, depth, current velocity, residence time, and salinity. Therefore, water bodies, the management units of the WFD, which belong to the same surface water type, share many abiotic and biotic similarities. To reflect the three-dimensional character of aquatic systems, we added sediment and benthic habitat characteristics, based on the HD, which includes a list of habitat types and species of community interest. It is closely related to the EUNIS classification [28], which provides a hierarchical framework for coastal waters and marine habitats and formed the basis for an EU-wide assessment of the distribution of marine ES [21]. We used the WFD typology of surface water types in German coastal waters of the Baltic, namely oligohaline inner coastal waters (B1), mesohaline inner coastal waters (B2), mesohaline open coastal waters (B3), and mesopolyhaline open coastal waters, seasonally stratified (B4). This typology covers only coastal waters up to one nautical mile off the national baseline (a simplified coastline). We extended the WFD approach to marine surface waters so that all German territorial waters up to 12 nautical miles are covered. In line with the WFD classification, we separate coastal and marine surface waters by the 15 m isobaths. According to this distinction, coastal waters comprise the shallow, light-penetrated, and wave-influenced waters up to 15 m depth. Marine waters are deeper than 15 m. Therefore, they have a reduced vertical exchange and are potentially seasonally stratified, bearing the risk of hypoxia. Hence, all marine waters are included in the WFD surface water type B4. Water body types B1 to B3 were further subdivided according to selected benthic habitat types, which were based on HD and HELCOM underwater habitat and biotope types (HELCOM HUB). This includes different sediment types, mud- and sand flats, vegetation, and reefs. In total, 10 marine habitat types were included in the matrix structure of the Baltic Ecosystem Service Potential Matrix (Baltic ESP Matrix). For the terrestrial areas, we included all CLC types (CLC 2018), which are present in the German Baltic Sea Region, which comprises the federal states Schleswig-Holstein and Mecklenburg-Western Pomerania. This covers 28 CLC types, which form the terrestrial ecosystem types of the Baltic ESP Matrix. Coastal ecosystem types, which are partly covered by the CLC classification, were redefined according to the HD and HELCOM coastal habitat types (e.g.,'sea dunes','sea cliffs, shingle, and stony beaches', and'salt marshes and salt meadows') and resulted in four coastal ecosystem types. Different geodata served as a base for the derivation of ecosystem types. Relevant information and data sets were obtained from geoportals and national and regional authorities. They were processed and, if applicable, transformed individually for the three zones, terrestrial, coastal, and marine. Afterwards, the data sets were merged in order to come up with one integral spatial layer. As overlaps between the different data sets occurred, they have been assigned different priorities based upon their spatial resolution, accuracy, and relevance for the assessment. Highest priority has been assigned to the coastal data set, followed by the data on the ecosystems in the marine areas. The terrestrial information based upon the CLC10 data sets has been set with the lowest priority.