# Assessment of Ecosystem Services across the Land-Sea Interface in Baltic Case Studies
## 4 Discussion
### Transferability of the Approach  
The spatial habitat typology presented in this study was tested in three Southern Baltic CSS. Our approach to build the habitat typology upon existing spatial definitions of the WFD and HD was beneficial. Geospatial data was easily accessible from public geoportals or could be acquired from public authorities responsible for policy implementation. Since all EU member states are required to regularly provide geospatial data on the distribution of WFD water bodies and HD habitats, the approach can be generally transferred to other EU member states. This was successfully shown through the application to the Lithuanian CSS. However, one has to keep in mind that our definition of marine habitats is based on the water body classification of the German Baltic Sea, which is characterized by brackish waters and mostly low hydrodynamic properties. Thus, for an application within the North Sea/Atlantic Ecoregion, which is characterized by higher salinities and hydrodynamic properties, additional marine habitats need to be defined for the spatial typology. Likewise, additional CLC types and coastal habitats (based on the HD habitat types) might be needed when transferring the approach to other areas. Consequently, we presume that a direct application of the spatial habitat typology is only possible within the Southern Baltic Sea Region. Nevertheless, the general approach of defining coastal and marine habitats based on WFD water bodies, HD habitats, and seabed sediments is transferable to other EU countries. Spatial habitat maps are further needed for the inclusion of ES assessments in the MSFD or MSP Directive. A more detailed assessment of ES in the Baltic Sea is also foreseen for the next Holistic Assessment of the Baltic Sea (HELCOM HOLAS III) report, which supports the implementation of the MSFD in the Baltic Sea. However, studies by [PERSON] et al. [58] and [PERSON] et al. [59] show that marine ES assessments are lacking for most parts of the Baltic Sea. In its current version, our spatial habitat typology is limited to the 12 nautical mile zone and thus only covers territorial waters. Thus, a spatial extension would be needed to allow for applications within the scope of the MSFD or MSP Directive. In line with the WFD classification, we separate coastal and marine surface waters by the 15 m isobaths, and classified all marine waters (up to 12 nm) as 'Open coastal waters: seasonally stratified'. The implications of this approach are visible in the spatial maps of the Lithuanian CSS, which includes a large share of marine waters that are mostly covered by a single, homogenous habitat type. For the purpose of assessing differences across land and sea, the spatial definition was found to be sufficient. However, a better differentiation of marine waters is needed for national or Baltic Sea wide ES assessment. This should be based on the HELCOM sub-basins and further differentiation using the aphotic benthic habitats of the HELCOM HUB classification, which provide the necessary information of seabed sediments and habitats. Since the geospatial data required for the extension is publicly available in in the HELCOM Map and Data Service [51], it could be easily implemented. The HELCOM HUB classification is also used as background for other ES assessments in the Baltic Sea. For instance, [PERSON] et al. [60] developed an ES assessment tool which assesses the contribution of HELCOM habitats to ecosystem functions and services. Being based on the initial \"ES potential matrix for terrestrial, coastal and marine ecosystem types of Northern Germany\" by [PERSON] et al. (2018), we assumed that our Baltic ESP Matrix is generally applicable for all CSS. This is certainly a simplification, especially with regard to an application in Lithuania. [PERSON] et al. (2016) recommend that existing ES matrices cannot be directly applied in different contexts or regions without being re-evaluated.