# Assessment of Ecosystem Services across the Land-Sea Interface in Baltic Case Studies
###### Abstract  
Spatial assessments of ecosystem services (ES) are needed to fulfil EU policy requirements and to support practical applications of the ES concept in policy implementation. So far, ES assessments have largely focused on terrestrial systems. A joint approach for land and sea is especially lacking. To overcome this gap, we present a novel spatial habitat typology and ES classification for an assessment across the land-sea interface. We build upon existing approaches and common spatial definitions, like CORINE land cover (CLC) types, water bodies of the Water Framework Directive (WFD), and habitat types according to the Habitats Directive (HD). We show applications of the resulting ES matrix for an expert-based assessment of ES potentials in three Baltic study sites (Schlei, Greifswald Bay and Curonian Lagoon). A complementary indicator-based approach to assess ES flows is introduced and applied. It enables a quantification of ES potentials and flows and ensures comparability among case study sites. Comparisons between the results for ES potentials and flows show that development capacities exist in particular for provisioning ES for marine habitats. Our approaches are spatially expandable and transferable and could be applied to support environmental policy implementation. Further, we discuss their practical relevance, current limitations, and future research perspectives. Water Framework Directive; Biodiversity Strategy; habitats directives; ecosystem service potential; ecosystem service flow; matrix; experts; coastal and marine management  
17 November 2021 10 December 2021 10 December 2021 12  
Since the adoption of the EU Biodiversity Strategy in 2011, much research on approaches to map and assess ES has been conducted on an EU, national and regional level [7]. However, so far, spatial ES assessments have largely focused on terrestrial systems. Approaches for marine systems lag behind and are often restricted to a small number of ES [8; 9]. Particularities, such as knowledge and data gaps, as well as the three-dimensional character of aquatic systems, pose challenges and have hampered ES assessments of marine systems [10]. Joint approaches to map and assess ES at land and sea are particularly rare [9]. However, activities taken at land also affect the coastal and marine environment and need to be regarded holistically. For instance, fertilization of agricultural fields is a major source for coastal eutrophication and the increasing strive towards a climate-neutral continent will lead to an increase in offshore renewable energy, causing competition for space and impacts on the seascape as well as on marine habitats and life. Hence, a holistic and integrated assessment of ES across terrestrial, coastal, and marine ecosystems is urgently needed. Furthermore, EU environmental policies are often not restricted to one side of the shoreline. For instance, the Habitats Directive (92/43/EC) (HD) aims to protect a wide range of terrestrial, coastal, and marine species and habitats [11], the WFD promotes the protection of inland surface, transitional, coastal, and groundwater [12], and the Maritime Spatial Planning (MSP) Directive (2014/89/EU) requires member states to take into account land-sea interactions [13]. Thus, a joint spatial assessment approach for land and sea is inevitable for supporting the practical application of the ES concept in EU policy implementation. Few examples of joint assessments exist, but they are often conducted on a global or European scale (e.g., [14]) or focus on a small number of ES. In order to support EU environmental policy implementation, joint approaches for the national and sub-national scale are needed that cover a variety of ES. The ES matrix approach [15], which links geospatial units (e.g., biotope or land-use/land-cover types) with ES, has been widely applied to map and assess ES in a large variety of case studies all around the globe, ranging from the local to the continental scale [16].