## 2 Study Site and Methods
### Process of the Ecosystem Service Assessment  
We used two approaches of ecosystem service assessments: a quantitative data and literature-based, subsequently called data-based, approach, and a qualitative group-based approach. For the data-based assessment, one scientist compiled data, literature, regional policy and planning documents as well as monitoring data and carried out the assessment based on this knowledge. The data collection took one to two months. The group-based assessment was carried out by a group of people with different backgrounds and expertise. The assessments took place in different groups. The single group assessments were always kept separately and later combined into a joint assessment. The Hutelmoor 1980-2040 assessment included altogether ten persons, six coastal scientists and four university students with focus on coastal environmental sciences. The choice of experts was largely opportunistic, depending on availability and readiness to carry out the assessment. For the Ahrenshoop 2020-2070 assessment, experts with a scientific and practical planning background were involved. Criteria for the expert selection were experience in ecosystem service assessments or ecosystem management, knowledge in local climate change effects and adaptation, expertise in coastal management, coastal protection or land use change, and/or knowledge in local and/or regional planning. Altogether, 22 experts complied with at least one criterion and were contacted via e-mail, 13 responded positively, and finally 9 experts participated in the assessment. The possibilities to select and involve experts were restricted because of the COVID-19 pandemic. All involved experts received an ecosystem service assessment in the form of an EXCEL table, a guideline document that included a brief overview about the aims of the  
Figure 4: Visualization of the methodological approach. assessment, characteristics of the study site and visualizations of the scenarios. The experts were asked to fill in the assessment sheet and send it back via email. The level of expertise was judged based on participants' self-assessment carried out before the ecosystem service assessment process. Criteria for the self-assessment in the Httelmoor case study were knowledge with respect to ecosystem services, the Hutelmoor, coastal realignment and wetland ecology. With respect to the Ahrenshoop case study, the criteria were knowledge in ecosystem services, local climate change impacts and spatial planning. The self-scoring scheme was 1 = low, 2 = medium and 3 = good knowledge. The individual EXCEL assessment sheets listed all ecosystem services (with explanations) in rows and all scenarios in separate columns. In a first step, participants were asked to assess the relative importance (RI) of every ecosystem service, using the classes 0 (no relevance), 1, 2, 4 and 8 (very high relevance). In a second step, every scenario was compared to the baseline scenario, representing the present situation. This was done for every ecosystem service. On a relative scale ranging from \(-4\) (very high decrease of a service) to +4 (very high increase) the participants provided their view on the extent of changes in ecosystem service provision between the baseline and the other scenarios. At the end, the participants were asked to judge the complexity, comprehensibility and visualization of the entire approach (1 = low/bad, 2 = moderate/ok, 3 = high/good) and estimate the time needed for carrying out the assessment. An assessment sheet is provided in Appendix A. The ecosystem service assessment was followed by a discussion process. In the case of Hutelmoor 1980-2040, the results were screened. Five ecosystem services did show a high variability between the expert scores. To obtain better insight into the experts' views and understand the reasons for the scores, the respective persons were contacted, and, after a brief review of the results, asked to explain the reasons behind their score.