## 4 Discussion
### Expert- and Stakeholder-Based ESA Approach  
Several studies have already shown that ecosystem service assessments can support stakeholder communication and policy implementation [29; 30]. In our case, it can serve as a tool to visualize potential benefits and trade-offs and analyze patterns and processes at a regional level [25; 42; 48]. Our results have shown that, based on the stakeholder background, different assessment strategies can be beneficial. In the case of the expert-based assessment, the web-based assessment with the option to visualize the results in real time enabled new discussion strategies and could accelerate the duration of the assessment compared with the basic paper-based assessment. This was very well demonstrated when comparing the results from the conducted ESA in Denmark and Lithuania. The experts in Denmark, who were already familiar with the topic of mussel cultivation, still showed higher deviations for the impacts of a commercial mussel farm scenario compared with a quite similar IMTA scenario (Table 6), whereas the experts in Lithuania, consisting of scientists with a general background in marine science, showed only a little deviation, comparing the effects of two very contrasting scenarios (Table 7). Here, the chosen discussion strategy, which was to conduct the discussion after the assessment, seemed to not be beneficial. Both expert groups agreed that a mussel farm which could run on a commercial level could benefit the selected provisioning, regulating, and cultural ESs around the mussel farm. Both groups mostly agreed on whether the scenario described would lead to an improvement or deterioration of the ES being assessed (Table 5). However, the degree of change differed in most cases. Some exceptions were the ESs \"Oxygen provisioning\" and \"Burial of nutrients and organic matter\", which mirrors the general risks of mussel cultivation [21; 49]. In both cases, the experts in Lithuania assessed a decline in the ESs, while the experts in Denmark determined a positive change. The differences in ratings can be attributed to a possible different understanding rather than that the scenarios were assessed in different systems (Skive Fjord, Denmark and Curonian Lagoon, Lithuania). Both systems are shallow and eutrophic [25; 50]. While the experts in Lithuania possibly saw the overall threat of bio deposition and increasing dissolved nutrients [21; 49], the experts in Denmark saw the benefits for the environment if a mussel mitigation farm acted as a nutrient sink [49; 50]. While an ESA is appropriate for expert consultations, it does not seem to be usable for non-experts (e.g., local actors (governmental, non-governmental, or business actors)), since the number and description of ESs are too specific, and it would be too time-consuming to carry out [25]. Therefore, we tested a slimmed down version with reduced services (Table 8). Striking was that the results showed that the stakeholders rated the simplified ES \"Nutrient regulation\" equally for the beach mussel farm and the floating wetlands (Table 8). Here, the perception of the nutrient regulation capacity could be biased based on the scenario provided to the stakeholders. A floating macrophyte island of 1 ha would theoretically be able to remove a similar amount of phosphorus and nitrogen compared to a mussel farm of the same size. However, floating islands could never realistically be that large due to the negative shading effect on submerged vegetation. More than their impact on nutrient regulation, the stakeholders appreciated their potential role as biodiversity hotspots and a habitat for birds, insects, and aquatic fauna [51; 52]. Those aspects seem more promising than their use purely for nutrient removal in eutrophicated waters, where the size limits the efficiency. This was also a debated topic during the discussions after the assessments. A common disadvantage of the ESA is that the stakeholders have to evaluate prefabricated scenarios whose location is already determined.