An ecosystem service assessment tool for coastal protection and restoration solutions using focus groups: Development, application, and critical evaluation

Coastal areas are under increasing pressure from human activities, threatening Ecosystem Services (ESs) and making Ecosystem-based Management (EBM) a pressing challenge for coastal populations. Nature-based Solutions (NbS) can enhance coastal protection and/or restoration while supporting EBM goals; however, purely nature-based approaches are often unfeasible and require integration with technical infrastructures, giving rise to hybrid blue-grey infrastructures. Yet, no standardized tool has been validated across this full spectrum (i.e., grey infrastructures, hybrid blue-grey infrastructures, and NbS), leaving coastal planners without a flexible, evidence-based instrument for comparing co-benefit profiles across solution types. This study applies an Ecosystem Service Assessment (ESA) tool using focus groups across nine coastal protection and/or restoration case studies situated in three regional seas (Baltic Sea, Mediterranean Sea, Bay of Bengal). Seventeen expert and non-expert participants assessed the relative importance and provision of 30 ESs (10 provisioning, 10 regulating and maintenance, 10 cultural) using a standardized, scenario-based protocol. Results show a clear and consistent gradient in ES provision across solution types, with NbS generating the highest overall co-benefit scores. Cultural services emerged as the most differentiating dimension, with NbS scoring nearly three times higher than grey infrastructures, while regulating and maintenance services (particularly control of erosion rates) remained highly relevant across all solution types. Expert and non-expert assessments showed convergent trends despite differences in absolute scores, with only one ES differing significantly after Bonferroni correction. The two non-European case studies achieved among the highest overall ES provision scores, supporting the tool’s generalizability beyond its original Baltic Sea context. These findings demonstrate that ESA by focus groups can generate robust, solution-specific evidence across the grey-to-NbS spectrum, supporting its integration within structured coastal planning frameworks such as the Systems Approach Framework (SAF).