Ecosystem services in shellfish reef restoration and coastal policy: A global scoping review

Shellfish reefs can contribute to nature-based solutions (NbS) that can support coastal protection, water quality, and biodiversity, yet the extent to which their ecosystem services (ES) are reflected in coastal policy remains unclear. This global scoping review maps the scientific evidence on ES associated with shellfish reefs and examines their relationships with restoration approaches, policy instruments, and governance frameworks. Specifically, we (i) classify reported ES, (ii) examine associations between restoration approaches and reported ES, (iii) assess the representation of policy instruments and governance dimensions in the reviewed literature, and (iv) identify knowledge gaps relevant to coastal management and planning. We used a predefined search strategy, eligibility criteria, and structured full-text coding to map evidence across shellfish taxa, geographic regions, restoration approaches, and policy dimensions, identifying areas of concentrated and limited representation within the retrieved literature. Within the 151 included studies, regulating and supporting services were reported more frequently than provisioning and cultural services. Although approximately three-quarters of studies included explicit policy content, links to operational instruments—such as spatial planning, permitting, and incentive-based mechanisms—were less frequently reported. Monitoring and stakeholder engagement were inconsistently documented, potentially limiting the usability of the published evidence for decision-making. These findings reveal gaps in how connections between ecosystem-service evidence, restoration, and coastal governance are documented in the literature. Greater attention to socio-ecological objectives, consistent restoration monitoring, and the reporting of links between ES outcomes and policy instruments could strengthen the relevance of this evidence for coastal decision-making. Broader documentation from less frequently represented regions, including parts of the Global South, would improve the geographic breadth of the evidence base.