Assessing Coastal Marshes Ecosystem Services: A Systematic Review of Ecological Indicators

Coastal marshes are heterogeneous habitats that provide multiple ecosystem services (ES) but have suffered major declines on the global scale. Therefore, the conservation and restoration of marshes are pivotal for biodiversity maintenance and climate change mitigation and adaptation. However, the evaluation of their effectiveness to tackle environmental challenges depends on ES assessments grounded in ecological indicators, for which comprehensive, updated overviews are lacking. We systematically reviewed the ecological literature to identify the temporal evolution of coastal marsh ES assessments, along with the diversity and operationalization of ecological indicators. We found that studies on coastal marsh ES have grown since 2009, with a predominance of research on Climate Regulation, Bioremediation and Water Purification, and Coastal Protection-related services. Most studies focused on a single service, overlooking potential synergies and trade-offs among ES. Furthermore, few ecological studies evaluated social or economic benefits, indicating challenges in effectively communicating human reliance on coastal marshes. The number and type of ecological indicators varied across services. A high diversity of indicators reflected both the maturity of certain ES and a lack of standardized metrics, indicating that methodological consistency and ecological comprehensiveness remain a challenge. We highlight that multivariate approaches, assessing multiple ES by using bundles of complementary indicators, will enable more informative assessments. This study provides guidance for selecting appropriate ecological indicators and underscores the need to integrate ecological, social, and economic dimensions of coastal marsh ES to better support management and policy strategies.