Human disturbance is a primary discriminator of coastal lagoon typology in sedimentary barrier lagoons located in southern UK and France

The environmental heterogeneity of coastal lagoons makes their classification challenging. Historically, lagoons have been characterised unilaterally according to their geomorphological, hydrological, saline or biotic features. While these characteristics are important, they independently fail to capture the nuanced complexity of coastal lagoons as multistressor environments. The vulnerability of these ecologically important, but neglected, habitats to continued climate change and anthropogenic pressure remains largely undetermined because of their inadequate appraisal. A systematic approach is therefore needed to facilitate their classification and improve assessment. Here, we developed a holistic, multivariable-driven classification using 16 environmental and anthropogenic variables to characterise 37 sedimentary barrier lagoon systems across the UK and southern France. Hierarchical clustering was employed to identify clusters naturally a posteriori, without imposing a predefined number of clusters. Five distinct lagoon clusters were revealed, with human disturbance emerging as the key discriminator of lagoon typology. Hydrology, temperature and naturalness were also identified as strong predictors, while salinity showed no discriminative power. This categorisation offers a reproducible means for the assessment of coastal lagoons to facilitate and prioritise field surveys. Furthermore, it provides a baseline for evaluating the biological and ecological consequences of lagoon type, including impacts on biodiversity, water quality and individual organisms, which may support conservation prioritisation and management decision making.