A systematic review reveals a scale and directionality typology of threats to coastal wetlands

Background Coastal wetlands are among the world's most rapidly declining ecosystems, exposed to cumulative pressures thatfrequently originate outside their boundaries and are intensified by fragmented jurisdictions and governance misfit. Despite numerous studies reporting wetland degradation, threats are rarely examined through two governance-relevant attributes that directly condition institutional response: the scale at which threats originate and operate, and their directionality across connected ecosystems. Methods We conducted a PRISMA-guided systematic review coding 525 articles on coastal wetland threats, classifying them by scale (local to global) and directionality (internal, land-to-sea, sea-to-land) using RAMSAR threat categories. Results Three empirically grounded threat typologies emerge. First, subnational land-to-sea threats dominate in the literature, driven by catchment-scale effluents from agricultural, urban, and industrial sources. Second, local internal threats cluster around aquaculture, physical alterations (canalisation, dredging), and peri-wetland urban expansion. Third, global sea-to-land threats are led by sea-level rise and extreme events, with regional drivers closely mirroring global-scale pressures. Discussion Each typology carries distinct governance demands: local internal threats are tractable through place-based management; subnational land-to-sea pressures require watershed-coastal alignment and inter-jurisdictional coordination; and global sea-to-land drivers depend on anticipatory, cross-scale climate adaptation. This typology provides a parsimonious diagnostic of institutional fit and mismatch and motivates further research on the policy mixes and coordination mechanisms that work best under each configuration.