Multidecadal morphodynamic evolution of mangrove-fringed shorelines in Karawang, Indonesia

Purpose Mangrove-fringed muddy coasts along the Java Sea provide critical coastal protection but are increasingly stressed by relative sea-level rise, subsidence and human modification. This study quantifies multidecadal shoreline and mangrove dynamics along the 84-km coast of Karawang, north Java, Indonesia (1995–2025), and identifies coastal segments where mangrove-based measures can most effectively support nature-based coastal protection. Methods We derived shoreline change from a distance–area shift (DAS) workflow in Google Earth Engine that mimics Digital Shoreline Analysis System (DSAS) transect statistics, estimating net shoreline movement (NSM), end-point rate (EPR) and a coastal shoreline position (CSP) index at 250-m segments within a 1-km coastal strip. Mangrove extent and structural density were mapped by adapting a mangrove vegetation index (vE3) and classifying sparse, moderate and dense canopies calibrated against recent high-resolution mapping. Time series of NDVI, NDMI and MNDWI were used to characterise vegetation condition and open-water dynamics and to assess their coupling with shoreline indicators. Results The shoreline is predominantly erosive, with mean EPR reaching about − 53 m yr⁻¹ in central sectors, while western cells remain weakly accretional (up to + 9 m yr⁻¹). Mangrove area and density show contrasting trajectories among sub-districts, ranging from sustained degradation to partial recovery and landward migration. At the coast-wide scale, shoreline–mangrove correlations are weak, but several districts exhibit strong negative coupling (r down to ≈ − 0.93), where pronounced abrasion coincides with mangrove loss and expanding water area. Conclusion Integrating shoreline metrics, mangrove density, and spectral proxies delineates three morphodynamic–ecological domains with distinct retreat regimes and management implications. Domain 1 (Tempuran–Tirtajaya) combines sustained retreat (EPR ≈ − 12.3 and − 6.9 m yr⁻¹) with steady mangrove recovery, consistent with nature-based protection potential. Domain 2 (Cilamaya Kulon–Cilebar) experiences extreme retreat (EPR ≈ − 53.4 and − 16.2 m yr⁻¹) but still shows partial mangrove rebound; across the full coast, dense mangrove cover increases by ~ 105 ha, supporting a targeted hybrid strategy in the most exposed sectors. Domain 3 reflects moderate abrasion/local accretion with weak or degrading mangrove trends, indicating where more transformative planning is required. These findings provide an evidence base for mangrove conservation, rehabilitation prioritization, and adaptive coastal management in dynamically evolving tropical shorelines.