Sedimentary Cells vs. DSAS: Quantifying Erosion Along the Northern Mexican Caribbean Coast

Coastal erosion is commonly assessed from shoreline-position change using methods such as the Digital Shoreline Analysis System (DSAS). However, on microtidal sandy beaches with strong seasonal wave variability, shoreline retreat may reflect temporary sediment redistribution rather than permanent erosion. This study evaluates the morphodynamic behaviour of a ~280 km sandy coastline along the Mexican Caribbean (Isla Blanca–Punta Allen) between 2009 and 2024 using high-resolution RapidEye and PlanetScope satellite imagery. Beach-area changes were quantified for 160 sedimentary cells and analysed with the Mann–Kendall test to identify long-term morphological trends, while shoreline mobility was assessed separately using the DSAS End Point Rate (EPR) and Linear Regression Rate (LRR). The results indicate that the coastline is predominantly characterised by dynamic equilibrium and seasonal sediment redistribution: 64.4% of the cells remained stable, 15.0% exhibited redistributive behaviour, and only 12.5% showed persistent beach-area loss. In contrast, the DSAS analysis based on Total EPR showed shoreline retreat (EPR < 0) in 78.1% of the cells, whereas only 12.5% showed persistent beach-area loss, indicating that shoreline-position change alone may overestimate chronic erosion along this seasonally dynamic coast. Although DSAS rates were moderately to strongly correlated with beach-area trends (r = 0.59–0.64), the two approaches led to markedly different management interpretations. These findings demonstrate that multi-temporal beach-area analysis provides a valuable complement to shoreline-based methods, enabling a clearer distinction between seasonal variability and chronic erosion on highly dynamic microtidal coasts.