Résumé
The question of the erosion of the shorelines rimming the Mekong River delta has been treated from various points of view, including the impact of anthropogenic activities, climate change, and the role of mangroves through their presence, absence, and abundance. Concerning this last point, the approaches used, whether theoretical or conceptual, have been based on limited in situ data, and this, in turn, has affected reflections on how mangroves contribute to coastal protection. The aim of this study is to examine to which extent the width of the mangrove fringe along the shoreline contributes to the trapping of sediments and to overall coastal stabilization, with the implicit commonly accepted notion that the larger the mangrove fringe, the more efficient mangroves are in protecting the shoreline against retreat. Using high-resolution satellite images, we measured the width of the mangrove fringe in 2011 and compared this to the shoreline change between 2003 and 2011 for 3687 cross-shore transects spaced 100 m apart. We then determined the statistical relationship between shoreline change and mangrove width. The results show no significant trend, a finding that differs from Phan et al. (2015) who depicted, on the basis of 18 data points, a linear relationship between reduced mangrove width (mangrove squeeze) and coastal erosion. Our study reveals a much more complex interaction, notably in the strongly eroding, dominantly muddy, and naturally mangrove-rich sector south of the multiple delta mouths and underpins the overarching role of prevailing erosion and mud redistribution by waves and currents. Mangrove stability and delta shoreline equilibrium are strongly linked to fine-grained river sediment supply, and its alongshore transport and deposition. Our study concludes that the role of mangroves in coastal protection needs to be carefully considered in a context that takes into account antecedent prevailing shoreline erosion or accretion vested in the larger-scale control exerted by alongshore adjustments between net sediment supply or availability, wave and current energy, and sediment redistribution by waves and currents. Mangrove squeeze and removal contribute to the aggravation of shoreline erosion.