Mangroves: a natural early-warning system of erosion on open muddy coasts in French Guiana

Coastal instability is not tantamount to vulnerability of mangroves everywhere but rather brings out their exceptional ecological adaptability to cope with morphosedimentary processes. This adaptability has, however, not yet been sufficiently assessed regarding its ability to provide early warning of severe risks induced by marine erosional processes for settlements built backshore of the mangroves. Here we show, using a 68-year (1950–2017) archive of aerial photographs and satellite images, how the monitoring of the fluctuations of mangrove shorelines over the last seven decades may support predictions of coastal vulnerability to erosion in French Guiana. For this example, a coastal vulnerability index of the inhabited shoreline, expressed in years, was developed from the archive of mangrove shorelines and based on estimates of annual erosion rates for each kilometer. This simple mangrove-based early-warning approach is discussed with regards to enhanced observational and modeling considerations of oceanic forcing and sediment processes and oceanic forcing typical of ocean-facing mangrove coasts.