Drivers of shoreline change in atoll reef islands of the Tuamotu Archipelago, French Polynesia
Résumé
This paper increases by around 30% the sample of atoll reef islands studied from a shoreline change perspective,
and covers an under-studied geographical area, i.e. the French Tuamotu Archipelago. It brings new irrefutable
evidences on the persistence of reef islands over the last decades, as 77% of the 111 study islands exhibited areal
stability while 15% and 8% showed expansion and contraction, respectively. This paper also addresses a key
research gap by interpreting the major local drivers controlling recent shoreline and island change, i.e. tropical
cyclones and seasonal swells, sediment supply by coral reefs and human activities. The 1983 tropical cyclones
had contrasting impacts, depending on the shoreline indicator considered. While they generally caused a marked
retreat of the stability line, the base of the beach advanced at some locations, as a result of either sediment
reworking or fresh sediment inputs. The post-cyclone fair weather period was characterised by reversed trends
indicating island morphological readjustment. Cyclonic waves contributed to island upwards growth, which
reached up to 1 m in places, through the transfer of sediments up onto the island surface. However, the steep
outer slopes of atolls limited sediment transfers to the reef flat and island system. We found that 57% of the study
islands are disturbed by human activities, including ‘rural’ and uninhabited islands. Twenty-six percent of these
islands have lost the capacity to respond to ocean-climate related pressures, including the ‘capital’ islands
concentrating atolls' population, infrastructures and economic activities, which is preoccupying under climate
change.