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This paper provides new insights on the impacts of a category 5 tropical cyclone on Indian Ocean atoll reef islands. Using multi-date aerial imagery and field observations, the contribution of tropical cyclone Fantala to shoreline and island change, and to sediment production and transport, was assessed on Farquhar Atoll, Seychelles Islands. Results show that the two largest islands (> 3 km 2 ) only suffered limited land loss (− 1.19 to − 8.35%) while small islets lost 13.17 to 28.45% of their initial land area. Islands and islets exhibited contrasting responses depending on their location, topography and vegetation type. Depending on islands, the retreat of the vegetation line occurred either along all shorelines, or along ocean shoreline only. The structure (wooded vs. grassy) and origin (native vs. introduced) of the vegetation played a major role in island response. Five days after the cyclone, beach width and beach area were multiplied by 1.5 to 10, depending on the setting, and were interpreted as resulting from both sediment reworking and the supply of large amounts of fresh sediments by the reef outer slopes to the island system. Fourth months after the cyclone, extended sheets of loose sediments were still present on the reef flat and in inter-islet channels and shallow lagoon waters, indicating continuing sediment transfer to islands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper provides baseline data on absolute and relative sea level variations and shoreline changes in the Scattered Islands region of the Indian Ocean, based on aerial image analysis, satellite altimetry and field observations and in situ measurements from the 2009 and 2011 TAAF scientific expeditions. The analysis shows the importance of regular observations and monitoring of these islands to better understand reef island responses to climate stressors. We show that Grande Glorieuse Island has increased in area by 7.5 ha between 1989 and 2003, predominantly as a result of shoreline accretion: accretion occurred over 47% of shoreline length, whereas 26% was stable and 28% was eroded. Topographic transects and field observations show that the accretion is due to sediment transfer from the reef outer slopes to the reef flat and then to the beach. This accretion occurred in a context of sea level rise: sea level has risen by about 6 cm in the last twenty years and the island height is probably stable or very slowly subsiding. This island expansion during a period of rising sea level demonstrates that sea level rise is not the primary factor controlling the shoreline changes. This paper highlights the key role of non-climate factors in changes in island area, especially sediment availability and transport. We also evidence rotation of the island, underscoring the highly dynamic nature of reef islands. [ABSTRACT FROM AUTHOR]