**5. Conclusions**

High-resolution aerial images of Bora Bora obtained from 1955 to 2019 highlighted the extensive coastal urbanisation undergone by the island since the mid-20th century. While quays and embankments were scarce in the 1950s, they represent 61% of the shoreline nowadays. This transition away from natural shorelines is accompanied by modified sedimentary regimes, and results in enhanced coastal erosion. In the context of climate change and increasing demographic pressure, preserving shoreline stability on small Pacific islands, where most constructions are located within meters of the sea, is crucial for livelihoods. The long-term impact of coastal modifications on erosional processes on Bora Bora indicated by the aerial imagery series highlight the need for proactive local management, with the removal of embankments and restoration of natural shoreline types, notably of vegetation possessing robust root systems capable of stabilising sediments.

**Author Contributions:** Conceptualization, E.G., A.C., D.J. and D.L.; formal analysis, E.G.; funding acquisition, D.L.; investigation, E.G.; methodology, E.G., A.C., D.J. and F.D.; resources, T.M., Y.R. and L.L.; software, A.C. and D.J.; supervision, A.C., D.J. and D.L.; validation, A.C., D.J., T.M., Y.R., L.L. and D.L.; writing—original draft, E.G.; writing—review and editing, E.G., A.C., F.D., M.J. and D.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has received several grants: Fondation de France (2019-08602), Ministère de l'Economie verte et du domaine-Délégation à la recherche de Polynésie française (contrat N3622 MED-EPHE), Office Français de la Biodiversité (AFB/2019/385-OFB.20.0888), Polynésienne des Eaux, ANR-19-CE34-0006-Manini, ANR-19-CE14-0010-SENSO, the Rahui Forum and Ressource Center ¯ supported by Bloomberg's Philanthropy.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are openly available in FigShare at doi.org/10.6084/m9.figshare.17048672.

**Acknowledgments:** We would like to thank the staff of Section Cadastre-Topographie de la direction des affaires foncières (DAF) de Polynésie-Française for providing the satellite images, as well as the staff of 'Polynésienne des Eaux' and of the Mairie of Bora Bora for their help in the field. We also thank the Earth and Biodiversity Science Graduate Program of PSL Université Paris (PG EABIS).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

