Abstract: Coral sand islands are common geomorphic features in tropical oceans, holding significant ecological functions and scientific value. However, intensified global climate change and increased human activities in recent years have posed severe challenges to their stability and ecological environments. This study focuses on North Island, a representative coral sand island in the Xisha Islands of the South China Sea. Using high-resolution remote sensing imagery from 2002 to 2023 and digital shoreline analysis system（DSAS), we examined shoreline dynamics and beachrock degradation on North Island. The study further explored the driving factors of island evolution and proposed targeted protection strategies. The results indicate that: (1) The length and area of North Island's shoreline initially increased and then declined, reaching their maximum in 2019. From 2015 to 2019, land reclamation significantly expanded the shoreline, while from 2019 to 2023, severe erosion occurred. Changes in the island's sandy spits were the most pronounced, displaying erosion under the influence of the northeast monsoon and accretion during the southwest monsoon, with seasonal variability exceeding interannual changes. Beachrock on North Island has rapidly diminished due to human interference. (2) The evolution of coral sand islands is fundamentally driven by interactions between hydrodynamics and sediment. Coastal hydrodynamic changes, coral reef degradation, global climate change, and human activities collectively drive the transformation of coral islands. (3) This study proposes a stratified ecological protection strategy, involving multilayered measures from the supratidal to subtidal zones. Techniques such as vegetation-based sand stabilization, mobile sand barriers, diamond-shaped sandbags, and beachrock restoration balance ecological conservation with island protection needs, offering practical insights for the protection and management of coral sand islands in the South China Sea.

Key words: coral sand island, remote sensing monitoring, digital shoreline analysis system, ecological protection