This study provides an in-depth understanding of the islands and sandbars within the Xisha Islands, located in the South China Sea, with the aim of distinguishing them based on different geological, ecological, and historical features. The changes in the marine ecosystem and the conservation measures taken to maintain the rich biodiversity of the archipelago are also explored. The main objective of this study was to differentiate islands and sandbars based on geological, ecological, and historical criteria and to examine the period of formation, geological features, and altitudinal characteristics of these terrains. The dynamic characteristics of sandbars were explored as the basis of island formation by focusing on their sensitivity to external environmental factors and assessing the presence of vegetation and human activities. The overall implications of these findings for marine life and conservation efforts on the Paracel Islands were analyzed. To achieve these objectives, geological investigations, historical documentation, and ecological assessments were combined. Key methods included geochronological analysis to date the formation of the islands and sandbars, assessment of elevation and geological composition to analyze the vegetation cover on these terrains, and a review of the historical documentary record to gain insights into human activities and investigate the marine ecosystem and its biodiversity. The geological studies revealed that islands are usually formed over a long period of time (approximately 4,000 years or more) and above the water surface, with beach rocks formed around them and a large amount of coral detritus accumulating on the embankment, which in turn forms a sand dike encompassing the dyke and the coastline. This protects the embankment and coastline, making the island expand in size, increase in elevation slowly and become more stable, and the landscape less susceptible to deformation. In contrast, sandbars are relatively young (within the last 3,000 years) and low in elevation, are often inundated at high tides, and are more dynamic, including accretion and erosion, making them vulnerable to environmental changes. Vegetation grows on these islands and sandbars and planted vegetation is a prominent feature. Increased vegetation cover enhances the stability, height, and area of these terrains and plays a vital role in ecological conservation. This study also presents findings on the overall declining trend in marine organisms such as corals, sea turtles, and seabirds in the Xisha Islands, the causes of which are mainly related to anthropogenic (e. g., fishing) and natural (e. g., climatic causes such as typhoons and biological causes such as reduction in food availability) factors. In addition, the Government of Sansha Municipality (a special administrative region overseeing the Xisha Islands) in China has implemented the following measures: artificially cultivating marine plants, setting up marine life protection stations, establishing marine life nature reserves, and stepping up the fight against illegal hunting, which are examples of a series of effective measures that emphasize the need to strengthen comprehensive conservation measures in the face of increasingly severe environmental challenges. This study helps understand the geological and ecological characteristics of the Xisha Islands and provides an important reference for ongoing marine conservation efforts. This methodology for distinguishing between islands and sandbars based on different criteria lays the foundation for further research on biodiversity and environmental changes in the area. In addition, this study highlights the importance of maintaining fragile ecosystems in the face of mounting environmental challenges. Overall, this comprehensive study of the islands and sandbars of the Paracel Islands highlights the dynamic nature of these terrains, the influence of vegetation on their stability, and the need to strengthen integrated measures for marine conservation efforts in the South China Sea. [ABSTRACT FROM AUTHOR]