Karst Landscapes on Yongxing Island and Shidao Island in the South China Sea

Yongxing Island is the largest island of the Xisha Islands group and is also the largest island in the South China Sea. It is China’s most important karst landform associated with coral reef islands. It has an east-west length of approximately 1,850 m, a north-south width of approximately 1,160 m and an area of approximately 2.1 km². Shidao (Shi Island) lies 1,130 m northeast of Yongxing Island on the same atoll. At low tide, Shidao is accessible to Yongxing Island by foot. Shidao is the only rocky island in the early stage of diagenesis. It has an area of approximately 0.08 km², and the highest point is 15.9 m above sea level, which is also the highest point on the Xisha Islands. It is mainly composed of bioclastic limestone that is subject to strong karst dissolution and marine erosion. Reef caves are common near the ocean surface. A 3-m-high piece of coral reef stands upright and looks like a dissected aged loofah melon with pulp. A unique karst landform, solubilisation tubes...