Pratas Island, its lagoon, and its horseshoe-shaped coral reef are the centerpiece in this southeast-looking, low-oblique photograph. Named Dongsha Island (East Sand Island) by the Chinese, Pratas is approximately 200 miles (322 kilometers) southeast of Hong Kong in the northern South China Sea. The island and its reef are the remains of coral skeletons on a submerged sea terrace now 984 feet (300 meters) below the sea surface. The island is a sanctuary for many tropical birds. The phosphorous-rich lime soils of the island mix with the abundant bird guano deposits to make excellent fertilizer that is transported by the Chinese to the mainland for agricultural use.