China's first coral reef blue hole a biodiversity hotspot, report says

China's first identified coral reef blue hole, located in the lagoon of Huangyan Island in the South China Sea, has been recognized as a biodiversity hotspot. According to the 2025 Survey Report on the Huangyan Dao Blue Hole, released by the Ministry of Ecology and Environment on Thursday, over 2,700 marine species have been recorded in the surrounding waters using environmental DNA technology.

The blue hole was first observed by scientific survey personnel in August 2025. Preliminary geochronological studies suggested it was formed at least 3,200 years ago. Marine blue holes are classified into limestone dissolution types and coral reef growth types, with the latter being rare globally.

Situated in a dense patch reef area, the blue hole features an entrance area of 1,491.7 square meters, a maximum diameter of 56.3 meters, and a depth of 16.6 meters, with a funnel-shaped internal structure. It hosts diverse coral reef communities, including corals, giant clams, fish, sponges, and sea anemones. The green sea turtle, a Class I protected species in China, has been observed inhabiting the blue hole.

Field surveys over two years have recorded 165 species of hard corals from 14 families and 44 genera, and 184 species of fish from 27 families and 85 genera.

The extensive use of environmental DNA technology has significantly contributed to identifying the marine biodiversity in this area.