JAKARTA - China has identified its first coral reef blue hole in the lagoon of Huangyan Island, South China Sea. A blue hole is a natural sea hole that appears to be a deep blue because it is deeper than the surrounding waters.
Launching a report by China Daily, quoted Thursday, June 25, a 2025 survey report released by the Chinese Ministry of Ecology and Environment said more than 2,700 marine species were recorded in the waters around the blue hole. Identification was carried out with environmental DNA technology.
Environmental DNA is the genetic footprint of living things left behind in water, soil, or air. From a seawater sample, researchers can read the presence of various organisms without having to capture one at a time.
The blue hole was first observed by a scientific survey team in August 2025. Initial geochronological studies, a method for estimating the age of rocks or landscapes, indicate that the sea hole was formed at least 3,200 years ago.
Blue hole in the sea is generally divided into two types. There are those formed due to the dissolution of limestone. There are also those that arise from the growth of coral reefs. This second type is considered rare in the world.
The blue hole in Huangyan is located in a dense patch coral reef area. The area of the opening reaches 1,491.7 square meters. The maximum diameter is 56.3 meters, with a depth of 16.6 meters. The inside is shaped like a funnel.
The area is home to various coral reef communities, including corals, giant clams, fish, sponges, and sea anemones. Green turtles, a Class I protected animal in China, are also observed living in the blue hole area.
Field surveys over two years recorded 165 species of hard coral from 14 families and 44 genera. Researchers also found 184 fish species from 27 families and 85 genera.
According to a China Daily report, the use of environmental DNA plays a major role in mapping the marine biodiversity in the region. These findings show the importance of technology-based surveys to recognize and maintain coral reef ecosystems.
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