In the South China Sea, near Huangyan Island, lies one of the most unusual natural formations discovered by marine researchers in recent years. At first glance, it resembles other known blue holes – deep, circular sinkholes surrounded by intensely blue water. However, a new study has revealed that scientists are looking at an object of a completely different nature.
Unlike most known blue holes, which formed in limestone rock thousands of years ago, the formation near Huangyan Island emerged approximately 3200 years ago as a result of coral reef growth. This is the first thoroughly studied coral blue hole, making it particularly valuable for science.
To explore this ecosystem, Chinese specialists combined several modern methods. Underwater vehicles conducted detailed photo and video surveys, 3D mapping allowed for the reconstruction of the hole's structure, and environmental DNA (eDNA) analysis helped identify animal species even from traces of genetic material they left in the water.
The results were impressive.
Researchers recorded 165 species of reef-building corals and 184 species of fish. Additionally, giant clams, anemones, and sponges were found inside and around the blue hole, along with evidence of the rare green sea turtle. eDNA analysis indicated that the actual diversity of organisms might be even higher, as not all species can be observed during direct dives.
However, the main discovery was not the number of organisms found.
Scientists gained the opportunity to trace how a complex coral ecosystem formed and persisted over several millennia. Such natural formations serve as unique archives of ocean history, allowing for the study of coral growth processes, changes in the marine environment, and mechanisms of biodiversity preservation.
Not long ago, such research was practically impossible. The depth, complex terrain, and fragility of coral communities severely limited the capabilities of traditional expeditions. Today, the situation is changing thanks to autonomous underwater vehicles, robotic systems, high-precision 3D mapping, and eDNA analysis methods. Together, they enable the exploration of marine ecosystems with high accuracy and minimal environmental impact.
The story of the Huangyan Island blue hole serves as a reminder that even in the 21st century, the ocean continues to hold places about which science knows very little. Each new study not only expands the list of known species but also helps us better understand the ecosystems on which the health of the World Ocean depends.
