Editor's note: September 20 marks the fourth China's National Coral Day, aiming to call on the society to participate in the protection of marine corals and their habitats. On this day, CGTN takes you close to a group of Chinese divers dedicated to monitoring the health condition of coral reefs and protecting the ocean.

"When I looked up from the sea floor, the dispersing coral eggs looked like dazzling stars in the sky," Zhao Xintong said when recalling the first time she witnessed coral spawning. 

In the dark ocean, little pink coral eggs released floated up one by one and suddenly swarmed out.

"There are no words to describe how I felt at the time," said Zhao.

Zhao Xintong, a volunteer at the marine environmental protection organization Blue Fins, started out as a diving enthusiast, and after noticing the deteriorating marine environment, she decided to do something to protect the ocean.

Every April, she and the members of the organization dive down to the waters of Dapeng Peninsula in the city of Shenzhen in south China's Guangdong Province to monitor the condition of coral spawning, including the spawning time, water temperature and tide conditions. 

Such kind of monitoring usually takes one and a half months as the timing of coral spawning is uncertain, sometimes at the beginning of the month, sometimes at the end of the month. To make sure they do not miss the coral spawning, a team of about 30 people takes turns, with six members monitoring it each day.

Zhao explained that the monitoring is not only a record of coral health, but also a measure of the ability of coral reef ecosystems to cope with crises.

"If there are enough new organisms, then it can enhance the resilience of coral reefs against the threat of this changing environment," she said.

Coral reefs, one of the most vital ecosystems, only occupy 0.1 percent of the ocean but are home to over a quarter of all marine life. The geological formation of coral reefs protects our land from crashing waves. Also, it has the function of carbon sequestration and regulates the global climate to some extent.

However, due to climate change and human activities, such as overfishing and land-based pollution, their survival is threatened. Some corals have cracked, some have bleached, and some have died.

In 2018, the Intergovernmental Panel on Climate Change (IPCC) predicted that 70 to 90 percent of corals would be lost at the 1.5 degrees Celsius threshold, and 99 percent if temperatures rose another half-a-degree.

Thankfully, countries around the world are beginning to develop technologies to slow the loss of coral reefs. Meanwhile, more non-governmental organizations that popularize science on marine conservation are also thriving.

"If the environment improves, maybe it will be in a better state and grow faster," said Zhao.

(If you have specific expertise and want to contribute, or if you have a topic of interest that you'd like to share with us, please email us at nature@cgtn.com.)