A team of marine scientists from Guangxi University has announced a significant advancement in coral conservation, coinciding with World Oceans Day, taking place on June 8. The team has successfully mastered technology that triggers large-scale coral spawning in high-latitude regions, particularly off the coast of Weizhou Island in South China's Guangxi Zhuang autonomous region.

With this pioneering technique, researchers have initiated controlled sexual reproduction of corals, a crucial development that aims to transform Weizhou Island into a sanctuary for coral species increasingly threatened by the impacts of global climate change.

Huang Wen, an associate professor at the School of Marine Sciences at Guangxi University, noted the progress as a transformative shift from merely planting corals to actively breeding them, which is essential for fostering robust underwater ecosystems.

Coral reefs, often referred to as the "tropical rainforests of the ocean," make up a mere 0.2 percent of the ocean floor, yet they provide a habitat for over 25 percent of all marine species.

The decline of coral reefs due to global warming, pollution, and other anthropogenic factors has been alarming, with regions like Weizhou Island experiencing a dramatic drop in coral cover from 60 percent in the 1980s to less than 5 percent by 2015.

In response to this environmental crisis, the Guangxi University team initiated restoration efforts in 2015. Their diverse approach included cultivating coral colonies in laboratories, recovering fragments from the ocean floor, and using seed trays to anchor them before divers relocated them to the seabed.

Within their 2,000-square-meter restoration zone, coral cover has risen significantly—quadrupling from 5 percent to 20 percent in just three years.

To date, the initiative has seen the installation of 1,520 artificial reefs, the transplantation of over 80,000 coral colonies, and the restoration of 30 hectares of reef area.

Despite these successes, researchers emphasized that coral planting by itself is insufficient for long-term restoration.

Gong Sanqiang, also an associate professor at the School of Marine Sciences, stated that natural reproduction is vital for restoration efforts to be truly effective.

Sexual reproduction enhances genetic diversity among coral populations, which is crucial for their resilience against environmental stresses.

Coral spawning is typically a brief occurrence, lasting mere hours each year.

To optimize their chances of capturing this event, scientists developed methodologies to determine spawning windows by observing the gonadal development of corals alongside environmental conditions.

This year, the team identified a 72-hour "golden window" for spawning in mid-May, leading to successful underwater observations, where divers recorded large clusters of pink reproductive bundles being released by the corals.

In an effort to maximize the spawning potential, researchers activated a water flow control system and employed specialized techniques to induce spawning, successfully collecting substantial quantities of eggs and sperm.

In the laboratory, these gametes were carefully separated and preserved in liquid nitrogen.

This approach confirms that the restored corals have reached sexual maturity and possess the capability for mass reproduction, crucial for repopulating affected areas.

Now, the liquid nitrogen tanks in the laboratory store reproductive cells from various coral populations, which team leader Yu Kefu has referred to as a "Noah's Ark" for corals, deeming them essential for future conservation and restoration initiatives.