Scientists restore fragile seabed ecology

Coral biologist Huang Hui has devoted half her life to re-creating a beautiful memory: vast stretches of colorful corals thriving on the seabed of the South China Sea. "It's stunning," says Huang, recalling her first sight of underwater paradise, off the coast of Sanya, Hainan province, in 2002. "The seabed was fully covered with colorful coral bushes, dotted with fish and shrimp of different colors and shapes."

Huang started her career in 1993 at the South China Sea Institute of Oceanology of the Chinese Academy of Sciences. In 1996, she joined the team of Zou Renlin, China's pioneer in coral taxonomy, to figure out the distribution of corals in China.

The experience in Sanya was the first and last time Huang saw thickets of corals on such a scale, as they have become more rare in recent years.

Studies show that China has lost over 80 percent of its coral reefs in the past 30 years. In the South China Sea, the coral coverage on the seabed has plunged from around 60 percent to 20 percent, and worldwide, the coral coverage has dropped to about 15 percent in recent decades.

"We have kept recording the area of corals in China. Sadly, it is shrinking every year," Huang says.

Corals are fragile animals, she says, and they prefer clear, warm and good-quality waters. "Tiny fluctuations of temperature, salinity or water quality may result in the death of large areas of corals," she adds.

Corals have important geological and ecological values. Coral reefs can help protect the seashore from erosion, and coral bushes serve as habitats for small fish, shrimp and shellfish.

To help the coral community recover, Huang decided to plant corals under the sea. In 2009, she organized a team in Sanya who bred "coral seedlings" in a nursery, and then transplanted them to the seabed. Different types of corals were chosen according to the various seabed conditions.

"We use glue and steel frames to tie corals onto the seabed. We need to remove rocks and level the seabed before planting corals," Huang says.

However, growing corals on the seafloor is not an easy job. Weather conditions are a major variable that influence coral planting.

The ideal diving conditions are when the wave height is less than a meter, she says. Higher wave heights can be dangerous, because the divers find moving around underwater difficult and the small boat can easily be blown away.

Seasickness is another challenge.

"The journey to a coral plantation area often takes four days, but it took six days last time due to the strong wind. I just lay in the bed, which moved up and down with the boat, making me feel sick," she says.

Typhoons and tropical cyclones are frequent visitors to the South China Sea. She and her team only have a small window to carry out the underwater work each year.

"If the weather permits, we make the most of the time available," Huang says. A bottle of oxygen allows about 30 minutes of diving, during which time a diver can only plant a few coral bushes.

Despite the challenges, their efforts have paid off. Since 2009, Huang and her team have planted 120,000 to 150,000 corals, covering over 200,000 square meters of seabed of the South China Sea. Yet, she considers this result to be only "a drop in the ocean".

"The underwater ecosystem needs time to recover. Planting corals is only the first step in restoring the underwater ecology. We need time to plant more," says Huang. "Hopefully, the corals will gradually become a forest, and the fish and shrimp will come back."

Now in her 50s, Huang is still repairing corals in an experimental area. She says her biggest dream is to see a mass of corals on the seabed of Sanya again.

"Coral planting is our lifelong goal. I feel happy to see seabed ecology is getting better thanks to our work," she says.

Xinhua