QINGDAO -- Carrying an oxygen tank and wearing diving goggles, Zhang Peidong, a professor at the Ocean University of China, took a deep breath and jumped into the sea. He observed the seagrass, noting updates on their growth on waterproof paper.

Zhang has maintained this routine for over 17 years. During this time, he and his team have restored more than 20,000 mu (about 1,333 hectares) of seagrass beds in China's Yellow Sea and Bohai Sea.

"I wish to plant a grassland in the sea," he said.

Seagrasses, alongside mangroves and coral reefs, are globally recognized as one of the three main marine coastal ecosystems. They play a critical role in the environment, with carbon absorption rates that can be up to 90 times higher than forests. However, due to both natural and human factors, seagrass beds along China's coasts have been in decline, resulting in a significant loss of biodiversity in shallow marine waters.

"Seagrass beds provide essential food sources for marine animals, making them as vital to marine life as grasslands are to cattle and sheep," Zhang said, emphasizing the restoration of these beds is both an urgent and important task.

UNDERSEA ENDEAVORS

To achieve his goal, Zhang's first step was to understand the growth characteristics of seagrass, an area where domestic research had been limited.

In 2008, Zhang and his team began studying seagrass at Rongcheng, East China's Shandong province. The region, known for its seasonal swan migrations, is home to eelgrass, a key species in China's temperate waters. Eelgrass serves as an important food source for swans during winter, helping protect the local marine ecosystem.

"When does eelgrass bloom and set seeds? At what time do the seeds fall off? And when do they sprout?" Zhang asked. "We conducted many underwater investigations and experiments." This process took nearly a decade.

To gather data, Zhang and his team learned to dive. They often worked late into the night, sailing to collect samples at low tide and returning at dawn. In winter, they chiseled through ice to dive into frigid waters.

"Every team member carries a small bottle of spirit to take a sip before diving in. The brief warmth helps fight off the cold," Zhang said.

After 10 years of meticulous study, the team developed a clear understanding of eelgrass ecology, clarifying its growth patterns and ideal environment. This knowledge formed the foundation for their restoration efforts.

SEAGRASS RESTORATION

Building on their earlier research, Zhang and his team sought to accelerate the restoration process through artificial methods and significantly enhance the restoration effect.

Seagrasses reproduce differently from other marine plants. As higher plants, they can be propagated either by seeds or through transplantation.

Every June, the team collects eelgrass seedlings, which are then propagated in a light-permeable nursery for nearly three months. Propagation requires finding the most effective way to adjust the water's nutrient levels, a process that can be exhausting in temperatures over 40 degrees Celsius. By mid-September, the propagated seedlings are transplanted back onto the seabed.

In addition to transplanting, the team has explored direct seeding methods to enhance the restoration process. They discovered that, under natural conditions, eelgrass seeds have a very low survival rate due to ocean currents and grazing.

To increase seed survival, Zhang's team developed innovative techniques, such as sacking seeds, wrapping them in gauze, and encasing them in mud. These methods significantly boosted the survival rates of the seeds.

TECH INNOVATION

Zhang's team also pioneered a technological innovation to improve planting efficiency. They developed an unmanned seeding boat -- a small, motorboat-like vessel with eight holes for dispersing seeds.

Previously, seeding required direct contact with the sea, a process that was labor-intensive and inefficient. Peng Liye, one of Zhang's students, was inspired by aerial seeding techniques used on land and proposed a similar method for the sea.

"We designed a boat that can be remotely controlled from the shore to evenly disperse seeds," Peng explained. "This allows us to save time and avoid the task of going into the sea."

The team also developed other innovative tools such as plant insertion machines and seedling clamping devices, which have improved work efficiency by several times.

So far, the team has carried out China's first large-scale seagrass bed restoration projects, including those in Tangshan, North China's Hebei province, Weihai, Yantai and Dongying in Shandong province, yielding significant ecological and social benefits.

In 2022, they led the creation of China's first industry standard for seagrass bed restoration, providing a technical foundation for future restoration projects.

"Seagrass protection and restoration have become an integral part of my life," Zhang said. "Watching the seagrass take root and grow, one by one, brings vitality and hope to the ocean. This is the reason we persevere."