QINGDAO -- The scientific research vessel Ocean One returned to a harbor in East China on Dec 28 after successfully completing a landmark marine exploration and research mission in Nigeria.

The arrival of the ship in Qingdao of Shandong province marked the completion of the country's 26th marine expedition.

The expedition included a nine-day joint cruise conducted in Nigerian waters with Chinese and Nigerian scientists, marking the first time for a Chinese research team to lead an operation in an African country's exclusive economic zone.

"It is a groundbreaking voyage in terms of boosting marine cooperation between the two countries," said Li Bo, an official with the China Ocean Mineral Resources R&D Association, organizer of the expedition.

The mission will help both sides better understand the underwater landscape and fishery conditions in the area, Captain Cao Yezheng said previously.

The expedition started in April. After setting sail from Sanya in south China's Hainan province, the ship sailed 38,000 nautical miles through the Atlantic Ocean, the Indian Ocean and the Gulf of Guinea.

The 245-day voyage allowed researchers to study biological diversity in hydrothermal areas in the Atlantic Ocean for the first time, which will provide valuable information for future biological and geological studies, chief expedition scientist Tao Chunhui said.

The Ocean One is China's only open-ocean vessel designated and equipped for deep sea research.