Coastal aquaculture and land reclamation are swallowing about 61 percent of the country's natural shorelines and up to 33 percent of its mudflats, report shows.

The shorelines and mudflats are important in preventing coastal erosion.

The report, released by the State Oceanic Administration on Friday, said more shorelines and mudflats will disappear if no effective measures are taken to protect the country's fragile coastal environment.

Guan Daoming, deputy director of the National Marine Environmental Monitoring Center, said authorities should control human activities in coastal areas because such areas are important to the marine biological system.

The maintenance of mudflats can help prevent coastal erosion, dilute pollutants and support a large population of wildlife such as mangrove forests and migratory birds, he said.

Research shows that one hectare of mudflats can purify excess nitrogen and phosphorus from 100 hectares of farmland, which is the most effective way to filter out agricultural pollution and industrial sewage.

The report also says the country's mangrove forests have been reduced to 27 percent of the level seen in the 1950s and coral reefs to 20 percent of the 1950s level.

As mudflats disappear, natural shorelines are being replaced by construction sites for villas and industrial zones.

The report said more than 70 percent of the coastlines in Liaoning, Tianjin, Hebei, Shanghai, Zhejiang and Guangxi are occupied by human development.

Construction of buildings on the shoreline, or land reclamation, will pose a threat from fluctuations in sea levels to people living on the coast.

However, construction in China's coastal areas continues to boom, playing a significant role in rapid urbanization and solving land shortages.

The report predicts that construction projects in coastal areas will continue to increase in coming years, and said the authorities must exercise strict control over land-reclamation projects.

Besides vanishing natural shorelines and mudflats, the offshore environment is generally unhealthy, Li Peiying, the report's investigation leader, said.

Latest statistics from the State Oceanic Administration show the area of severely polluted seawater increased from 25,000 square kilometers in 2003 to 44,000 sq km in 2011.

The State Oceanic Administration report took eight years to complete, involving more than 30,000 scientists and experts at a total cost of 2.3 billion yuan ($365 million).

Investigators found the seas around China have the potential to provide the country with nearly 1.6 billion kilowatts of energy generated from marine-renewable and offshore wind and wave sources, the report said.

In Daguan Island, Shandong province, a power station using marine energy can generate more than 130,000 kW a year.

wangqian@chinadaily.com.cn