Seabed mapping: critical needs and potential application in China offshore

China has an 18,000 km continental coastline, more than 6500 islands and the marginal seas have wide continental shelves. In addition, large rivers such as the Yellow River, Yangtze River and Pearl River, and other small rivers, discharge around 1.39x109 tons of suspended sediment into the China Sea making the coast and continental shelf a prime fishery and host a variety of ecosystems. Anthropogenic impacts, including through fishing activities, have dramatically changed the Chinese coastal and offshore ecosystem in the last 50 years. Trawlers used in offshore benthic fishing, affect the seabed surface and as a result the recovery of the benthic ecosystem is under threat. It is estimated that sea-grass coverage has decreased by over half, the dominant benthic species has changed and biomass has decreased even though the biodiversity has stayed relatively stable. China has setup sixty-nine state marine natural reserves and forty-five marine special reserves during the past thirty years and most of them focus on the ecosystem protection. Artificial reefs were deployed to help the rehabilitation of benthic biomass near the coast and islands, although the practices need further assessment for better implementation in the future. The China Geological Survey is conducting a coastal and offshore mapping program intended to support the development of coastal and offshore resources and environment protection, including ecosystem assessment and recovery. Seabed mapping combining geological and biological methodologies should be taken into account, especially in those areas with intensive anthropogenic activities, such as fishing, land reclamation, and coastal and seabed engineering projects. The East China Sea coast and offshore areas are a key study area for geological and biological seabed mapping, and also face the challenge of high turbidity of sediments in the water column. Suitable seabed mapping tools and technologies need to be selected and implemented in the offshore mapping project. The interpretation and knowledge transfer to society beyond geology should also be implemented in the future.