Areal Extent, Species Composition, and Spatial Distribution of Coastal Saltmarshes in China

Coastal saltmarshes are key ecosystems with important ecological functions. Yet, they have experienced widespread decline. Due to their importance, the conservation and restoration of saltmarshes are globally-shared objectives, including China. Despite multiple local studies, nationwide information about saltmarshes in China is scarce. Thus, we used remote sensing to delineate the spatial distribution and areal extent of saltmarshes along coastal China, and resolve their species composition. By interpreting 10 m spatial resolution Sentinel 2 images in Google Earth Engine, assisted with field survey and literature search, totally 118,010 ha of saltmarshes were delineated in coastal China in 2019. Seven typical saltmarsh species were identified, with Phragmites australis, Spartina alterniflora and Scirpus mariquater as dominant species, accounting for 95.5% of total saltmarsh extent, while Suaeda salsa, Tamarix chinensis, Cyperus malaccensis and Sesuvium portulacastrum were present in limited abundance. The P. australis and exotic species S. alterniflora grow along almost all coastal provinces, but P. australis dominates in the north while S. alterniflora dominates in the middle part of coastal China. Suaeda salsa occurs mainly in the north and has suffered large losses. Tamarix chinensis is abundant in Shandong province, S. mariquater in the Yangtze River delta, C. malaccensis in Guangdong and Guangxi provinces, and S. portulacastrum in Taiwan. The exotic species S. alterniflora expanded extensively along the coast and its expansion rate continues to increase. The results provided conform a much-needed baseline for future monitoring efforts and the assessment of progress in the conservation and restoration projects toward recovering saltmarshes in China.