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 a 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 on Google Earth Engine, assisted with field survey and literature search, a total of 118 010 ha of saltmarshes were delineated in coastal China in 2019. Seven typical saltmarsh species were identified, withPhragmites australis,Spartina alterniflora,andScirpus mariquateras dominant species, accounting for 95.5% of total saltmarsh extent, whileSuaeda salsa,Tamarix chinensis,Cyperus malaccensis,andSesuvium portulacastrumwere present in limited abundance. TheP. australisand exotic speciesS. alternifloragrow along almost all coastal provinces, butP. australisdominates in the north whileS. alternifloradominates in the middle part of coastal China.Suaeda salsaoccurs mainly in the north and has suffered large losses.Tamarix chinensisis abundant in Shandong province,S. mariquaterin the Yangtze River delta,C. malaccensisin Guangdong and Guangxi provinces, andS. portulacastrumin Taiwan. The exotic speciesS. alternifloraexpanded 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.