Box 1: The Yellow Sea ecoregion
The Yellow Sea is bordered by eastern China, Democratic People’s Republic of Korea (North Korea) and the Republic of Korea (South Korea). Salt marshes and tidal flats are the principal coastal ecosystems in this region (Murray et al. , 2015), yet nearly 65% of tidal flats and nearly 60% of salt marshes have been lost since the 1950s and 1980s, respectively (Murray et al. , 2014; Gu et al. , 2018). The Yellow Sea tidal flats are now considered an endangered ecosystem under the IUCN Red List of Ecosystems due to the decline in their extent, the severity of their degradation and biotic disruption (Murray et al. , 2015). Land reclamation is one of the main drivers of intertidal habitat loss in this region but existing intertidal habitats also suffer from degradation (Melville et al., 2016; Gu et al. , 2018). In South Korea, around half of the tidal flats have been embanked since the 1970s (Koh & de Jonge, 2014) and in China, the seawall stretches for 13,830 km along the coast (Luo et al. , 2015). A typical salt marsh community in North and South Korea is dominated by Phragmites communis and Suaeda japonica (Kolbek et al. , 1989; Ihm et al. , 2001; Chung et al. , 2021), while in China the most extensive species are Suaeda salsa, Phragmites australis, Aeluropus littoralis, Zoysia maerostachys and Imperata cylindrica (Yang & Chen, 1995). However, there is evidence to suggest that reclamation and embanking could change the distribution of vegetation from a zonal pattern to a mosaic pattern by altering the salinity gradient (Feng et al. , 2018). Now, in parts of the Yellow Sea, there is next to no salt marsh, even in areas where a tidal flat remains (Melville et al. , 2016).
The Saemangeum Seawall on the southwest coast of South Korea separates the former Saegmangeum estuary from the Yellow Sea. Its construction caused controversy and opposition from some citizens and environmental groups. [Credit: Ju Yung Ki, www.grida.no/resources/4415].
The damming of both the Yellow and Yangtze rivers has drastically reduced the sediment supply to the coastline (Yang et al. , 2006; Wang et al. , 2012). Water use for irrigation and human consumption in the upper reaches of the Yellow River has also considerably reduced the fresh water flow to its delta (Yang et al. , 2020). Coastal groundwater extraction is associated with subsidence of up to 25 cm/year (Higgins et al. , 2013). In China, sewage disposal and the movement of chemical industries to the coast increases the risk of chemical pollution (Melville 2018). There are also huge outbreaks of macroalgae (e.g. Ulva prolifera ) in China and South Korea, thought to be a result of multiple factors, including climate
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