change, rising sea temperatures and eutrophication caused by increased nitrogen pollution (Zhang et al ., 2019)
Coastal areas in the Yellow Sea are threatened by the invasive Cordgrass ( Spartina sp. ), a group of grasses native to Atlantic, European and African coasts. Spartina species have been introduced intentionally and unintentionally to many coastal areas globally. Spartina occupies large areas of open tidal flats and can facilitate the accumulation of sediment (Crooks, 2002; Civille et al ., 2005). Spartina can be detrimental to shorebirds, making tidal flats and salt marshes inaccessible (Gan et al. , 2009; Jackson et al. , 2021; Lyu et al. , 2023), as well as by reducing the diversity of benthic macroinvertebrates. Research from the Wadden Sea and Australia shows that the diversity of arthropods and macrobenthos is higher in open tidal flat and native salt marsh than in Spartina -invaded marshes (Tang & Kristensen, 2010; Cutajar et al. , 2012). Spartina can outcompete native plants, including Zostera (Madden et al. , 1993), Suaeda (An et al. , 2007), Phragmites australis , and Scirpus mariqueter (Li et al. , 2022), decreasing the amount of food resources and nesting habitats for birds. The loss of intertidal benthic fauna, such as shellfish, can negatively impact human livelihoods (Gan et al. , 2010; Goss-Custard & Moser, 1988; Jackson et al. , 2021). Spartina is a well-known invasive, but it is not the only species to cause problems in intertidal habitats. For example, Black Swans ( Cygnus atratus ) are increasing in numbers in at least two coastal national nature reserves: Yellow River Delta and Chongming Dongtan (David Melville, pers. comm.). The coastline of the Yellow Sea is a critical area for migrating birds and their reliance on this habitat as a migration stop over is a major cause of their decline (Studds et al. , 2017). The East Asian-Australian Flyway (EAAF) is a major bird migration route, where birds travel from Russia, China and Alaska to South East Asia, Australia and New Zealand. The Yellow Sea stopover accounts for around 40% of the birds travelling on the EAAF, with a yearly influx of around 3 million individual birds (Studds et al. , 2017). It is a critical staging region where the birds stop to feed and refuel while they prepare for next steps in their long-haul migration flight. In response to human population growth, many coastal areas have been converted to aquaculture ponds for food production (Sun et al. , 2015), with China being the leading aquaculture producer in the world (FAO, 2020). Although artificial, aquaculture ponds can in fact provide roosting and foraging sites for shorebirds, depending on how they are managed (e.g. Bohai Bay in China, Lei et al. 2018). Therefore, integrating waterbird conservation with economic productivity is something to be considered (Ma et al. , 2010). A healthy intertidal zone will benefit both birds and commercially important benthos. Overall, the coastal ecosystems in the Yellow Sea ecoregion, and the species within, are under immense anthropogenic pressure. In 2018, China introduced strict regulations on land reclamation, whereby general land reclamation projects will no longer be approved (Miao & Xue 2021). In South Korea, opposition by citizens has had some success, for example a lawsuit by environmental groups was brought against the Saemangeum Reclamation Project, forcing the development to take the environment into account (Koh & de Jonge 2014; Song et al. , 2014). According to IUCN (2023), despite efforts to strengthen protection for habitats in the Yellow Sea, most especially in the intertidal zone, the trends for most species continue to decline (IUCN, 2023).
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