Comparing different management strategies of river mouths for waterbird conservation: A case study along the Yellow Sea coast

Coastlines with extensive estuaries and broad tidal flats are acutely vulnerable to coastal development. The tidal wetlands of the Yellow Sea are globally important for waterbirds, yet river mouths have disproportionately been developed as industrial ports, fishing ports, or have become abandoned fishing ports, with the type of management strategies depending on biophysical attributes and regional economic drivers. However, river mouths also support extensive upper tidal flat ecosystems, in contrast to many open coastal regions of the Yellow Sea, where reclamation has excised many of the upper tidal flats and dramatically reduced the time that tidal flats are available for foraging and roosting waterbirds each day. However, the extent to which waterbirds disproportionately occurs in river mouths compared to the open coast in the region remains unclear. We used a paired survey design to quantify the waterbird communities and habitat attributes (i.e., areas of upper tidal flats, Spartina alterniflora, and human activity) of 15 river mouths and 15 otherwise similar adjacent open coasts areas along the Yellow Sea coast. Waterbird species richness and abundance were higher in river mouths than open coasts. Among river mouths, the most species rich waterbird communities occurred in fishing ports and the most species poor in industrial ports. Notably, upper tidal flats were absent in many of the open coast regions, which had been subject to reclamation. Our results suggest that river mouths, especially those river mouths currently used as fishing ports, are probably of crucial importance for waterbird conservation on the Jiangsu coast due to their larger areas of upper tidal flats. Our work highlights the need to ensure that the tidal flats in river mouth systems are effectively protected to promote the completion of the annual cycle of migratory waterbirds.