Priority areas for wintering waterbirds and the need to remove Spartina along Zhejiang coast

Abstract

The East Asian-Australasian Flyway (EAAF) is home to over 50 million migratory waterbirds, of which 32 are globally threatened and 19 are near-threatened. These migratory waterbirds rely on productive coastal wetlands to rest and feed, allowing them to replenish their energy reserves for their next leg of migration. The Zhejiang coast, an important wintering and stopover site for migratory waterbirds in the EAAF, has undergone marked changes in recent decades, including alterations to its habitat owing to reclamation activities. The temporal and spatial dynamics and community diversity of waterbirds in this coastal area as well as the places that require increased attention for protection remain poorly understood. Therefore, in the current study, we aimed to elucidate the diversity and community structure of waterbirds in diverse coastal wetlands within Zhejiang. Based on synchronous survey data collected during the wintering period from 2022 to 2024 in Zhejiang, the taxonomic, phylogenetic, and functional diversity of four groups of waterbirds (dabbling birds, diving birds, large waders, and small waders) across 10 main coastal wetlands in Zhejiang were assessed. The results showed an increased abundance of dabbling birds, and small waders experienced a significant decrease in recent years. As integral components of the EAAF, three regions (Hangzhou Bay, Wenzhou region, and Xuanmen-Yueqing Bay) within Zhejiang should be considered high priority because of the three criteria of critical international wetlands, the irreplaceability index, and the critical position within the community structure. An analysis of community structures revealed that environmental factors were crucial in shaping dabbling birds and large wader communities. These findings were supported by constrained principal coordinate analysis, which suggested that the percentage of the cordgrass Spartina alterniflora is a factor influencing these phenomena. The geographic location and percentage of S. alterniflora might have contributed to these differences. These results were consistent with the S. alterniflora removal work by the government. Overall, these findings have important implications for policy-making decisions regarding species conservation efforts along the East-South China coast. Effective measures should be implemented to restore vegetation in tidal wetlands along the coast to provide suitable habitats for different groups of waterbirds. Further development and utilization, including the economic exploitation and management of these crucial coastal wetlands, as well as the management of wetland vegetation, should be approached with greater caution.