Changes in migratory waterbird communities and benthic resources after coastal tidal-flat photovoltaic construction: a case study of a Spartina alterniflora restoration area in Rudong, Jiangsu Province

Spartina alterniflora invasion can alter vegetation structure, sediment properties, and hydrodynamic conditions in coastal tidal flats, thereby reducing the availability of open tidal flats for migratory waterbirds. Tidal-flat photovoltaic projects are usually accompanied by S. alterniflora removal and habitat restoration; however, whether the constructed photovoltaic area can provide alternative habitats and food resources for migratory waterbirds remains unclear. In this study, the S. alterniflora management area, adjacent bare tidal flats, and photovoltaic area in Rudong, Jiangsu Province, were selected as the study area. Line-transect surveys and benthic fauna sampling were conducted to analyze changes in waterbird communities and food resource structure before and after photovoltaic construction. The results showed that the planned photovoltaic area in 2021 was mainly a mono-dominant S. alterniflora habitat, where only 16 bird species were recorded. After S. alterniflora removal and photovoltaic construction, the number of bird species in the photovoltaic area increased from 33 in 2023 to 68 in 2025, and the community composition gradually shifted toward a more diverse structure dominated by shorebirds and passerines, with the occurrence of waterfowl and raptors. Comparisons among habitats before construction showed that bird species richness, abundance, and diversity indices were higher in bare tidal flats than in S. alterniflora habitats, indicating that open tidal flats had higher value for the roosting and foraging of migratory waterbirds. Benthic fauna surveys showed that the number of benthic species increased after S. alterniflora removal and photovoltaic construction, and surface-dwelling food organisms such as crabs and mudskippers had relatively high biomass. The shading effect of photovoltaic panels may reduce the detectability and predation pressure of waterbirds on some surface-dwelling benthic organisms, and may also influence food resource structure by altering light conditions, temperature, and food supply in the sediment. Overall, with the combined implementation of S. alterniflora removal, tidal creek conservation, and halophyte restoration, tidal-flat photovoltaic areas may improve the original mono-dominant S. alterniflora habitat to some extent and provide foraging, roosting, and sheltering spaces for migratory waterbirds. This study provides a scientific basis for ecological planning of coastal tidal-flat photovoltaic projects and waterbird habitat conservation.