Habitat transformation reshapes protistan community composition and assembly processes in coastal wetlands of southeastern China

Protists play essential roles in nutrient cycling, energy transfer, and microbial food web dynamics, yet their responses to anthropogenic habitat transformation in coastal wetlands remain underexplored. This study offers the first large-scale biogeographic assessment of sediment protistan communities across three contrasting coastal habitat types in southeastern China. We show that while alpha diversity remains resilient, profound shifts in community composition, functional group structure, and spatial turnover occur following <i>Spartina alterniflora</i> invasion and aquaculture conversion. Our findings underscore the primacy of environmental filtering, driven by salinity and sediment texture, in mediating these patterns and shaping community assembly. These insights not only expand our understanding of protistan ecology under coastal land-use change but also highlight their potential as sensitive bioindicators for monitoring ecological integrity and resilience in dynamic coastal systems.