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

Abstract

Coastal wetlands along southeastern China have undergone extensive habitat transformations, notably from natural mudflats (MFs) to Spartina alterniflora marshes (SAs) and aquaculture ponds (APs), yet the ecological consequences for sediment protistan communities remain largely unknown. Here, we systematically examined protistan diversity, community composition, functional groups, and assembly processes across 21 wetlands spanning five provinces using amplicon sequencing. Although alpha diversity remained stable across habitat types, community composition and functional group distributions were significantly altered. In particular, phototrophic protists declined markedly following S. alterniflora invasion and then increased after aquaculture pond reclamation. Meanwhile, consumer and phototroph assemblages were strongly influenced by sediment grain size. Salinity emerged as the key environmental driver of protistan diversity and community structure. Distance-decay relationships indicated elevated spatial turnover in SAs, suggesting increased environmental filtering after plant invasion. Assembly process analysis revealed a dominance of deterministic mechanisms in shaping community structure across all habitats, with the strongest signal observed in SAs. These findings demonstrate that land-use change reshapes protistan communities through altered environmental constraints, highlighting the ecological sensitivity of microbial eukaryotes to anthropogenic disturbance in coastal wetland ecosystems.