Synchronous responses to tidal restriction by seawall construction across fish and plankton communities in Yangtze River Estuary

Tidal restriction caused by seawall construction exerts profound impacts on coastal wetland ecosystems, typically aimed at restoring vegetation and avian diversity. However, studies on non-target aquatic organisms under tidal restriction remain scarce. In our study, we hypothesized congruent responses of fish, zooplankton, and phytoplankton communities to tidal restriction between naturally unrestricted creeks and tide-restricted marshlands in Chongming Dongtan, Yangtze River Estuary. Shifts in community structure were observed across all three taxonomic groups but lacked statistical significance, likely due to the early stage of seawall construction and semi-regulated operation of sluices in the Dongtan wetland. Notably, biodiversity disparities emerged primarily in higher trophic levels, with declining trends in fish and zooplankton diversity in tide-restricted areas, whereas phytoplankton communities exhibited comparable diversity between habitats. Structural equation modeling (SEM) revealed a significant negative effect of salinity on fish communities, with no detectable top-down or bottom-up cascading effects in aquatic food chains, further indicating that abiotic factors outweigh biological interactions in governing ecosystem dynamics.