Habitat heterogeneity shapes aquatic community diversity in the Liaohe Estuary wetland, China

Estuarine wetlands develop pronounced habitat heterogeneity along land-sea gradients, yet the differentiated responses of aquatic communities among vegetation habitats and their environmental drivers remain poorly understood. Focusing on four typical habitats in the Liaohe Estuary wetland — Phragmites australis wetland (PA), Suaeda salsa-Phragmites australis wetland (SP), Suaeda salsa wetland (SS), and mudflat wetland (MF) — this study systematically analyzed the community structure, biodiversity, density, and biomass of phytoplankton, zooplankton, benthic macroinvertebrates, and fish, as well as their responses to environmental factors. The results showed that aquatic communities in the Liaohe Estuary exhibited ordered succession and habitat specificity along the land-sea gradient. Salinity was the key driver shaping aquatic community patterns, its effects differed among different aquatic communities, suppressing phytoplankton diversity while promoting fish diversity. Dissolved oxygen showed a stronger bidirectional regulatory effect, being significantly positively correlated with fish community characteristics but significantly negatively correlated with phytoplankton community characteristics. Different vegetation types displayed marked functional differentiation and habitat complementary, SP sustained phytoplankton and benthic macroinvertebrate diversity, SS supported a highly even fish community, MF served as a key habitat for zooplankton and consumer communities, and PA maintained high primary-producer diversity, jointly sustaining the overall biodiversity of the Liaohe Estuary wetland. These findings indicate that the structural and functional stability of the Liaohe Estuary wetland ecosystem depends on the integrity of the land-sea continuum, as well as on environmental gradients.