Salinity-topography synergy drives macrobenthos community assembly in mangrove-stream ecotones: Management implications for coastal restoration

In estuarine and coastal ecosystems, the freshwater-saltwater interface serves as a core zone for land-sea interactions. The mangrove-stream ecotones within this interface exhibit highly dynamic microenvironmental differentiation through synergistic salinity-topography gradients. However, the multidimensional biodiversity drivers regulating macrobenthos community assembly within these dynamic transition zones remain critically underexplored. This study investigated macrobenthos community assembly across mangrove wetlands and five estuarine streams in Fuding, China. By integrating diversity indices with multivariate modeling, we compared spatial differentiation patterns and environmental drivers. Results indicated that mangroves supported significantly higher α-diversity, functional richness, and redundancy than streams, which exhibited higher functional vulnerability. While taxonomic β-diversity in both ecosystems was predominantly driven by species turnover, mangroves exhibited significantly higher functional β-diversity than streams, which were characterized by low functional turnover and high structural instability. Dissolved oxygen, salinity and elevation were identified as key environmental factors driving the structure of mangrove communities. In contrast, stream communities primarily responded to salinity, elevation and pH gradients. These differences confirmed the interplay between salinity and topographic factors. Consequently, we established a differentiated management framework. Mangrove conservation requires the maintenance of heterogeneous habitats with a tidal-elevation gradient in order to enhance functional redundancy. Stream conservation should involve the regulation of salinity fluctuations and the increase of functional turnover rates. This ultimately strengthens the resilience of the interaction zone. This study establishes the first regional-scale macrobenthic indicator system for mangrove-stream ecotones, providing a scientific basis for adaptive coastal management under global change. • First regional-scale study investigating macrobenthic biodiversity drivers in mangrove-stream ecotones was conducted. • Mangroves supported higher taxonomic and functional diversity but lower functional vulnerability than streams. • Mangroves exhibited significantly higher functional β-diversity than streams. • Community assembly was differentially driven by salinity-topography gradients in the two ecosystems. • A management indicator framework was established for adaptive conservation of coastal resilience.