Differential responses of phytoplankton and zooplankton communities to tidal and urban stressors in the Dongjiang river: From biodiversity patterns to network stability

This study employed environmental DNA (eDNA) metabarcoding to investigate the differential responses of phytoplankton and zooplankton communities to combined tidal and urban stressors along the Dongjiang River, China. The results revealed distinct spatiotemporal patterns between phytoplankton and zooplankton groups: phytoplankton diversity showed significantly stronger seasonal variation (a 61.2 % increase in the wet season, P < 0.05), particularly in tidal urbanized reaches, whereas zooplankton exhibited greater stability (with only 12.8 % seasonal variation). Community assembly analyses demonstrated contrasting mechanisms-phytoplankton shifted from stochastic dominance (53.4 % explained by neutral models) in wet seasons to deterministic control (6.8 %) in dry seasons, while zooplankton remained consistently deterministic (<1 % neutral model fit) across all conditions. Network analysis revealed significant fragmentation of phytoplankton interactions in tidal urban zones, whereas zooplankton networks maintained higher stability despite reduced complexity. Temperature, nitrogen nutrients, and organic pollutants were identified as the key environmental drivers affecting phytoplankton and zooplankton community composition in the Dongjiang River. This study demonstrates how eDNA-based approaches can disentangle complex stressor interactions in urbanized estuaries, highlighting the role of seasonal hydrological variations, and provides a scientific basis for ecological management strategies aimed at preserving aquatic biodiversity and river ecosystem health.