Spatial redistribution difference between particle associate and free living bacteria in a micro-tidal influenced estuary

Abstract

Microbial community variation in estuaries had been a research hotspot in recent years, but the effects of hydrodynamic forces on bacterial community redistribution remain underexplored. This study presents fixed-point observations of bacterial community redistribution under hydrodynamic influence during both dry and wet seasons. Alpha diversity analysis indicated that the bacterial community in the dry season exhibited higher richness and diversity than in the wet season, likely due to weaker hydrodynamics and lower temperatures. Co-occurrence network analysis showed that particle-associated (PA) communities had lower network diameter, graph density, and average path length than free-living (FL) communities. The FL community was more affected by vertical mixing, while the PA community was more affected by bottom flow. It is speculated that variation in the FL community results from the mixing of seawater and river water bacteria, which are more affected by surface currents, whereas PA community variation is driven by sedimentation and the bottom flow transport of particles. Unlike FL taxa, which correlated with real-time flow, PA taxa showed a stronger correlation with the flow data 1 h in the past, likely due to the greater inertial resistance of particulate matter compared to bacteria. This study highlights the differential behavior of PA and FL communities under hydrodynamic forces, enhancing the understanding of factors influencing bacterial community variation in estuaries.