Contrasting Lifestyle of Free-Living and Particle-Attached Microbes Shaped Community Dynamics and Stability in the...

Seamounts are unique marine environments that are recognised as biodiversity hotspots in oligotrophic oceans. They contain highly productive ecosystems that are supported by diverse microbial communities, but they are susceptible to anthropogenic disturbances such as fishing. However, knowledge of the biogeographic distribution, assembly mechanisms and co-occurrence patterns of microbial communities with different lifestyles above seamounts remains largely unexplored. We sampled above the seamount in the South China Sea to compare the varied dynamics of free-living and particle-attached microbial communities. Overall, the microbial community in the seamount region exhibited the same richness compared to those in the DCM (Deep Chlorophyll Maximum) layer, while the network demonstrated higher complexity and robustness. The distance-decay analysis results indicate that particle-attached microorganisms significantly declined with increasing geographical distance, demonstrating that they are more sensitive to geographical distance and have strong habitat endemicity. Microbial community assembly was governed more by stochastic processes, with the assembly of free-living and particle-attached microbes dominated by homogeneous selection and dispersal limitation, respectively. The influence of stochastic processes was strengthened with increased richness of free-living microbes, whereas particle-attached microbes were not. Particle-attached prokaryotic communities showed complex associations, lower robustness, and higher vulnerability compared to the surrounding free-living communities. Overall, these results broaden our knowledge of free-living and particle-attached prokaryotic communities in seamount ecosystems and provide critical insights into the microbial community assembly and network stability in the seamount region, implying their potential differential responses to future environmental disturbances.