LAUSR

Marine microbes play important roles in the development of phytoplankton blooms. The diversity and composition of free living (FL) and particle attached (PA) microbial communities have been well studied, while little is known about their geographic and co-occurrence patterns, especially during the subsiding process of Phaeocystis globosa blooms. Herein, the beta-diversity of FL and PA microbial communities in both the surface and bottom layers of different habitats were comprehensively examined during succession of a P. globosa bloom event. The results showed that microbial communities from bloom and non-bloom sites exhibited distinct community compositions. Among the different sampling sites, the community similarities decreased with spatial distance, in which the FL communities' similarity in bottom waters was more influenced by spatial variation. The variation of microbial communities was mostly attributed to environmental selection, spatial distance, and the abundance of P. globosa successively. The co-occurrence networks of microbial communities in bloom and non-bloom waters differed in terms of structure and composition, and the bloom network had more links and closer relationships between genera than the non-bloom network. The correlation among genera and modules suggested that the bloom microbes were likely driven by high environmental selection and low competitive effect between each other.