Microplastics have emerged as a new anthropogenic substrate that can readily be colonized by microorganisms. Nevertheless, information of the assembly processes and long-term variations of microplastic-type specific microbial communities in coastal maricultural waters remains limited. Using an in situ incubation experiment, 16S rRNA gene amplicon sequencing and ecological analysis, we investigated the prokaryotic communities attached to polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP), as well as water fractions in a mariculture cage in Xiangshan Harbor, China. All microplastic-associated prokaryotic communities were significantly distinct from free-living (FL) and small particle-attached (SPA) communities in waters, but relatively similar to large particle-attached (LPA) communities. Although each of the three microplastics developed distinct prokaryotic community, PE and PP were found to more closely resemble each other. Furthermore, the prokaryotic community dissimilarity among all substrates tended to decrease over time. In addition, the hydrocarbon-degrading bacteria Alcanivorax showed selective colonization on PE, and PET might be carriers of?pathogenic Vibrio, increasing the ecological risk of PET in maricultural environments. Neutral model predictions suggested that neutral process dominated the prokaryotic assembly of PE and PP, while selection was more responsible for the composition of PET plastisphere. Planctomycetaceae and Thaumarchaeota Marine Group I were identified as important members that contribute specifically to selection and neutral processes, respectively. Our study provides further understanding of microplastic-associated microbial ecology in maricultural environments.