Persistent microplastic pollution in the marine environment is inseparable from the plastisphere, the microorganisms that form biofilms on their surface. This plastisphere has major implications for the potential impact of microplastics on marine ecosystems and their fate. Indeed, it would concentrate bacteria different from the surrounding sea water, potentially pathogenic such as Vibrio sp. or on the contrary, capable of directly degrading the plastic polymer. Despite this major issue, we have little information about the development and evolution of this biofilm throughout the life of a microplastic. The question of the specificity of the biofilm compared to natural substrates of seawater is also debated.Moreover, this plastisphere appears to change with time and space and few studies have addressed both aspects at the same time. Here, in an experiment taking into account the two factors of time and space, 8400 plastic particles were deployed in oyster bags in a shellfish farming area in Brest harbor. The bacterial communities associated with the plastic particles were studied in 4 different areas on the foreshore (intertidal or subtidal environment, close or not to the sediments), on three types of polymers (PVC, PE and PP) and in incubation times ranging from 7 days to 147 days. The diversity of the bacterial community associated with these plastic particles was studied by metabarcoding approach. In agreement with what is already described in the literature, our study confirms that the composition of the bacterial biofilm on the surface of microplastics is different from that of free-living bacteria or those colonizing particles naturally present in seawater. However, these differences are shown to be less important between microplastics and large seawater particles, mainly zooplankton. This bacterial biofilm on microplastics appears to be highly variable, depending on the environment, the type of polymer and the incubation time. Microplastics incubated in intertidal environments show biofilms dominated by filamentous cyanobacteria, which are known to be well adapted to strong variations in temperature or salinity, linked to the alternating tides. An interesting result of this work is that these cyanobacteria are however significantly less abundant on PVC compared to PE and PP. This could reflect an inhibition of their growth by the additives present on PVC. Our study shows that environmental pressures are present as early as 7 days of immersion of the microplastics and up to 140 days of incubation in seawater, suggesting that the bacterial biofilm will be permanently subjected to the environment. However, despite this important heterogeneity, we observe that the composition of the plastisphere presents a precise succession in time, with bacterial taxa such as Pseudoalteromonas, involved in the establishment of the biofilm that are present in abundance only in the first weeks of incubation (7-14 days of incubation) and will be in the minority afterwards. A comparison of the presence and abundance of these bacteria on bacterial biofilms of floating microplastics collected in Brest roadstead in a previous study (Frère et al. 2018) shows that these biofilm-initiating bacteria could represent up to 50% of the bacterial communities associated with these floating microplastics. This result suggests that these plastic particles had been submerged in the roadstead for a relatively short time, which corresponds well with the estimated residence time of microplastics in the Brest roadstead of approximately 10 days. However, these taxa belong to classical bacterial genera (i.e. Alteromonas, Pseudoalteromonas) of the plastisphere, found in different seas and ocean basins with probably much longer residence times for microplastics. An interesting hypothesis would be that the biofilm on a plastic particle would not persist in its initial state (or composition) and on the contrary would undergo repeated colonizations during its life on the ocean surface. These results underline the importance of taking into account the time and space aspects in the impact studies of microplastic contamination in the environment and raise interesting hypotheses to better understand and manage their impact on marine ecosystems.