In order to understand the impacts on plastics as a substrate in the marine environment, microorganisms that are preferentially colonize and interact with plastic surfaces, as opposed to generalists potentially colonising everything, need to be identified. Accordingly, it was hypothesized that i.) plastic “specific” microorganisms are closely attached to the polymeric surface and ii.) that specificity of plastics biofilms are rather related to members of the rare biosphere. To answer these questions, a three phased experiment to stepwise uncover closely attached microbes was conducted. In Phase 1, nine chemically distinct plastic films and glass were incubated in situ for 21 months in a seawater flow through system. In Phase 2, a high-pressure water jet treatment technique was used to remove the upper biofilm layers to further, in Phase 3, enrich a plastic “specific” community. To proof whether microbes colonizing different plastics are distinct from each other and from other inert hard substrates, 16S rRNA gene tag sequencing was performed. Our findings indicate that tightly attached microorganisms might account to the rare biosphere and suggest the presence of plastic “specific” microorganisms/assemblages which could possibly benefit from the given plastic properties or at least grow under limited carbon resources.