Abstract
Plastic pollution is widespread in ocean ecosystems worldwide, but it is unknown if plastic offers a unique habitat for bacteria compared to communities in the water column and attached to naturallyoccurring organic particles. The large set of samples taken during the Tara-Mediterranean expedition revealed for the rst time a clear niche partitioning be tween free-living (FL), orga nic particle-attached fi (PA) and the recently introduced plastic marine debris (PMD). Bacterial counts in PMD presented higher cell enrichment factors than generally observed for PA fraction, when compared to FL bacteria in the surrounding waters. Taxonomic diversity was also higher in the PMD communities, where higher evenness indicated a favorable environment for a very large number of species. were Cyanobacteria particularly overrepresented in PMD, together with essential functions for bio lm formation and fi maturation. The communit y distinction between the three habitats was consistent across the large-scale sampling in the Western Mediterranean basin. Plastic speci c bacteria recovered only on the PMD ' fi ' represented half of the OTUs, thus forming a distinct habitat that should be further considered for understanding microbial biodiversity in changing marine ecosystems.