The plastisphere: a comprehensive description of geographic and temporal community patterns across the Mediterranean Sea and the Atlantic Ocean.

Plastic pollution is a global ecological threat, not only as physical debris but also as a novel substrate hosting microbial communities, known as "plastisphere". Polymer type (virgin vs. recycled), combined with environmental variations, may influence both early and mature colonization stages. While biogeography has been identified as a key driver of the plastisphere community structure, prior research often relied on isolated studies with no methodological standardization or on opportunistic sampling. Here, this study stands out by conducting a simultaneous and harmonized investigation across environmentally distinct sites in the Mediterranean Sea and the Atlantic Ocean. Three polymers (LDPE, PP-PC, PLA) were incubated in situ, across six locations. Using standardized protocols and eDNA metabarcoding (16S and 18S rRNA), we assessed how biogeography, environmental variables, polymer type, and exposure time shape the diversity and composition of prokaryotic and eukaryotic communities colonizing plastics. Incubations lasted up to one year, with sampling at 7, 30 and 90 days, covering all four seasons. Microbial colonization in all plastics occurred within 7 days, but community richness and maturity fluctuated across sites and seasons. Proteobacteria, Bacteroidia and Planctomycetes were the dominant prokaryotes, while Ciliophora, Cercozoa and Dinoflagellata dominated eukaryotes. Taxa with potential for plastic biodegradation (e.g., Oleibacter, Alcanivorax) and pathogenicity (e.g., Pseudomonas, Candida) were identified, highlighting the plastisphere's ecological role. This dataset represents the most comprehensive assessment of marine plastisphere diversity to date, allowing the understanding of species occurrence and their interactions, influence on ecological processes and the emerging health risks of the plastisphere, which should be considered when developing global strategies to mitigate ocean plastic pollution.