Plastic Type and Condition Have Minimal Impact on Associated Marine Biofilm Communities

The ecological impacts of plastics and their additives on marine microbiota remain unclear. We applied prokaryotic 16S rRNA gene and fungal ITS2 region amplicon sequencing, alongside shotgun metagenomic sequencing, to identify compositional and functional changes in microbial communities on marine plastic. Five common plastics, both non-aged and artificially aged, were submerged in Auckland Harbour, Aotearoa-New Zealand. Biofilms on linear low-density polyethylene (LLDPE), nylon-6 (PA), polyethylene terephthalate (PET), polylactic acid (PLA), oxo-biodegradable LLDPE (OXO) and glass were sampled over 12 months. The taxonomy and functional potential of biofilm communities differed from surrounding seawater communities and varied with biofilm age. Younger biofilms were more diverse, with Proteobacteria, unknown fungi and unclassified Metazoa dominating prokaryotic, fungal and eukaryotic communities, respectively. Taxa related to previously reported plastic-degraders were found in very low abundance across all substrates. Plastic type and UV-ageing did not significantly shape biofilm communities over a year. Although some genes differed in relative abundance due to UV-ageing, overall functional profiles remained consistent across plastics. Genes conferring reported plastic-degrading traits were present regardless of plastic type, UV-ageing and biofilm age. Nevertheless, nylon hydrolases were notably associated with PA, suggesting marine plastic impacts may be restricted to taxa or functions involved in its degradation.