Spatial and seasonal variations in biofilm formation on microplastics in coastal waters

At present, microplastics (MPs) have gradually become a hot issue in marine environmental pollution and may pose a potential threat to marine ecosystems. Since MPs are not easily biodegradable, they can provide the attachment substrates for various organisms, which will affect their floating and transport, and may also lead to the invasion of harmful microorganisms. In this study, polypropylene, polyethylene, polylactic acid pellets, and glass particles were exposed for 6 weeks in different seasons at three stations in the Yellow Sea, China. The results showed that the total amounts of biofilms significantly varied among seasons and functional zones and that the temperature of seawater was the main influencing factor. A variety of biological communities (especially diatoms and bacteria) and extracellular polymeric substances were observed on the MP surfaces using scanning electron microscopy and confocal laser scanning microscopy. Sequencing analysis indicated that the structure and composition of microbial communities on MPs mainly varied with seasons and locations. In addition, most of the microorganisms were generally attached to the surface and were not any specific selection of plastic by different chemical compositions. However, the bacteria inhabiting microplastics harbored distinct metabolisms. Our results suggest that low-density MPs may settle quickly in summer in some eutrophic areas.