Biofilm Development on Macroplastics along a Freshwater-Estuarine Gradient with Attention to Diatom Assemblages

Plastic pollution poses a significant and persistent threat to the health and functioning of aquatic ecosystems worldwide. The development of microbial communities on freshwater macroplastics can affect nutrient cycling and facilitate biotic dispersal, while characterisation of biofilm assemblages can inform on residency time, pathways and accumulation patterns of aquatic plastics. Polypropylene, polyethylene terephthalate, and polystyrene coupons were incubated in the River Great Ouse, UK for 21 days at locations with increasing salinity. Biofilm abundance was quantified using crystal violet staining and spectrophotometry and community composition was characterized through Scanning Electron Microscopy (SEM) image analysis. Here, we show how time, plastic type, and site impact biofilm development and composition, with special attention to diatoms, on aquatic plastics. Site was the most determinant factor for biofilm abundance. However, we found no plastic specific nor site specific assemblages of biofilm diatom communities. This study highlights the stochastic nature of biofilm development on plastics in freshwater-estuarine systems as well as the factors that must be considered in dynamic aquatic environments, like hydrological conditions of the site, that challenge simple community development models that have been used for marine environments.