Plastic habitats: Algal biofilms on photic and aphotic plastics

Plastic pollution is abundant in aquatic environments worldwide and many of its detrimental impacts are well documented, but it also represents a novel substrate available to a diversity of organisms. Biofilms – assemblages of bacteria, algae, and fungi – colonise hard surfaces in aquatic environments. They are key agents in biogeochemical cycling and are a food source for grazing organisms, representing a keystone aquatic community, and are known to influence the fate of plastic pollution in aquatic environments. In one of the most temporally thorough assessments of biofilm development on freshwater plastics, here we report on the evolution of algal biofilm assemblages on three plastic polymers (Low Density Polyethylene, Polypropylene, and Polyethylene Terephthalate) over six weeks in the photic and aphotic zones of a freshwater reservoir in Staffordshire, UK. Significant differences were found between diatom assemblages on plastics in the photic and aphotic zones, and between diatom assemblages quantified on weeks 2, 4 and 6 of the study, but total algal photosynthetic pigment concentrations did not vary significantly between polymers in either zone. Scanning Electron Microscopy indicates that degradation of polymer surfaces occurs within six weeks in the aphotic zone, with potential implications for plastic fragmentation and microplastic generation.