Plastics are a new modification to the environment solely caused by humans. It is important to understand not only how plastics will possibly affect ecosystem functioning, but also how the ecosystem will influence the fate of plastics. In the ocean, buoyant microplastics are frequently found at the surface and within the water column, and biofilm formation may influence plastic’s buoyancy and distribute plastic to deeper layers. This study incubated high density polyethylene plastics in-situ in an estuary of the Chesapeake Bay & in-vitro, and examined biofilm formation through ATP, pigments, silica, and taxonomic composition of attached microbes using genomics and lipidomics. Even with six months of undisturbed nutrient-enriched in-vitro growth, biofilm accumulation did not induce negative buoyancy in a single plastic particle (6.2 x 0.48 mm²). Plastic sheets in situ incubated over a seven-week period accumulated a thick biofilm including abundant pennate diatoms that contain biogenic silica and thus contribute to ballast. However, a model based on the measured maximum accumulated silica and varying plastic thicknesses suggests that not even a plastic sheet as thin as a plastic bag, and bio-fouled on both sides, would become negatively buoyant; and the same plastic as thin as cling film would become negatively buoyant in freshwater only and not in seawater. Our results, overall, suggest that biofilms alone are unlikely to significantly influence the buoyancy of marine plastic debris.

Primary Presenter: Gregory Joern, Old Dominion University (gjoer001@odu.edu)

Authors:

Rut Pedrosa-Pàmies, The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA, USA  ()

Zhanfei Liu, Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA  ()

Xiangtao Jiang, Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA  ()

Alexander Bochdansky, Dept. of Ocean and Earth Sciences, Old Dominion University, Norfolk, VA, USA  ()