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Microbial carrying capacity and carbon biomass of plastic marine debris


Trillions of plastic debris fragments are floating at sea, presenting a substantial surface area for microbial colonization. Numerous cultivation-independent surveys have characterized plastic-associated microbial biofilms, however, quantitative studies addressing microbial carbon biomass are lacking. Our confocal laser scanning microscopy data show that early biofilm development on polyethylene, polypropylene, polystyrene, and glass substrates displayed variable cell size, abundance, and carbon biomass, whereas these parameters stabilized in mature biofilms. Unexpectedly, plastic substrates presented lower volume proportions of photosynthetic cells after 8 weeks, compared to glass. Early biofilms displayed the highest proportions of diatoms, which could influence the vertical transport of plastic debris. In total, conservative estimates suggest 2.1 × 1021 to 3.4 × 1021 cells, corresponding to about 1% of the microbial cells in the ocean surface microlayer (1.5 × 103 to 1.1 × 104 tons of carbon biomass), inhabit plastic debris globally. As an unnatural addition to sea surface waters, the large quantity of cells and biomass carried by plastic debris has the potential to impact biodiversity, autochthonous ecological functions, and biogeochemical cycles within the ocean.

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Fig. 1: Three-dimensional visualization of biofilm on four substrates after 1 week (left column) and 8 weeks (right column) of immersion.
Fig. 2: Cell abundance (105 × cells/mm2) on four substrates after 1 week and 8 weeks of immersion.
Fig. 3: Curves show kernel density estimations for the cell length distributions on four substrates after 1 and 8 weeks of immersion.
Fig. 4: Temporal development of biofilms over the incubation period on four substrates (polyethylene (PE), polypropylene (PP), polystyrene (PS), glass (Glass)).

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All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.


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Thanks to Gregory Boyd, Jessica Fields, and Kiera Saleem for their help with sampling. We also thank Louis Kerr of the Central Microscope Facility at the Marine Biological Laboratory for technical support. The work was also supported by NSF collaborative grants to LAA-Z (OCE-1155571), ERZ (OCE-1155379), and TJM (OCE-1155671), NOAA grant NA17NOS9990024 to LAA-Z an American Chemistry Council award to LAA-Z, ERZ, and TJM, and funds from FAU World Class Faculty and Scholar Program to TJM.

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All authors were involved in conceiving the study. TJM, SZ, LAA-Z, and ERZ designed the experiments; TJM, LAA-Z, and ERZ conducted the incubation experiment. SZ analyzed the samples. SZ carried out the data analysis and wrote the paper with significant assistance and comments from all the other authors.

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Correspondence to Tracy J. Mincer.

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Zhao, S., Zettler, E.R., Amaral-Zettler, L.A. et al. Microbial carrying capacity and carbon biomass of plastic marine debris. ISME J 15, 67–77 (2021).

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