Incorporation of microplastic particles (MP) into the microbial food web and their further transfer to higher trophic levels has been hitherto poorly studied. The patterns of MP uptake by the unicellular heterotrophic dinoflagellate Oxyrrhis marina (OXY) were studied. The prymnesiophycean Isochrysis galbana (ISO), 5.6-µm polystyrene microspheres (MS) and a mixture of both (ISO-MS) were used as prey for O. marina. Dynamics of microorganisms and microspheres concentrations in the experimental vessels were studied using a flow cytometer. Dinoflagellates ingested MP even in the presence of their natural prey (microalgae), and feeding on MP did not result in a decrease in O. marina abundance. Grazing rates in the mixture experiment (OХY-ISO-MS) were 0.21 ± 0.01 MS/cell/h (±SD) and 0.38 ± 0.01 ISO/cell/h, respectively. Rates were significantly lower than in the mono-diet experiments (1.93 ± 0.68 ISO/cell/h and 0.45 ± 0.04 MS/cell/h, respectively). Thus, expanding the range of food objects led to a decrease in the rate of their ingestion. In the experiments with a mono-diet the clearance rates were 0.12 ± 0.04 μl/cell/h (OХY-ISO) and 0.19 ± 0.06 μl/cell/h (OXY-MS), respectively, i.e. dinoflagellates spent less time on capturing microalgae compared to MS. The same pattern was observed in the experiments with the prey mixture (OХY-ISO-MS): the clearance rate of microalgae (0.17 ± 0.02 μl/cell/h) was slightly lower than that of microspheres (0.19 ± 0.003 μl/cell/h). Since O. marina re-consumed MS even in the presence of natural food objects, no trophic adaptation of dinoflagellates to MS occurred. Selective grazing of dinoflagellates was not revealed for any prey, either for ISO, or for MS. These results indicate the possibility (and high probability) of the inclusion of MP in the microbial food web and the important role of unicellular organisms in the transfer of MP to higher trophic levels.


T. V. Rauen
V. S. Mukhanov



L. O. Aganesova





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