Q2. What are the future works mentioned in the paper "Interactions between polystyrene microplastics and marine phytoplankton lead to species-specific hetero-aggregation" ?
Since EPS/TEP production was not measured here, further studies are needed to confirm the hypothesis linking cell physiology, EPS and the formation of hetero-aggregates with micro-PS. Overall, the variety of MP occurring in the environment is more diverse ( polymer size, type, shape and concentration ) than the spherical MP commonly used in laboratory experiments and this should be adequately addressed in future studies ( Huvet et al., 2016 ). Future directions for field studies Observations of micro-PS adsorbing to suspended cells of C. neogracile and bacterial aggregates suggests that suspended particulate organic matter may influence MP buoyancy and settling in the water column ( and vice versa ), as already suggested for phytoplankton aggregates ( Long et al., 2015 ) and zooplankton faecal pellets ( Cole et al., 2016 ). Further studies moving towards more realistic scenarios ( e. g. natural plankton communities or mesocosm experiments ) are required to evaluate the ecological relevance of phytoplankton/MP hetero-aggregation.
Q3. How many micro-PS were suspended in the growth phase?
The fraction of micro-PS stuck to the glassware increased throughout the growth cycle up to 75 ± 4% at the end of the exponential growth phase (day 14), while 22 ± 4% of the remaining micro-PS were suspended and only 3 ± 1% were detected as hetero-aggregates.
Q4. What is the purpose of the present study?
The aim of the present study is to investigate the potential for marine phytoplankton cells to aggregate with micro-PS depending on phytoplankton species and physiological state under experimental conditions.
Q5. Why do conflicting results exist in the literature?
Due to confounding factors of MP dose and size in laboratory experiments, conflicting results on MP toxicity exist in the literature.
Q6. How did the present work highlight microplastics in seawater?
the present work highlighted the use of flow cytometry as a promising tool to quantify and characterize small microplastics (<200 µm) in seawater.
Q7. How many micro-PS were suspended in the stationary growth phase?
On day 3, no hetero-aggregates were observed and 79 ± 4% of the micro-PS appeared in suspension as free beads or homo-aggregates.
Q8. What was the definition of micro-PS partitioning in glass flasks?
Micro-PS partitioning in the glass flasks was defined as (i) free suspended beads, (ii) heteroaggregates constituted by micro-PS and microalgal cells and (iii) microbeads adsorbed to the glassware (on the flask walls).
Q9. What is the role of bacteria and algae in the formation of hetero-aggregations?
bacteria and algae can be associated to produce EPS, TEPs, and promote aggregation (Alldredge et al., 1993; Passow, 2002a,b).
Q10. What is the importance of adsorbing MPs in the environment?
MP distribution in different media (e.g. suspended, floating, adsorbed to experimental containers, trapped in organic aggregates, or adsorbed on or ingested by organisms) must be assessed to obtain accurate values of the actual MP concentration to which the organisms are exposed, as it is commonly done for other pollutant studies.
Q11. What is the ecological relevance of laboratory observations?
Although this study has highlighted a mechanism, the ecological relevance of such laboratory observations is likely low, as they are far from reflecting the complexity of the marine environment (relatively static conditions, small volumes, high algal cell concentrations, one microalgal species, one plastic type, size, dose, etc.).
Q12. What are the requirements for a better MP sampling at sea?
To make this possible, technological developments are required to improve MP sampling at sea, especially the fraction consisting of small MP, which may be associated with suspended organic and inorganic materials.
Q13. How many hetero-aggregates were observed in T. lutea?
in stationary growth phase (day 29), the proportion of hetero-aggregates consisting of diatoms and micro-PS reached 19 ± 6%.