| Summary: | Plastic debris are ubiquitous, and the Arctic is no exception. Despite the relatively low population number around the Arctic, abundances of microplastic litter are like those of the most polluted subtropical areas. Micro- and nanoplastics have been found in Arctic fauna, but due to constraints in methodology, measurements of nanoplastics in sea water have not been carried out yet. Micro- and nanoplastic toxicity tests have recently executed in phytoplankton single species but no literature exists of Arctic taxa, and there is little knowledge how complex communities respond to nanoplastic exposure. To bridge these knowledge gaps, this thesis carried out two experiments, where 1) two sub-Arctic diatoms (Chaetoceros gelidus and Thalassiosira gravida) were chronically exposed to polystyrene nanoplastics over the course of their exponential and stationary phases, testing for growth and biochemical responses and 2) Arctic phytoplankton communities from the Barents Sea Polar Front were incubated with polystyrene nanoplastics for 3 h. It was assumed that, because some species, such as C. gelidus produce high concentrations of sticky transparent exopolymer particles (TEP), that they would have the highest levels of adherence in both experiments. The single species study did not yield any results. Phytoplankton community experiment proved species-specific adherence of nanoplastics, however, contradictory to our hypotheses, presence of TEP may not be the determining factor in adherence. We suggest that, because of the species-specific adherence, there may be a seasonal cycle in adherence related to the seasonality of phytoplankton taxa. These results prove that in the future, natural community experiments must be carried out at an increasing level.
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