Abstract
Microplastics (MPs) are commonly defined as microscopic plastic particles sized between 100 nm and 5 mm; a size range covering many plankton species including microalgae. Interactions between MP particles, algal cells and their planktonic predators can therefore not be excluded. Microalgae are keystone organisms in marine ecosystems on which the whole food chain depends. Consequently, impact assessment of MP pollution on the marine environment warrants the study of effects on lower trophic levels of marine ecosystems. Populations of selected microalgae species including the cryptophyte Rhodomonas baltica and the dinoflagellate Oxyrrhis marina are therefore exposed to environmentally relevant concentrations of comprehensively characterized 10 m particles of low density polyethylene (LDPE) and general purpose polystyrene (GPPS). Custom-made transparent plankton wheels immersed in a water bath are used to expose these phytoplankton species in a (semi-)static setup in order to keep MP and algal cells in suspension, and maintain constant temperature and light conditions. Exposure effects on biomarkers of fitness with ecological consequence are studied using R. baltica. For example effects on growth/production are evaluated by measuring changes in growth rate and population size (cell number), biomass (cell size), maximum carrying capacity (maximum number of algal cells in the population), pH change in the exposure media, and chlorophyll production. In addition, MP uptake by O. marina is investigated and its effect on O. marina sinking speed measured.