Impact of polystyrene microplastics on major marine primary (phytoplankton) and secondary producers (copepod)

The effect of microplastic adsorption on marine microalgae Tetraselmis suecica, Amphora subtropica, and copepod Pseudodiaptomus annandalei was investigated in the present study. Fluorescence microscopic images were used to evaluate MP interactions with algae and copepods. T. suecica growth rate decreased with effects of 0.1 µm polystyrene exposure to 75 µl/100 ml (0.899 to 0.601 abs), 50 µl/100 ml (0.996 to 0.632 abs) and 25 µl/100 ml (0.996 to 0.632 abs), respectively. On the other hand, at 10th day of experiment, the control T. suecica showed the highest growth rate (0.965 abs), chlorophyll concentration (Chl-'a' = 21.36 µg/L; Chl-'b' = 13.65 µg/L), and cell density (3.3 × 10 cells/ml). A marine diatom A. subtropica absorbed 2.0 μm microplastics, and the maximal inhibition rate increased at higher MP concentration until 10th day. The highest MPs (75 μl/100 ml) treatment resulted in decreased growth rate of A. subtropica from 0.163 to 0.096 abs. A. subtropica (without MPs) had the highest lipid concentration of 27.15%, whereas T. suecica had the lowest lipid concentration of 11.2% (without MP). The maximum survival (80%) of P. annandalei was found in control on 15th day whereas on 12th day, the microplastics ingested copepod had the lowest survival rate (0%). On 15th day, the maximum Nauplii Production Rate (NPR) (19.33) female was observed in control, whereas the minimum (17.33) female NPR was observed in copepod ingested with MPs. The maximum lipid production (17.33% without MPs) was reported in control, whereas MPs fed copepods had the lowest lipid production (16%). Long-term exposure to polystyrene microplastics significantly reduced algae growth and chlorophyll concentration and also NPR and lipid concentration rate of copepod. We inferred that microplastic exposure of algae and copepods might results in persistent decreases in ingested carbon biomass over time.