Effects of the Interaction Between Algae and Microplastics on Life-History Traits of Daphnia Pulex Clones

Abstract

Microplastic (MP) pollution is potentially a big threat to many aquatic organisms. However, we currently know very little about the effects of small MPs on phenotypes and the extent to which genetic and environmental factors modify the effects of MPs. I studied the direct and indirect effects of 9.5 - 11.5 μm polystyrene microspheres on the life history traits (time to maturation, total number of offspring, size of adults) of Daphnia pulex clone Bel 19 and Bel 87. The D. pulex clones were exposed to two different concentrations (low 0.001 mg/l and high 1 mg/l) of MP. Each clone had two groups of individuals. One group of individuals was fed with algae food (no MP aging) to observe direct effects, and another group with algae food (MP aging) to observe indirect effects on the life history traits. MPs were aged in algae suspension for 7 days. Individuals were fed with an amount of carbon concentration 1 mg/l. I used laboratory exposure to answer the research questions - 1) do D. pulex clones differ in the susceptibility to MP pollution in terms of life history traits? and 2) are there any signicant differences between direct and indirect effects of MPs on life history traits of D. pulex clones? The results from the study showed that the D. pulex clones differ signicantly in the susceptibility to MP pollution in terms of the observed life history traits, which demonstrate the importance of incorporating genetic variation into the assessments of the impacts of plastic particle exposure. Signicant differences were also observed between the direct and indirect effects of MP on life history traits of D. pulex clones. Among the observed traits, time to maturation is the most affected one by indirect effect with the largest effect size (almost 3 times higher than the direct effect size). The results indicate that indirect ecological effects might lead to effect thresholds at levels considered eld relevant to the direct effects