Bioavailability of microplastics to marine zooplankton and implications for ecosystem services

Microplastics are a pervasive pollutant of environmental concern. Their small size means they are bioavailable to a wide range of species, including zooplankton, an important group of organisms at the base of the marine food web, which also play a crucial role in carbon and nutrient cycling. Previous research has shown that microplastics are readily ingested by zooplankton and at high concentrations can affect feeding behaviour, growth/development, and reproduction. However, to develop effective risk assessments for zooplankton species, populations, and the wider ecosystem, we need to better understand the underlying mechanisms and factors that influence microplastic uptake, microplastic uptake by zooplankton in the natural environment, and the impact of ingestion on the wider ecosystem and human well-being. In this thesis I help address these, by using a suite of feeding experiments, laboratory analysis of field samples, and by conducting an impact analysis of the ecosystem services. My research reveals that: 1) the factors of shape and presence of infochemicals can affect the bioavailability of microplastics to zooplankton, highlighting that the selectivity of some species and those that use chemosensory mechanisms, may be at an increased risk of microplastic ingestion; 2) microplastics were present in all species of Arctic zooplankton investigated, all were fragments and the majority were below 50 µm, amphipods ingested significantly more than copepods which may be due to life history traits; and 3) zooplankton provide important ecosystem services including climate regulation, other materials, and entertainment. High microplastic concentrations and climate change are evidenced to have the most substantial negative impacts on copepods and krill, with accompanying implications for their ecosystem services. Overall, my research contributes to our understanding of why microplastics are ingested by zooplankton, furthers the knowledge base of microplastic ingestion in the field, and provides evidence of impacts to the wider ecosystem and human well-being.