Investigating Microplastic Ingestion by Zooplankton

Microplastic pollution is a ubiquitous threat in the marine environment. The ingestion of microscopic debris (<5 mm) by marine zooplankton is a phenomenon of high ecological concern. This thesis presents new information regarding the ingestion of microplastics by marine zooplankton. The calanoid copepod, Centropages typicus, abundant in North Atlantic and Mediterranean coastal waters was found to ingest Polyamide-6 Nylon powder (μ = 30 μm), Polyethylene microbeads (μ = 20 μm) and artificial rope fibres (μ = 14.76 μm) that had been labelled with RADGLO fluorescent powder (475 nm) in the presence and absence of natural prey. Feeding experiments were conducted upon four zooplankton species; Acartia tonsa, Porcellanid larvae, Calanus helgolandicus and Oithona similis. Exposure to microplastic particles resulted in an energy deficit in all species with the exception of O. similis when feeding upon a natural assemblage of algae for 24 hours, though this was only statistically significant for A. tonsa exposed to a mixture of 10 μm and 20 μm Polystyrene spheres (100 particles mL-1). Zooplankton displayed altered feeding behaviour. High-speed video analysis allowed for the mechanisms of microplastic detection, capture and subsequent rejection or ingestion to be observed. It was found that long-range chemodetection is unlikely to occur; rather cells are detected upon contact with setae. Individuals appear to reject microplastic particles in response to the physical properties of microplastic particles. These studies provide fundamental information on the ingestion and biological effects of microplastic debris upon zooplankton, knowledge of which is important given the key role that zooplankton play in the transfer of energy to higher trophic levels and, thus, ecosystem function. These findings provide pathways for further research and highlight the influence that feeding strategy and prey selectivity may have in determining the negative effects associated with microplastic uptake.