Houvener, Jacob (2022) Effects of macroplastic litter on Mytilus galloprovincialis communities in northwestern Spain. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 60 pp.

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Abstract

Plastic litter in the ocean has gained significant attention over recent decades, with the current focus shifting to micropiastics. Macroplastic litter, on the other hand, has spread throughout all parts of the oceans, coming into contact with hundreds of species. The effects on single organisms is well documented, but few studies have researched the impacts of macroplastic litter on the community level. In this study I investigate the effects of a low and high amount of fishing line and shopping bag fragments on aggregates of Mytilus gal!oprovincia!is and their associated communities. A 4 week sea-exposure phase in the Rfa de Vigo with integrated plastic litter revealed significant effects of high amounts of fishing line on mussel respiration, along with marginally significant effects of high amounts of plastic litter, particularly fishing line, on the filtration capacity. Both effects are likely attributed to the plastic material preventing the mussels from fully opening their shells. There was also a marginal effect of the amount of plastic litter on the tridimensional complexity of the mussel aggregates, with mussel aggregates containing a low amount of plastic exhibiting the most complexity. These results fit with observations of how different aggregates were able to work with the plastic material, which future studies could help elucidate. I found no effects of the amount or shape of the plastic litter on total particulate matter collected within the mussel aggregates, on their body condition indices, nor on the species diversity or community composition of associated macrofauna. This study has the novel approach of using evidence-based hypothesis testing to demonstrate effects of plastic litter on higher organizational levels and for plastic materials to be categorized as hazardous, future studies should be carried out in this way.

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