Filter-feeding bivalves, such as the blue mussel, Mytilus edulis, provide important ecosystem services within coastal ecosystems. Amongst them is the control of phytoplankton abundance and species composition while also contributing to nutrient cycling, which can diminish the impacts of coastal eutrophication and Harmful Algal Blooms (HAB), two major stressors of coastal environments. However, the healthy functioning of mussels and the provisioning of related ecosystem services can in turn be

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... mpromised by coastal anthropogenic pressures. This thesis focuses on the effects of two prevailing forms of coastal pollution: microfibers and artificial light at night (ALAN) on coastal ecosystem services provided by mussels. Microplastics (<5mm) are found at coastal ecosystems around the world and their impact on marine organisms has been investigated by multiple studies therefore an initial review of literature on the effects of microplastic pollution on coastal bivalves was conducted. The review aimed to assess whether the experimental settings employed in laboratory studies are relevant to field observations on microplastics characteristics and concentrations. This investigation revealed that previous studies have used a wide range of shapes, materials, sizes, and concentrations of microplastics; and in many cases, these did not coincide with the characteristics of microplastics found in coastal waters. For instance, the concentrations of microplastics used were frequently orders of magnitude higher than environmental levels. Moreover, 48.5% of studies exposed bivalves to spherical microplastics, whereas in the field, fibres were the prevailing shape. Despite the prevalence of microfibers in the coastal marine environment, the review revealed that research on the effects of microfibers on bivalves is scarce. To fill this gap in literature and enhance our understanding on the impacts of microfibers on the phytoplankton consumption by bivalves, a short-term experiment was performed simulating acute microfiber concent [...]