Marine organisms are naturally exposed to multiple environmental drivers and stressors due to the highly dynamic nature of the marine habitats in which they live. Anthropogenic activities have, in some cases, exacerbated these natural drivers, as with climate-change induced water temperature increase, or added novel stressors, such as the ingestion of microplastic pollution. The ability of marine organisms to tolerate combined drivers and stressors, from a physiological to ecological level, will greatly affect the distribution, functioning, and survival of populations, and is in general a poorly understood subject despite its vital importance. In this study, a chronic exposure experiment will be performed using a replicated multi-stressor mesocosm setup, examining the individual and combined impacts of increased water temperature (+3.1 oC), and environmentally-relevant suspended microplastic concentrations (10µm size, 50 MP l-1). The European flat-oyster (Ostrea edulis Linnaeus 1758) was selected for this study due to it being of both conservation and commercial importance, and, as a sessile filter-feeding bivalve, is greatly susceptible to exposure to both of these stressors. Six hundred adult O. edulis will be exposed to four different treatments consisting of increased temperature, increased MP, both stressors, or neither, for 200 days. Haemolymph, tissue, and whole organism samples will be taken throughout the exposure, for analysis of a wide range of biochemical and physiological functions, and quantification of MP retention. Growth, clearance and egestion rates, respiration and mortality will be recorded for each treatment. Variations in MP dynamics will be monitored, as will the biodeposition rates of the oysters themselves. The large time series dataset generated from this exposure study, covering a broad range of biotic and abiotic metrics, will provide a better understanding of the effects of MP ingestion by bivalve molluscs in both the current climate and under future conditions.