The worlds’ oceans are increasingly exposed to a diversity of contaminants which stem from anthropogenic activities, many considered to be ‘contaminants of emerging concern’ (CECs). For several CECs, their influence on marine ecosystems is unknown. Historically, biomonitors have been used as an effective time-integrated tool to monitor contaminant loads in ecosystems. The upside-down jellyfish (Cassiopea) is showing promise as a biomonitor of a range of marine contaminants. I will be utilising this species to assess the effect of a number of emerging contaminants on the jellyfish and its endosymbionts. Using manipulative laboratory experiments, Cassiopea will be exposed to a range of contaminants including microplastics, petroleum hydrocarbons and organic UV filters to assess their response to chronic exposure. Changes in jellyfish size, photosynthetic efficiency, and endosymbiont zooxanthellae density will be easured as sub-lethal responses to contaminant exposure. The results from this study will be summarised and the relative toxicities of the respective contaminants discussed. Findings from this research will also determine the effectiveness of Cassiopea as a biomonitor to a range of emerging contaminants in coastal marine systems.