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, has shown promise as a biomonitor to a range of contaminants, including heavy metals and pesticides. Using manipulative laboratory experiments, Cassiopea was exposed to organic ultraviolet (UV) filters. Both the jellyfish and endosymbionts response to chronic exposure was assessed. Changes in jellyfish size, photosynthetic efficiency, and endosymbiont zooxanthellae density was measured as sub-lethal responses to contaminant exposure. The results from this study will be summarised and the relative toxicities of the organic UV filters discussed. Findings from this research will help determine the effectiveness of Cassiopea as a biomonitor to organic UV filters found in coastal marine systems.