Jellyfish are widely distributed throughout the world’s oceans. However, understanding jellyfish species’ distributions remains poor. Here, we addressed this knowledge gap by applying an approach that uses citizen science observations to inform collection of samples which then undergo molecular analysis. Doing so allowed us to confirm the presence of the jellyfish Cyanea purpurea in the waters of Hong Kong SAR for the first time. Due to morphological overlap in Cyanea species, DNA analysis confirmed specimen identification. Samples were taken from 19 jellyfish individuals for subsequent DNA analysis. Ten samples (53%) were confirmed as C. purpurea, two samples (10%) were identified as Cyanea nozakii, and seven samples (37%) were not able to be identified. The combined application of citizen science and DNA analysis has proven effective in confirming the presence of C. purpurea in Hong Kong waters. This approach of using citizen science observations to inform the collection of samples for subsequent molecular analysis could be transferrable to other similar situations in which identification based solely on morphology is insufficient, potentially enhancing our ability to recognise species occurrence.