Validation of eDNA as a viable method of detection for dangerous cubozoan jellyfish

Abstract Stings from certain species of cubozoan jellyfish are dangerous to humans and their seasonal presence in tropical marine waters poses a significant risk to coastal communities. The detection of cubozoans is difficult due to high spatial and temporal variation in their occurrence and abundance. Environmental DNA (eDNA) has the potential to detect rare species and therefore offers potential to detect cubozoans, not only pelagic medusae, but presence of cryptic polyp life stages. The objective of this study was to validate the use of eDNA as a viable detection method for four cubozoan species ( Chironex fleckeri , Copula sivickisi , Carybdea xaymacana, and Carukia barnesi ). Species‐specific primers were developed for each of these four cubozoans and an eDNA approach validated utilizing both laboratory and field trials. Laboratory DNA degradation experiments demonstrated that C . sivickisi DNA degraded quickly but could still be detected in sea water for up to 9 days post‐jellyfish removal. Positive detection was found for C . fleckeri , C. xaymacana, and C. sivickisi medusae in the waters surrounding Magnetic Island, Queensland, in the Austral spring/summer (September‐January). Based on visual surveys, there was a poor relationship between concentration of eDNA and abundance of jellyfish. Positive eDNA amplification was also found from water sampled near the substratum when C. sivickisi medusae were out of season and absent. This suggests the eDNA analysis was likely detecting C. sivickisi polyps located within the substratum. Consequently, eDNA is an effective tool to detect both the medusae and likely polyps of cubozoans. This approach provides the means to reduce the risk of envenomation to swimmers and enhance our knowledge of cubozoan ecology.