Immediately after hatching, larvae of coral reef fish leave their natal reef environment and begin their planktonic dispersal phase, probably to avoid high predation on the reef. The time they spend in the open ocean before settlement (planktonic larval duration, PLD) varies from species to species and depends partly on developmental processes that eventually require re-settlement to a reef. The polyglutamine region (PolyQ) as part of the clock gene has been suggested as a possible candidate that could control developmental processes and potentially the time until settlement which can be determined by counting the rings of the otoliths. We studied the potential relationship between the number of glutamine repeats in 20 species of pomacentrids and their PLDs. Most pomacentrids came from similar locations, so we avoided the impact of latitudinal clines on PLD. Within the clock gene, we found two main distinguishable, variable glutamine-rich regions (PolyQ and Qrich). Considering phylogenetic relationships, PolyQ/Qrich repeat length and planktonic larval duration were significantly positively correlated. However, when analysing this relationship in a single species, the neon damselfish (Pomacentrus coelestis), we did not find a significant correlation between PolyQ length variation and PLD. Instead, we found a significant reduction of PLD in years with increased habitat availability. Our results show that glutamine-rich regions can influence the timing of colonisation on a broader scale, but that ecological factors - such as habitat availability - can also have a significant impact.

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 utilising 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 shown near the substratum when C. sivickisi medusae were absent. This can only be explained by the detection of polyps. Consequently, eDNA is an effective tool to detect both the medusae and polyps of cubozoans. This approach provides the means to reduce the risk of envenomation to swimmers and enhance our knowledge of cubozoan ecology.