Irukandji jellyfish distributions at Ningaloo Reef: spatial and temporal patterns of Malo bella (Cubozoa) environmental DNA

The cubozoan jellyfish Malo bella can cause Irukandji syndrome, yet little is known about its ecology or distribution. We examined its spatiotemporal distribution along Western Australia’s Ningaloo Coast using a species-specific quantitative PCR (qPCR) assay to detect environmental DNA (eDNA). Based on anecdotal information, we hypothesised that eDNA would vary intra-annually and be more likely in the open ocean than nearshore. Over 3 years, eDNA was sampled 15 times at 12 sites spanning 4 distances from shore (lagoon, reef slope, intermediate, offshore). Sampling occurred across multiple months from April to December in 2021 to investigate intra-annual variability, then from March to July 2022 and April to June 2023 to target months with peak abundances. Detections per water sample (out of 6 qPCR replicates) and eDNA concentrations (copies per reaction) were analysed using generalised linear mixed models. Detections and concentrations were greater at open ocean than nearshore sites on 13 of 15 sampling dates; however, on 2 dates, they were greater nearshore. Inter- and intra-annual variation was evident, with greatest detections in 2021 and from April to June. In 2021, detections persisted from March to September, indicating a longer Irukandji season than predicted. These findings demonstrate eDNA’s value for monitoring hazardous jellyfishes and highlight variability in cubozoan spatiotemporal patterns: M. bella contrasts with other Australian cubozoans, which generally occur nearshore and in warmer months. Future research into the broader range and life history characteristics of M. bella , along with environmental drivers of its presence, will improve ecological understanding and risk management.