Extreme changes in salinity drive population dynamics of Catostylus mosaicus medusae in a modified estuary

Modifications to estuaries through the construction of barrages alter natural dynamics inhabitant species by controlling freshwater inputs into those systems. To understand effects modified flows on a native scyphozoan jellyfish, Catostylus mosaicus, and identify environmental drivers medusa occurrence, we analysed 20-year observational dataset composed 11 variables presence/absence from 15 sampling stations located below Fitzroy Barrage, in River, Queensland. Major decreases salinity (minimum 0) occurred approximately 16 times during period medusae disappeared estuary following every major flow event. Salinity was identified as most influential variable contributing variation number upper sites reporting jellyfish. We then ran two laboratory experiments test hypotheses: (i) prolonged impair survival, pulsation, respiration rates C. mosaicus medusae; (ii) transient temporarily pulsation but recover when returns normal levels. Medusae were unable survive extended periods at extreme low salinities, such that they would experience barrage opens fully, had significantly higher survival recovery smaller, changes might occur moderate rainfall This demonstrates for first time modification regulates population an estuarine highlights need robust, long term datasets, firmly embed experimental approaches realistic ecological contexts.