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

通过建造拦河坝对河口进行改造，可以通过控制向这些系统中输入的淡水来改变居民物种的自然动力。要了解改良的淡水流量对原生海鞘水母Catostylus mosaicus的影响为了确定水母发生的环境驱动因素，我们分析了一个为期20年的观测数据集，该数据集由11个环境变量和水母的存在与否组成，这些数据来自昆士兰州菲茨罗伊河下菲茨罗伊弹幕下方的15个采样站。在20年期间，盐度出现了重大下降（最低盐度为0），发生了大约16次，在每次大型淡水流量事件发生后，美杜莎从河口消失了。盐度被认为是最有影响力的变量，导致报告水母的上河口站点数量发生变化。然后，我们进行了两个实验室实验，以检验以下假设：（i）盐度的持续下降会损害花叶念珠菌的存活，搏动和呼吸速率水母 （ii）暂时减少暂时损害搏动和呼吸，但在盐度恢复到正常水平时美杜莎会恢复。美杜莎无法在盐度极低的情况下长时间生存，因此当弹幕完全打开时它们会经历，但是在中等降雨事件发生后盐度发生较小的瞬时变化后，其存活率和恢复率显着提高。这首次证明了拦河坝对淡水流量的调节调节了河口水母的种群动态，并突显了对强大，长期数据集的需求，并牢固地将实验方法嵌入现实的生态环境中。