Effects of copper and reduced salinity on the early life stages of the moon jellyfish Aurelia coerulea

The moon jellyfish Aurelia coerulea is a nuisance species around the world, and is considered highly tolerant of a wide range of environmental conditions. The recruitment success during the early life stages of scyphomedusae can have a major effect on the abundance of the adult medusa population and can contribute to jellyfish blooms. The environmental stress factors of elevated copper concentrations and reduced salinity often act simultaneously during the summer time. In this study, we investigated the combined effects of three concentrations of copper (0, 10 and 25 μg L ⁻¹ ) and reduced salinity (from ambient 31 psu to 22 psu) on the early life stages of A. coerulea. We found that the swimming speed of the planula larvae of A. coerulea was significantly affected by the copper concentration. Planula larvae of A. coerulea from the highest copper concentration (25 μg L ⁻¹ ) moved slower at than at lower copper concentrations. The results showed significant interactive effects between copper concentrations and salinity on the settlement of A. coerulea planulae. High copper concentration (25 μg L ⁻¹ ) and reduced salinity (22 psu) significantly increased the settlement of A. coerulea planulae. Additionally, copper concentration had a significant effect on the asexual reproduction rate of A. coerulea polyps, which was significantly higher at the moderate copper concentration (10 μg L ⁻¹ ). These results suggest that the current concentration of copper was not a stress factor for the early life stages of A. coerulea and may potentially stimulate population increases of A. coerulea in Chinese coastal waters.