Combined effects of ocean acidification and temperature on planula larvae of the moon jellyfish Aurelia coerulea

Rapidly rising levels of atmospheric CO2 have caused two environmental stressors, ocean acidification and seawater temperature increases, which represent major abiotic threats to marine organisms. Here, we investigated for the first time the combined effects of ocean acidification and seawater temperature increases on the behavior, survival, and settlement of the planula larvae of Aurelia coerulea, which is considered a nuisance species around the world. Three pH levels (8.1, 7.7 and 7.3) and two temperature levels (24 °C and 27 °C) were used in the present study. There were no interactive effects of temperature and pH on the behavior, survival, and settlement of planula larvae of A. coerulea. We found that the swimming speed and mortality of the planula larvae of A. coerulea were significantly affected by temperature, and low pH significantly affected settlement. Planula larvae of A. coerulea from the elevated temperature treatment moved faster and showed higher mortality than those at the control temperature. The settlement rate of A. coerulea planulae was significantly higher at the pH level of 7.3 than at other pH levels. These results suggest that seawater temperature increase, rather than reduced pH, was the main stress factor affecting the survival of A. coerulea planulae. Overall, the planula larvae of the common jellyfish A. coerulea appeared to be resistant to ocean acidification, but may be negatively affected by future seawater temperature increases.