Effects of temperature and salinity on the asexual reproduction of Aurelia coerulea polyps

Aurelia coerulea polyp is an important stage in the outbreaks of this species. To test the combined effects of salinity and temperature on the survival and asexual reproduction of polyps, we maintained 864 polyps at various salinities (15, 25, 33, and 40) and temperatures (9, 12, 15, 18, 21, and 24°C). Polyps could mostly survive in all treatment combinations except in salinity 15 treatments with low temperatures (9–15°C). Budding occurred at all temperatures (9–24°C), while strobilation only occurred at the low temperatures (9–15°C). The range of 12–15°C was suitable for strobilation and ephyrae release. The optimal range of salinity for asexual reproduction was 25–33. Low (15) or high (40) salinity could significantly reduce the numbers of new buds or ephyrae, and low salinity of 15 retarded and even prevented strobilation at low temperatures. The optimal treatment for budding and strobilation was 21°C-salinity 25 and 12°C-salinity 33, respectively. Salinity had less of an impact than temperature on asexual reproduction, except for the polyps in high or low osmotic pressure conditions.