Does temperature and salinity limit asexual reproduction of Aurelia aurita polyps (Cnidaria: Scyphozoa) in the Gulf of Gdansk (southern Baltic Sea)? An experimental study

Outbreaks of the moon jellyfish Aurelia aurita occur seasonally in the Gulf of Gdansk (southern Baltic Sea), but field observations of sedentary polyps are scarce suggesting that asexual reproduction of scyphistomae is restricted in this water basin. This study has been set up to investigate the effects of temperature (3, 5, 10, 15, 20 and 25 degrees C) and salinity (2, 4, 7, 12 and 18 PSU) on polyp strobilation and budding under gradually changing exposure conditions. Duration and intensity of strobilation increased in low temperatures, while higher temperatures reduced (20 degrees C) and ceased (25 degrees C) production of ephyrae and enhanced budding activity. The asexual reproduction is therefore synchronized well with environmental conditions with strobilation occurring in spring and autumn/winter and growth of colonies (budding) taking place in summer. This provides a potential of scyphistomae to develop benthic colonies and support population size of medusae in the gulf. Salinity of 4 PSU caused absorption of tentacles and in 2 PSU, 100% mortality of polyps was observed indicating high sensitivity of scyphistomae to low salinity. An increase in water salinity induced more numerous strobilation as well as enhanced and longer budding suggesting that scyphopolyps can be more abundant in the more saline western Baltic.