Combined effects of food supply and temperature on asexual reproduction and somatic growth of polyps of the common jellyfish Aurelia aurita s.l.

The polyp stage is an important part of the Aurelia aurita s.l. life cycle, because polyp clones are able to increase their population size by budding, providing the opportunity to increase the medusa population by the produc- tion of many ephyrae through strobilation. We investigated asexual reproduction of A. aurita polyps on an individual basis at 4 different temperatures (i.e. 18, 22, 26 and 28 o C) and at 5 different food levels (i.e. 1.7, 3.3, 6.6, 10 and 13.3 mg C polyp �1 d �1 ) in the laboratory. Three types of asexual reproduction were observed: polyps directly budded from the parent stalk (DBP), polyps budded from the parent pedal stolon (SBP), and podocysts (PC). DBP was the major repro- ductive method (94% of the total) and SBP and PC accounted for only 5 and 1%, respectively. PC were produced by the polyps kept under low food supply (�3.3 mg C polyp �1 d �1 ) and high temperature (�26°C). Production of new polyps by DBP and SBP significantly increased with increasing food and temperature. The somatic growth of parent polyps significantly increased with more food and cooler temperatures. We conclude that both increases in water temperature through global warming and increases in abundances of zooplankton prey because of eutrophication may be responsible for the prominent blooms of A. aurita medusae in East Asian coastal waters in recent times.