MEPS prepress abstract  -  DOI:

Strobilation of three scyphozoans (Aurelia coelurea, Nemopilema nomurai and Rhopilema esculentum) in the field at Jiaozhou Bay, China

Song Feng*, Shi-Wei Wang, Song Sun**, Fang Zhang, Guang-Tao Zhang, Meng-Tan Liu, Shin-ichi Uye


ABSTRACT: Studies of strobilation of scyphozoan polyp populations in the field are essential for determination of the natural seasonal period of ephyra release and for predicting the size of medusa populations, but they rarely have been conducted. In this study, we set up experimental polyp colonies of three scyphozoans (Aurelia coerulea, Nemopilema nomurai and Rhopilema esculentum) on settling plates in Jiaozhou Bay, China, and monitored them at 2–7 day intervals for 8 months from December 2012 to August 2013. Polyps of A. coerulea survived, even proliferating by budding during the entire period, while those of N. nomurai and R. esculentum experienced high mortality and died out after strobilation. Strobilation in all three occurred from late winter to early summer, but the exact timing, duration, frequency, strobilation percentage and disc numbers per strobila differed by species. Aurelia coerulea started strobilation earliest, on February 25 (temperature: 3.9°C), and persisted for 105 days until June 9 (18.1°C). Nemopilema nomurai strobilated from March 28 to June 9 (temperature range: 6.4–18.1°C), and with some performing a second, less conspicuous strobilation from May 6 to June 9 (12.0–18.1°C). Rhopilema esculentum strobilated last, from April 15 to July 8 (9.0–21.5°C). Greater polyp population resilience in A. coerulea over N. nomurai and R. esculentum can be attributed, at least in part, to persistent propagation by budding. That may facilitate the annually recurring medusa blooms of A. coerulea observed in the region. The latter two species may give rise to medusa blooms only when their vulnerable polyps have survived well. Due to the later strobilation, R. esculentum ephyrae may be susceptible to competition for food with and predation by post-ephyra stages of A. coerulea and N. nomurai