抄録
Biomass and body elemental composition of the giant jellyfish Nemopilema nomurai in the southwestern Japan Sea were studied using specimens collected with mid-water trawl nets during September and October 2006, 2007, and 2009. The average biomass of N. nomurai was calculated as 0.26–0.93 g wet weight (WW) m−3. Body elemental composition of N. nomurai was water=95.8% of WW, carbon=6.6% of dry weight (DW), nitrogen=1.7% of DW, and phosphorus=0.14% of DW. Carbon requirements for growth and respiration were estimated in per unit area using biomass data. For growth analysis, size-frequency distributions of bell diameter (BD) were examined from specimens collected using set-nets in Wakasa Bay during August–January in 2005–2007 and the growth rate was calculated as 1.5 cm d−1. For growth production, individual daily increase of total body weight derived from BD growth was summed for populations collected with mid-water trawl nets. Respiratory oxygen consumption in N. nomurai was estimated from electron transport system activity as 8.4 µLO2 gWW−1 h−1 at 20°C. Based on these values, the carbon requirement for growth and respiration was predicted as 0.1–0.33 mgC m−3 d−1. Biomass and carbon requirement data of N. nomurai were compared to the biomass of the common squid Todarodes pacificus and copepod production, respectively, in the Japan Sea. In the present study, it was demonstrated that when mass incidences of N. nomurai occurred in the Japan Sea, the biomass of N. nomurai was substantial and equivalent to that of the common squid. The amount of zooplankton consumed as prey by N. nomurai was not large enough to influence the biomass of zooplankton as a whole; however, it was critical for dense aggregations in a small area.
