Journal of Oceanography, Vol. 62 (No. 5), pp. 607-615, 2006
Junji Kinoshita1*, Juro Hiromi1 and Yoshiaki Yamada2
1College of Bioresource Sciences, Nihon University, Kameino, Fujisawa 252-8510, Japan
2Kanagawa Prefectural Fisheries Research Center, Misakicho-jogashima, Miura 238-0237, Japan
(Received 7 February 2005; in revised form 24 April 2006; accepted 24 April 2006)
Abstract: The abundance of a scyphomedusae, Aurelia aurita and Chrysaora melanaster, and a ctenophore, Bolinopsis mikado, in Tokyo Bay was investigated from 1995 to 1997. Aurelia aurita appeared throughout the year with a peak in abundance occurring from spring to summer. The average abundance and biomass during this period for the three successive years was 4.8, 43.8 and 3.2 ind. m-2, and 1.02, 10.0 and 0.42 gC m-2, respectively. The values in 1995 and 1997 were comparable with those previously reported for A. aurita abundance from 1990 to 1992. Values were very high in 1996, but the size composition of the bell diameter did not differ from other years, which suggested the absence of food limitation for A. aurita in 1996. C. melanaster was scarce over the survey period (<1.0 ind. m-2) while Bolinopsis mikado was more abundant during September to December, with maximum values of 172 ind. m-2 and 0.33 gC m-2 observed in December 1997. The weight-specific clearance rate for A. aurita on zooplankton (mainly copepods and their nauplii) was 0.16 ± 0.05 lgWW-1 h-1 (n = 13). Population clearance rate peaked from spring to summer, with average levels of 14.2%, 162% and 5.0% day-1 obtained from spring to summer for respective years. Population clearance rates for B. mikado, calculated based on minimum carbon requirements, was 7.1% day-1 in December 1997. Consequently, the trophic role of gelatinous zooplankton as predators in Tokyo Bay is important all the year round, considering the high impact of A. aurita from spring to summer and B. mikado from autumn to winter.