Abundance and biomass of scyphomedusae, Aurelia aurita and Chrysaora melanaster, and Ctenophora, Bolinopsis mikado, with estimates of their feeding impact on zooplankton in Tokyo Bay, Japan |
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| Authors: | Junji Kinoshita Juro Hiromi Yoshiaki Yamada |
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| Institution: | (1) College of Bioresource Sciences, Nihon University, Kameino, Fujisawa 252-8510, Japan;(2) Kanagawa Prefectural Fisheries Research Center, Misakicho-jogashima, Miura 238-0237, Japan;(3) Present address: Sagami Bay Experimental Station, Kanagawa Prefectural Fisheries Research Center, Hayakawa, Odawara 250-0021, Japan |
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| 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. |
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| Keywords: | Aurelia aurita Bolinopsis mikado abundance feeding impact Tokyo Bay |
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