ESTIMATED ZOOPLANKTON PRODUCTION AND THEIR 

 AMMONIA EXCRETION IN THE KUROSHIO AND ADJACENT SEAS 



TsuTOMU Ikeda' and Sigeru Motoda^ 



ABSTRACT 



Production and ammonia excretion of zooplankton in the Kuroshio and adjacent seas were estimated 

 from field data of biomass, size distribution, and habitat temperature of zooplankton, and from 

 experimental data of respiration and ammonia excretion rates as functions of body size and tempera- 

 ture. Winberg's basic balanced equations were applied to calculate production from respiration data. 

 Further, mortality related to the lifespan and the ratio of herbivores to carnivores in the zooplankton 

 community were estimated from theoretical assumptions. 



In this study, 18-72% of primary production was grazed by herbivorous zooplankton, and production 

 of herbivorous zooplankton ( = secondary production) was 10-60 mg C/m^ per day. The ecological 

 efficiency between primary and secondary production was 5-22%. Ammonia-nitrogen excreted by 

 zooplankton was 4-24 mg N/m^ per day, which can support 11-44% of the nitrogen requirements of 

 primary production. 



In marine ecosystems solar energy photosynthet- 

 ically fixed as oi'ganic matter by phytoplankton is 

 channelled through zooplankton to nektonic fishes 

 and crustaceans at higher trophic levels. Impor- 

 tant features of the roles of zooplankton in this 

 scheme are their extremely high conversion ef- 

 ficiency of phytoplankton organic matter (in con- 

 trast with terrestrial ecosystems, see Wiegert and 

 Owen 1971; Steele 1974) and the simultaneous 

 regeneration of nutrients through their excretory 

 activities. The latter role is considered an impor- 

 tant mechanism in maintaining constant primary 

 production levels in the seas, especially in oligo- 

 trophic areas (Ketchum 1962; Corner and Da vies 

 1971). 



These dynamic functions of zooplankton have 

 seldom been quantitatively evaluated in the field. 

 One difficulty lies in the fact that the zooplankton 

 community includes animals belonging to a vari- 

 ety of phyla and a number of species which differ 

 geographically. Information from detailed studies 

 on one or a few species is not adequate for this 

 purpose, and collection of all necessary data on 

 each component species in the community is not 

 practical. Therefore, the development of some al- 

 ternative approach is needed to overcome this 

 problem. 



^Australian Institute of Marine Science, P.M.B 3, Townsville, 

 MSO, Queensland, Australia. 



^Marine Science and Technology, Tokai University, Shimizu, 

 Japan. 



Manuscript accepted November 1977. 

 FISHERY BULLETIN; VOL. 76, NO. 2, 1978. 



METHODS 



In this study, we treat the zooplankton commun- 

 ity as an assemblage of different sizes of animals 

 and use body size-related constant functions for 

 respiration and ammonia excretion from labora- 

 tory experiments to estimate feeding, production, 

 and ammonia regeneration in the Kuroshio and 

 adjacent seas. A systematic survey of the study 

 area had been carried out by Japanese parti- 

 cipants in the CSK (Co-operative Study of the 

 Kuroshio and adjacent region) organized by 

 UNESCO during 1965-67 (Motoda et al. 1970; Irie 

 and Yamazi 1972). 



Biomass, Habitat Temperature, and Size 

 ( = Weight) Distribution of Zooplankton 



Zooplankton were sampled vertically from 150 

 m with a NORPAC standard net (mesh aperture, 

 0.35 mm) in summer (June-October 1965 and 

 1966) (Figure lA) and winter seasons 

 (December- April 1965, 1966, and 1967) (Figure 

 2A). From the average biomass of zooplankton 

 summarized by Yamazi (1971) for 0-150 m, the 

 present study area was divided into four density 

 classes (<10, 10-50, 50-100, and >100 mg wet 

 weight/m^). The isopleth for 100 mg wet weight/m^ 

 shifted northward in the cold season and south- 

 ward in the warm season, especially in the east 

 China Sea (Motoda et al. 1970; Irie and Yamazi 

 1972). Seasonal difference in the composition of 



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