IKEDA and MOTODA: ZOOPLANKTON PRODUCTION AND AMMONIA EXCRETION 



Table 1. — Analysis of body size distribution of zooplankton in 

 the Kuroshio and adjacent seas from a normalized catch dis- 

 tribution curve. Warm season (June-October): /x = -0.8033, SD 

 = 0.2856; cold season (December-April): m = -0.7350, SD = 

 0.3705. The interval of /u ± 3 SD of the normal curve was equally 

 divided by the SD class intervals ( 1-6), and median value in each 

 class interval was taken as the representative body size 

 [W\ -We) for that class interval. 



1.5, and 2.5. Then, total respiration (R ^^^) and total 

 ammonia excretion rates (.£,„,) became 



tot' 



-'^tot - -R/i + -^2/2 + • • • + ^eA 



6/6 



'tot 



EJ, +EJ,+ ... + EJ, 



(3) 



(4) 



where i?i, R2, . .  , Rq and E^, E.2, . . . ,Eq are the 

 respiration rates and ammonia excretion rates of 

 zooplankton with body weight W^, W2, . .  , Wg, 

 respectively, and fi, [2, . . . , A are respective 

 theoretical frequencies ( = individual number) in 

 each weight category. A wet weight:dry weight 

 conversion factor of 10 was assumed (Wiebe et al. 

 1975). Frequency /"j, /"o, . . . , /"e of a given zoo- 

 plankton biomass (XW) was calculated by multi- 

 plying/'/ 1 W/! To facilitate calculation, respiration 

 and ammonia excretion rates per unit biomass of 

 zooplankton characterized by the size distribution 

 curve in warm and cold seasons were computed as 

 functions of habitat temperature (Table 2). Respi- 

 ration was expressed as carbon units assuming 

 RQ = 0.8 (protein metabolism). 



Feeding and Production Estimates 

 From Respiration 



Winberg ( 1956) proposed the following basic bal- 

 anced equations for fishes: 



0.8F =P + R 

 K, =P/F -100 

 K^ =P/(0.8F)100 



(5) 

 (6) 



(7) 



where F is feeding; P, growth (= production); R, 

 respiration; K-^, gross growth efficiency; K2, net 



Table 2. — Respiration and ammonia excretion rates per unit 

 biomass of zooplankton in warm (June-October) and cold 

 (December- April) seasons as derived from calculations in the 

 text. 



Habitat 

 temp (=C) 



Respiration rate 

 (^g C/mg dry wt per h) 



Ammonia excretion rate 

 (^lq N/mg dry wt per ti) 



5 

 10 

 15 

 20 

 25 



growth efficiency; and 0.8, digestion efficiency for 

 fishes. From these equations F and P are derived 

 by knowing R and K^, 



F = 100/?/[0.8(100 - K2)] = 100i?/(80 - K^) (8) 



P = K^RiaOO 



K^) = K,R/(80 - K^). (9) 



Apparently both digestion efficiency and gross 

 growth efficiency {K^) of marine zooplankton dif- 

 fer to a great degree, not only among zooplankton 

 species but also within a single species (Table 3). 

 Marshall and Orr ( 1955a) observed that the diges- 

 tion efficiency of Calanus finmarchicus changed 

 with a variety of food phytoplankton species 

 offered. Apparently K^ can be affected by de- 

 velopmental stages (Mullin and Brooks 1970b; 

 Paffenhofer 1976; Harris and Paffenhofer 1976), 

 feeding rate ( Mullin and Brooks 1970b; Harris and 

 Paffenhofer 1976), kinds of food (Paffenhofer 

 1976), and method of estimation (Butler et al. 

 1969, 1970). Moreover, both quality and quantity 

 of foods used in these experiments are not neces- 

 sarily the same as those that zooplankton will 

 meet in the field. Although we have little informa- 

 tion about the exact nature of foods of zooplankton 

 in the field, their digestion efficiency is assumed to 

 be quite high, because zooplankton have an ability 

 to select suitable foods (Lasker 1966; Marshall 

 1973). The value of /Cj has a tendency to increase 

 with a decrease in food concentration (Mullin and 

 Brooks 1970a; Harris and Paffenhofer 1976). In 

 the field, food concentration is much lower than in 

 laboratory experiments so that a higher /^i value 

 would be expected. 



For these reasons we finally chose values of 70% 

 for digestion and 30% for K^ as realistic values of 

 zooplankton in the field, regardless of species and 

 food habit. Then, Equations (8) and (9) for fishes 

 were rewritten for zooplankton, as 



F = lOORKlQ - 30) = 2.bR (10) 



361 



