IK EDA and MOTODA: ZOOPLANKTON PRODUCTION AND AMMONIA EXCRETION 



Table 4. — Daily mortality related to the lifespan of zooplankton 

 in warm (June-October) and cold (December-April) seasons as 

 derived in the text. 



respectively. For Mjot as a function of habitat 

 temperature and W ^-.W ratio (0.0001:1, 0.001:1, 

 and 0.01:1) see Table 4. 



Ratio of Herbivores to Carnivores in 

 Zooplankton Community 



Although zooplankton include both herbivores 

 and carnivores, this distinction of food habits is 

 probably of little importance regarding ammonia 

 excretion by zooplankton. However, the difference 

 is essential when production is considered, espe- 

 cially secondary production. 



We assumed that the zooplankton community at 

 any trophic level is represented by a similar size 

 distribution, same digestion efficiency (70%) and 

 same K^ value (30%). Assuming that the daily 

 production of herbivores (0.75aSW, {b^lBQ)BQ) 

 equals the daily consumption by the primary car- 

 nivores (2.5a IW, (b,/Bi)5i) (derived from Equa- 

 tions (1), (3), (10), and (ID) the relation can be 

 simplified to 



5i = (0.75/2. 5)fi( 



16) 



where Bq and B^ are the total number of herbi- 

 vores and primary carnivores, respectively, in a 

 community, and b, is the number of zooplankters 

 of a given body size. Assuming that the daily pro- 

 duction of carnivores in the lower trophic level is 

 equal to the daily feeding of carnivores at the next 

 trophic level, the number of carnivores at trophic 

 level n becomes 



B, 



(0.75/2.5)"Bo 



(17) 



The total number of zooplankters from the pri- 

 mary carnivore level to the carnivore trophic level 

 n becomes 



If the number of trophic levels of carnivores is 

 simply taken as 2, then the number of primary and 

 secondary carnivores can be calculated to be 



Bi +B2 = 0.39Bo- 



This value does not differ greatly from the value 

 obtained when an infinite number of carnivorous 

 trophic levels are considered 



B, 



+ B2 + 



+ B, 



0.43Br 



Therefore, the value 0.4:1 seems appropriate for 

 the ratio of numbers of carnivorous zooplankton to 

 all herbivorous zooplankton. 



RESULTS AND DISCUSSION 



Distribution of estimated production of her- 

 bivorous zooplankton (i.e., secondary production) 

 is summarized for warm and cold seasons in Fig- 

 ures IB and 2B. Table 5 summarizes our estimates 

 for grazing, production, and natural physiological 

 mortality of herbivorous zooplankton and 

 ammonia-nitrogen excretion of zooplankton (her- 

 bivores plus carnivores). 



Production 



The present use of Winberg's balanced equa- 

 tions to estimate productivity (growth) from data 

 on respiration is not new. Shushkina (1968) esti- 

 mated the production of the copepod, Haloptilus 

 longicornis, in the Fiji Sea from an indirectly cal- 

 culated respiration rate for this species and K^ 

 values from the literature including zooplankton 

 species. In order to determine whether zooplank- 

 ton in the field were supplied adequate food, we 

 used a set of values for digestion efficiency, and 

 gross growth efficiency (K^), instead of a single 

 value of net growth efficiency {K2), to obtain feed- 

 ing requirements and production simultaneously 

 (which is not possible when K^ is used, see Equa- 

 tion (8)). When the feeding requirements of zoo- 

 plankton exceed food availability (i.e., food short- 

 age), any estimate of production from Winberg's 

 equation is unrealistic. However, our data indi- 

 cate that feeding requirements of herbivorous 

 zooplankton was 18-72% of primary production 

 (Table 5). 



Bi + B2 + ... + B„ = Bo((0.75/2.5) + (0.75/2.5)^ + . . . + (0.75/2.5)") 



= Bo ((0.75/2.5) (1 - (0.75/2.5)" ))/(l - 0.75/2.5). 



363 



