FISHERY BULLETIN: VOL. 76, NO. 2 



Table 3.— Digestion efficiency and gross growth efficiency (K^) of marine zooplankton species obtained from laboratory experiments. 

 Methods of estimation are with radioactive isotopes ( '-"C, ^^P, and ^^S), elemental analyses (C, N, and P), calories, weight, and ratio 

 method of Conover (1966a). (Means in parentheses.) 



30i?/(70 - 30) = 0.75/?. 



(11) derived from the integrated form of Equation (12), 



Mortality Loss During Production 



Production calculated as in Equation (11) as- 

 sumes zero mortality. But production is always 

 accompanied by mortality, caused mainly through 

 predation by other animals and natural physiolog- 

 ical mortality. We considered only mortality from 

 the latter source.^ 



Assuming that 1 ml of oxygen is required to 

 combust about 1 mg of organic matter ( Jorgensen 

 1962), the instantaneous grow^th rate of zooplank- 

 ton is expressed as follows from Equations (1) and 

 (11), 



1,000 (W 



\-b. 



Wo'' 



^ )/(0.75(l - b)). (13) 



Chiba (1956) measured egg size in 55 species of 

 copepods. From his data and the body length- 

 weight relation of copepods developed by Krylov 

 (1968) the W^-.W ratio was calculated as 0.0001:1 

 to 0.01:1. A similar range of the ratios is also found 

 in the data of euphausiids, reviewed by Mauchline 

 and Fisher (1969). The lifespan of zooplankters 

 was defined arbitrarily as 1.5^ (duration of adult 

 stage is one-half that of the preadult). Daily mor- 

 tality (M) caused by the length of life span be- 

 comes 



dWIdt = (0.75/l,000)aW' 



(12) 



M = 24/(1.5^). 



(14) 



where W is body dry weight (milligrams) and t, 

 time (hours). The time required to grow from egg 

 (W(, in milligrams) to adult iW in milligrams) is 



^In addition to natural physiological mortality, molting loss by 

 copepods, the most dominant group in zooplankton community, 

 was included in the original calculations of Ikeda and Motoda 

 (1975). Here we ignore the molting loss because neither molting 

 intervals nor body size at molting were known. Therefore, pre- 

 sent production estimate (10-60 mg C/m^ per day) is slightly 

 higher than original one (9-57 mg C/m^ per day; Ikeda and 

 Motoda 1975). 



Total mortality ( M^^t) of the zooplankton commun- 

 ity in terms of percent of biomass is given in the 

 following equation: 



Mtot = 100(MiAW^i + M2f2W2 + . . . + MefeWe) 



^ifiWi + f2W2 + . . . + feWe) (15) 



where Mj, M^,    , M^ are daily mortalities of 

 zooplankters with body weight W^, W2,    , Wg, 



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