FISHERY BULLETIN: VOL. 72. NO. 2 



Table 13. — Seasonal variation of the mean rate of net produc- 

 tion per day (NPtn is in mg organic matter rii^ day"') for postlar- 

 va\ Pleurobrachia bachei at stations located 1.6 km from shore in 

 La Jolla Bight. The mean annual net production is given as the 

 sum of the mean rate per day multiplied by the appropriate time 

 interval, A <; the variance of the mean annual net production is 

 also given. Note that the sum is for 0.956 yr. 



sevenfold lower than that at station 5 (1.6 km off 

 Scripps Institution) and fivefold lower than the 

 mean for all stations located 1.6 km from shore. 

 For these comparisons, the production at station 6 

 was extrapolated to 0.956 yr. The net production of 

 larvae and eggs at station 5 contributed only 

 about 3% of the sum of net production of eggs, 

 larvae, and postlarvae at that station. 



For stations 1,3, and 5 the annual mean ratio of 

 the net production per day of postlarvae to their 

 mean daily standing stock (B, of Equation (2)) are 

 0.197, 0.196, and 0.211, respectively. The mean 

 ratios are based on 32, 43, and 54 observations for 

 stations 1, 3, and 5, respectively. There are no 

 significant differences between the variances 

 (F-ratio tests) of all paired contrasts of stations 

 (P>0.05). There are no significant differences be- 

 tween all paired contrasts of station means 

 (P>0.50). The overall annual mean ratio at these 

 three stations is 0.202, with 95% confidence limits 

 for the mean being 0.187-0.217. Thus, the ratio of 

 production to biomass on the day of maximal pro- 

 duction was no greater than the annual mean. 



In order to estimate the food chain efficiency 

 (defined for any trophic level L as the steady state 

 ratio of yield to predators at level L -I- 1 to the net 



production of trophic level L-1) of the transfor- 

 mation of materials or energy by trophic levels, 

 the two parameters stated above must be known: 

 1 ) the net production of potential food at level L-1 

 and 2) the yield to predators from the level L, 

 which in steady state is the total net production of 

 level L minus losses to decomposers. This concept 

 can be extended to include more than three trophic 

 levels, e.g., the square root of the ratio of ingestion 

 by secondary carnivores to net primary production 

 might be termed the equal transfer efficiency of 

 herbivores and primary carnivores. 



In practice it is very difficult to accurately 

 "measure" the secondary production of the entire 

 herbivore trophic level in the sea, and such data 

 are not available in my study area. Further, the 

 estimates of net production by P. bachei could not 

 be partitioned into the fractional losses to decom- 

 posers and as yield to predators. Therefore, two 

 simplifying assumptions were made in calculat- 

 ing the transfer efficiency for the macrozooplank- 

 ton of La Jolla Bight: 1 ) all of the net production by 

 P. bachei resulted in yield to predators and none to 

 decomposers and 2) the efficiency was constant 

 and equal from the primary producer level 

 through the first-order carnivore level of P. 

 bachei. Given these limiting assumptions, the 

 efficiency calculated is referred to as the "equal 

 transfer efficiency." Thus, if net production data 

 were not available for trophic levels between 

 primary producers and the trophic level of in- 



Table 14. — Summary of "annual" net production (ANP) values 

 (in mg organic matter in^ time"') of Pleurobrachia bachei, at four 

 stations in La Jolla Bight. The value at station 6 is for 0.84 yr; all 

 other values are for 0.956 yr. The standard deviation of ANP for 

 each respective value is also given. Values are for postlarvae 

 unless otherwise specified. The mean production for larvae and 

 eggs at stations 1-5 were calculated assuming that the same 

 fraction of production would be as larvae and eggs at all stations 

 as at station 5. 



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