Standing Crops and Trophic Levels— Blackburn 
53 
those for Z or H on C, as noted above, whether 
or not steady-state conditions prevail For the 
material of Table 1, D (equation [6}), where 
fsm.c is significant, the point estimate is 1.075 
with 95% confidence limits 0.099 to 1.731. For 
the material of Table 1, A and B, the following 
eight point estimates are available from various 
regressions noted above: 0.701, 0.799? 0.952, 
1.025, 1.054, 1.077, 1.091, and 1.128. They dif- 
fered in n, in the independent variable (Z or 
H ) , in the basis of point-grouping for Bartlett’s 
line-fitting method, and in the significance of 
the partial correlation coefficient. It may be con- 
cluded that the standing crop of primary carni- 
vores generally varies in an approximately linear 
way with that of herbivores, when there is a 
significant relationship between them, whether 
or not steady-state conditions exist among all 
standing crops. This means that primary carni- 
vores utilize herbivores with about the same 
efficiency at different levels of herbivore stand- 
ing crop. 
The positions of the regressions are not nearly 
as informative as their slopes, for methodological 
reasons given above, but a few interesting com- 
parisons of the means of paired variables can 
be made. Standing crops of chlorophyll a and 
copepods can be .estimated very approximately 
in terms of a common unit, mgC/m 3 . For AB- 
36-H the mean crop of chlorophyll a is 18.40 
mg/10 2 m 3 in the upper 100 m, and the mean 
of copepods (free of interstitial water) is 2.94 
ml/10 3 m 3 in the upper 300 m. The latter, con- 
verted as in Appendix I, becomes 5.00 ml/ 
10 3 m 3 in the upper 140 m, and it is assumed 
for the present purpose that the same concentra- 
tion exists in the upper 100 m. The mean 
amounts of chlorophyll a and copepods per cubic 
meter in the upper 0-100 m are then 0.184 mg 
and 0.005 ml The latter may be taken as 0.640 
mg dry weight, using the ratio of 128 mg/ml 
given by Tranter ( I960) for warm-oceanic zoo- 
plankton, predominantly copepods, free of in- 
terstitial water when measured by volume. The 
corresponding weights of carbon per cubic meter 
are estimated as 5-52 mg for the phytoplankton 
(multiplying weight of chlorophyll a by 30, after 
Strickland, I960) and 0.24 mg for the copepods 
(considering carbon as 38% of dry weight, fol- 
lowing Curl, 1962). The ratio, copepod C/plant 
C, is then 0.043; it would, of course, be much 
higher for total-herbivore carbon or zooplankton 
carbon. It is a very rough estimate. For instance, 
a higher factor than 30, e.g., 60, could have been 
used to estimate C from chlorophyll a ( Strick- 
land, I960), and the concentration of copepods 
could be higher in the upper 100 m than in the 
upper 140 m (Thrailkill, 1956); either of these 
could affect the ratio, although both together 
might not change it much. For AB-8-H the 
same procedures give values of 7.58 and 0.28 
mgC/m 3 , with ratio 0.037. 
The standing crops of zooplankton and car- 
nivorous micronekton cannot be expressed 
realistically as carbon, because of taxonomic 
heterogeneity and interstitial water. They can be 
compared in ml/ 10 3 m 3 , with many reservations. 
Taking Z and M antilogarithms in AB-36-Z 
and AB-ll-Z, and estimating zooplankton in 
the upper 140 m as before, the following ratios 
(carnivorous micronekton/ zooplankton) are ob- 
tained: 6.0/136.0 = 0.044, and 7.4/191.0 = 
0.039. 
The two copepod/phytoplankton and two 
carnivore/zooplankton ratios, one of each from 
a set of data consistent (or almost so) with 
steady-state conditions and the other not, are 
all about 0.04. Under steady-state conditions, 
ratios between total standing crops at successive 
trophic levels will be approximately the ratios 
between supplies of food available to the suc- 
cessive levels— i.e., "food-chain efficiency ratios,” 
which are expected to be between 0.06 and 
0.15 ( Slobodkin, I960). It is therefore empha- 
sized for the copepod/phytoplankton ratios that 
the numerators, if considered to represent all 
herbivores, are too low. Similarly for the carni- 
vore/zooplankton ratios, the numerators, if con- 
sidered to represent all primary carnivores, are 
too low; the denominators, if considered as 
herbivores, are too high; and the denominators 
probably include more interstitial water, pro- 
portionate to their size, than the numerators. 
Thus the ratios given above are probably all too 
low, if considered as ratios between total crops 
at successive trophic levels, and need not be con- 
sidered deviant from the range of expected 
values given above. 
It is not very meaningful to make compari- 
sons between estimates of standing crop of phy- 
