Standing Crops and Trophic Levels— Blackburn 
45 
time: the former, being more heterogeneous and 
consisting of smaller animals (many of which 
have numerous appendages), probably retains 
more interstitial water after filtration than does 
the latter. Therefore these three sets of measure- 
ments lack the common biological base that the 
common unit, ml/10 3 m 3 , might suggest. 
Stations 
The standing crop of chlorophyll a was rou- 
tinely measured at stations occupied about local 
noon, so that it might be compared (for other 
purposes) with measurements of primary pro- 
duction and submarine daylight; the latter are 
most conveniently made or started about noon. 
There was seldom enough time to take water 
samples for chlorophyll a at night stations, and 
when this was done the number of sampled 
depths was generally only four. On the other 
hand, the crop of micronekton was generally 
measured at stations occupied about local mid- 
night, because of diurnal vertical migration 
(King and Iversen, 1962); it would have been 
necessary to lower the net to a much greater 
depth to obtain similar samples in the daytime, 
and time did not permit this. These and other 
research requirements of the cruises dictated a 
schedule of two major stations per day, at about 
local noon and midnight, on the cruises listed in 
Table 1. Generally a zooplankton haul was made 
at each of these stations except on Step-I, where 
it was frequently omitted- at the noon station. 
As a result there are no stations at which ac- 
ceptable measurements of all three standing 
crops were made at the same time and place, 
although a few such sets of measurements were 
obtained within <36 hr at the same place (Table 
1, footnote 1). For this study it was decided to 
pair adjacent noon and night stations which 
were separated by <120 miles (see numbered 
lines of varying length, e.g., B1 in Fig. 2) and 
<36 hr. Within these limits, the stations to be 
paired were chosen to (a) maximize the num- 
ber of station-pairs, and (b) minimize differ- 
ences in time, space, and physico-chemical 
conditions within pairs. Five pairs were dis- 
carded because the ratio, night zooplankton/ 
noon zooplankton, exceeded the highest such 
ratio observed at the same place (i.e., 2.4 for 
pair A4 in Table 1); it was thought that such 
high ratios might signify large differences in 
biological conditions between adjacent stations. 
The remaining 81 pairs are listed in Table 1. 
Zooplankton data are not given for TO-59-2 
because haul depth was very variable (the ship 
could not maintain the desired speed ) . For each 
station-pair on the other four cruises, there are 
available for analysis one measurement of stand- 
ing crop of chlorophyll a, one of zooplankton,, 
and one of carnivorous micronekton. The zoo- 
plankton value is the geometric mean of the 
listed noon and night values, except for Step-I, 
where it is the night value. 
Measurements of copepod standing crops are 
given for each noon and night station in Table 
1, parts A and B, in the same way as the crops of 
zooplankton of which they formed part. The 
value used for each station-pair in the statistical 
analysis was the geometric mean of noon and 
night values, corresponding to the similar statis- 
tic for zooplankton. The coefficient of correla- 
tion between the two sets of geometric means 
is +0.881, which is significant at the 1% level 
of probability. 
Table 2 shows only pairs of chlorophyll a and 
zooplankton measurements. Each pair refers to 
a single station which was occupied generally 
about local noon. 
Positions of station-pairs and stations listed in 
Tables 1 and 2 may be found as follows: Table 
1, A — Flolmes and Blackburn (I960), also 
Figure 2 of this paper; Table 1, B — Griffiths 
(MS), also Figure 2 of this paper, also Blackburn 
and associates (1962, Fig. 2); Table 1, C — 
Scripps Institution of Oceanography (1961); 
Table 1, D and E — Blackburn et al. (1962); 
Table 2 — Holmes et al. (1957) for Eastropic, 
Holmes et al. (1958) for Scope, and Scripps 
Institution of Oceanography (I960) for Costa 
Rica Dome. 
STATISTICAL ANALYSIS: RELATIONS 
BETWEEN VARIABLES 
General 
Table 3 gives total and partial correlation co- 
efficients among standing crops for the station- 
pairs of Table 1 and stations of Table 2. Parts 
A and B of Table 1, representing two cruises 
made in the Northern Hemisphere spring, have 
