Table 6.— Values needed to calculate 95% confidence limits for predicted dry weights 

 (DW) and displacement volumes (DV) from the equations in Tables 3-5. For an explana- 

 tion of symbols and the methods used, one should consult Ricker (1973) or Wiebe et al. 

 (1975). 



slope and elevation from all other seasonal lines 

 and had a high rvalue (Table 2). Since the occur- 

 rence of siphonophores in large numbers has 

 been reported in our sampling areas (Sumner 

 1911; Rogers etal. 1978), this predictive equation 

 should be useful for future occurrences of this 

 phenomenon. 



A coefficient of variation (cv) was calculated 

 for each group of displacement volume and dry 

 weight measures in order to compare the relative 

 variability between the two indexes. As expected, 

 both indexes were highly variable, with cv's 

 averaging 54.3% (31.6-133.5%) and 65.4% (33.4- 

 147.8%) for displacement volume and dry weight, 

 respectively. Surprisingly, of the 36 data sets, 31 

 exhibited higher cv's for dry weight than for dis- 

 placement volume. A two-tailed variance test 

 was used to determine whether this difference 

 was significant (Lewontin 1966) for the paired 

 displacement volume-dry weight values. Only 

 GOM late autumn (1977) displacement volumes 

 had a significantly (P<0.05) lower cv than the 

 corresponding dry weights. When all values 

 were combined, however, and a single cv calcu- 

 lated for each index, displacement volumes were 

 significantly (P<0.05) less variable. This was un- 

 expected, because water retained interstitially 

 and intracellularly should increase variability 

 among displacement volumes. It appears, then, 



that displacement volume is a more consistent 

 and more reliable measure of plankton standing 

 stock than dry weight. 



Zooplankton standing stock for 1977 and 1978 

 in each area is plotted in Figure 3A-C. The mea- 

 sures are juxtaposed in order to reveal whether 

 any discrepancies exist between the two pat- 

 terns. For SNE and GB the two indexes of abun- 

 dance follow strikingly similar patterns. In the 

 GOM, however, the dramatic midautumn in- 

 crease in dry weight for 1977 is not equally re- 

 flected by the displacement volume curve. Cala- 

 nus finmarchicus dominated these samples 

 (Sherman et al. 1978) and further examination 

 revealed that they were stage V copepodites, the 

 condition in which they overwinter. Comita et al. 

 (1966) showed that C. finmarchicus collected 

 from the Bute Channel, England, reach their 

 weight and caloric maxima in autumn and early 

 winter, with stage V individuals having the high- 

 est values. The impact these overwintering pre- 

 adults had on the dry weight measures was 

 confirmed by plotting the seasonal mean dry 

 weight-displacement volume ratios for all three 

 areas (Fig. 4). GOM autumn ratios were highest 

 for both years, 17.4% and 13.4%, respectively. 

 Furthermore, samples dominated by C. fin- 

 marchicus had higher ratios than samples from 

 shallower stations where the copepods Pseudo- 



638 



