COLEBROOK II UCTUATIONS IN BIOMASS OF ZOOPLANK I < >X 



that these patterns are reflected generally in the 

 distribution of the plankton of the Pacific Ocean. 

 It may, nevertheless, he significant that the 

 pattern of distribution of the taxonomic categories 

 reflects both the alongshore and the inshore- 

 offshore transitions in the distribution of the 

 Euphausiacea. 



YEAR-TO-YEAR FLUCTUATIONS 

 IN BIOMASS 



Annual means of biomass were calculated, as 

 described above, for each taxonomic category 

 (Table 1) for each of the well-sampled standard 

 zones ( Figure 1 ) for each of the years 1955-59. Two 

 sets of principal components analyses were 

 carried out, firstly for each of the 14 standard 



TABLE 3. — For each zone (a ) the percentage 

 ity of the original data accounted for by the 

 i b ) the number of taxa with positive first 

 imum = 17). The code names for the zones 

 Figures 6 and 9 are also given. 



of the total variabil- 

 first component and 

 vector values (max- 

 used in Table 4 and 



zones on the annual fluctuations in biomass of 

 each taxonomic category and secondly for each 

 taxonomic category on the annual fluctuations in 

 abundance in each of the standard zones. The 

 same data are involved in both sets of analyses. 



Graphs of the first principal components for 

 each of the zone analyses are given in Figure 5. 

 Table 3 shows that these components accounted 

 for between just under one-half and about three- 

 quarters of the total variability; it also shows that 

 all but a very few of the categories showed positive 

 relationships with the components. The graphs 

 show considerable similarity between the various 

 zones. These results indicate that a large element 

 of the year-to-year fluctuation in biomass is 

 common to all the zones and to a vast majority of 

 the taxonomic categories. Nearly all the zones 

 show a relatively high biomass (relative to a mean 

 of zero) in 1955 and 1956 and a low biomass in 

 1958 and 1959. The data for 1957 vary from zone 

 to zone, perhaps tending to be higher in the 

 northern and offshore zones and lower in some of 

 the southern and inshore zones. 



A table was prepared of the corresponding 

 vectors with the taxonomic categories arranged, 

 by trial and error, to give the high positive terms 

 at the top, and the low positive and the few 

 negative terms at the bottom of the table. The 

 final ranking of categories and the vector values 

 are given in Table 4. This rank was compared with 

 the rank of taxa based on the relationships 

 between their geographical distributions (Figure 

 2) starting with the northern distributions, with 

 Siphonophora and Thaliacea, working round the 

 sequence and ignoring Medusae (also left out of 

 Table 4) to finish with Pteropoda and Ostracoda. 



TABLE 4. — The first vectors of principal component analyses for each standard zone with the taxonomic categories ranked as described 



in the text. Also the rank of the categories derived from Figure 2. 



361 



