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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



that our results are most properly expressed 

 in terms of organisms per cubic meter in the upper 

 200 meters of water. If an estimate is desired 

 of the areal abundance, i. e., the quantity of zoo- 

 plankton in a column of water 200 meters in 

 height and 1 meter square in cross section, it may 

 be obtained by multiplying by 200 the numbers and 

 volumes of zooplankton per cubic meter given in 

 tables 1, 2, 3, and 4. 



COMPOSITION OF THE ZOOPLANKTON 



Tables 5, 6, 7, and 8 show for each cruise and 

 station the percentage composition by number of 

 the 6 major constituents of the zooplankton. It 

 is evident that copepods — by number — were con- 

 sistently the most important constituent. The 

 chaetognaths usually were second in rank, fol- 

 lowed by the tunicates, euphausiids, siphon- 

 ophores, and foraminifers. At several stations 

 other groups, such as radiolarians, annelids, am- 

 phipods, ostracods, and pteropods occurred in 

 considerable numbers, but on the average these 

 animals formed a very small percentage of the 

 collections. As might be expected, the results 

 vary to some extent from station to station; but 

 when the data are summarized, as in table 9, there 

 is revealed a marked and surprising uniformity in 

 composition for the different longitudes and 

 cruises. The percentages given are computed 

 from the sums of estimated numbers for all sta- 

 tions. Percentages by volume for the separate 

 groups were not determined. 



The 210 samples include only a few instances of 

 swarming: Collections taken at stations 7 and 

 9, cruise 5, contained unusually high percentages 

 (60 and 58 percent) of foraminifers; the collec- 

 tion made at station 2, cruise 7, contained a high 

 and unusual percentage (51 percent) of hyperid 

 amphipods. In each case there was no marked 

 change in number for the other major constituents. 



As all of our plankton stations were located 

 in the open ocean with very few within 100 miles 

 of land, the collections consisted primarily of 

 such forms as are permanently planktonic through- 

 out their lives (holoplankton), and contained very 

 few transitory young and larval stages (mero- 

 plankton) of bottom-dwelling forms such as 

 echinoderms, crabs, and clams. 



Table 5. — Cruise 2: Percentage, by number, of six major 

 constituents of zooplankton collections 



[Values less than 1 percent omitted] 



Table 6. — Cruise 5: Percentage, by number, of six major 

 constituents of zooplankton collections 



[Values less than 1 percent omitted] 



