pteropods were consistently more abundant on 

 the leeward side, and the siphonophores and 

 thaliaceans on the windward side (table 15). 



The season of maximum abundance differed 

 widely among taxa and varied also according to 

 water stratum (tables 9 and 10). In the upper 

 layer the seasons of peak abundance for various 

 taxa were: spring--ostracods and fish eggs; 

 summer — foraminifers, radiolarians, siphono- 

 phores, chaetognaths, euphausiids, decapod 

 crustaceans, pteropods, and fish larvae; and 

 winter--polychaetes. copepods, amphipods, gas- 

 tropod larvae, pelecypods, thaliaceans, appen- 

 dicularians, and Halosphaera . In the middle 

 layer the seasons of peak abundance were: 

 spring--chaetognaths, euphausiids, pteropods, 

 and fish eggs; summer--foraminifers and si- 

 phonophores; and winter--polychaetes, gastro- 

 pod larvae, pelecypods, thaliaceans, and Halo- 

 sphaera . In neither the upper nor the middle 

 layer was any taxon (except for the poorly rep- 

 resented stomatopods) most numerous in the 

 fall. 



The greater abundance of some taxa in sum- 

 mer may have been associated with abundant 

 food in the form of a bloom of diatoms (dis- 

 cussed in a later section). Both the diatom and 

 zooplankton peaks were in the upper layer. 



A substantial increase in Halosphaera oc- 

 curred in the lower stratum during the summer 

 (HMS-35), apparently as the result of a sea- 

 sonal shift in population from the upper two 

 strata (table 11). Whether this shift was relat- 

 ed to light conditions in the summer or to other 

 factors is not known. Unfortunately , no samples 

 were taken from the lower stratum during the 

 fall (HMS-36). 



Total abundance of organisms in the upper 

 stratum was greater on the windward than the 

 leeward side on all four cruises (table 13). 

 This areal difference is attributable to the pre- 

 dominance of decapod crustaceans on the wind- 

 ward side, as mentioned above. Differences 

 between areas were slight in the middle and 

 lower strata (tables 14 and 15). 



Collections during November cruises CHG-24 

 in 1955 and HMS-36 in 1956 provide extremely 

 limited data for a comparison of annual differ- 

 ences in plankton composition. Numbers of 

 most groups of plankters were similar during 

 the 2 years (table 9). Notable exceptions were 

 the radiolarians, ostracods, euphausiids, tha- 

 liaceans, fish eggs, and Halosphaera , whose 

 numbers differed greatly in the 2 years. 



Table 15. --Comparison of average number of organisms per 1,000 m.^ of water strained by 

 the lower net in windward and leeward areas (number of samples shown in parentheses) 



Foraminif era 



Rad iolaria 



Siphonophora 



Chaetognatha 



Polychaeta 



Copepoda 



Os tracoda 



Euphaus iacea 



Amphipoda 



Decapoda (Crustacea) 



Pteropoda 



Heteropoda 



Gastropoda (Larvae) 



Pelecypoda 



Thaliacea 



Appendicular ia 



Fish (Larvae) 



Fish (Eggs) 



Halosphaera 



Total 



6,861 



6,801 



7,462 



10,523 



11,064 



8,692 



12 



