Table 4.- — Average abundance (No. /1, 000 m.') of various plankters from samples taken at night al the IGY station 



Plankters 



Period and (in parentheses) number of samples 



June, 

 July 1957 



(2) 



Aug. 1967 

 (1) 



Sept., Dec. 1957, 

 Oct., Jan., 



Nov. 1957 Feb., 

 Mar. 1958 

 (3) (4) 



Apr. 1958 



(1) 



Aug., 



June, Sept., 



July 1958 Oct., 



Nov. 1958 

 (2) (4) 



CD 



Eight- 

 period 

 mean 



(8) 



Halosphaera' ---- ---- 6,392 



Foraminifera - 660 



Kadiolaria - 204 



Siphonophora.. --- 2, 196 



Chaetognatha 1,346 



Annelida, .-- 184 



Calanoid Copcpoda 12,762 



Non-calanoid Copepoda... 1,369 



Ostracoda - 1,974 



Euphausiacea 1,338 



Amphipoda 958 



Decapod Crustacea - 2,120 



Pteropoda._ 486 



Heteropoda 247 



Gastropod larvae - - 60 



Pelecypoda 60 



Thaliacea 11 



Appendicularia - 135 



Fish larvae -- 234 



Fish eggs - - 96 



' Halosphaera viridit, a phytoplankter. 



1,771 



651 



394 



3,643 



2,834 



157 



38, 733 



2,362 



2,659 



2,440 



905 



3,976 



946 



79 



197 



167 



167 



236 



79 



3,047 



283 



158 



6,943 



2,955 



238 



32,069 



2,301 



2,633 



4,541 



626 



4,460 



1,361 



394 



174 



74 



202 



851 



269 



31 



3,569 



286 



156 



3,055 



1,259 



188 



18,704 



1,192 



3,616 



1,673 



401 



1,842 



546 



38 



33 



177 . 

 464 

 720 

 292 

 90 



6,284 

 1,308 



366 

 4,185 

 4,813 



366 



30, 395 



4,028 



6,069 



3,139 



942 



3,768 



1,360 



62 



105 



1,308 

 3,191 



1,582 



94 



38 



6,137 



2,420 



357 



20, 078 



1,796 



607 



1,662 



869 



3,060 



446 



68 



138 



44 



668 



216 



692 



25 



2,400 

 274 

 142 



3,723 



2,346 



128 



13, 489 



1,898 

 650 



1,893 

 648 



3,331 



1,049 

 118 

 136 

 132 

 146 

 256 

 171 

 21 



6,102 



569 



298 



4,358 



3,128 



410 



24, 916 



2,905 



1,937 



1,788 



521 



5,028 



1,378 



298 



223 



372 



1,639 



112 



3,618 



502 



220 



4,142 



2,638 



254 



23,893 



2,230 



2,480 



2,309 



709 



3,448 



946 



124 



141 



88 



416 



896 



282 



96 



The physical, chemical, and biologioal character- 

 istics of each of the nine periods are discussed be- 

 low. For the discussion the averages for each 

 period are considered liigh or low relative to the 

 overall average for the nine jjeriods. A night sam- 

 ple of zooplankton was not taken in May 1958; 

 thus, the counts of zooplankton for night collec- 

 tions are divided into eight rather than nine 

 periods (table 4). 



JUNE TO JULY 1957 



This period was characterized by relatively high 

 temperatures, low salinities, and a shallow isother- 

 mal layer. The average to 60 m. temperature was 

 25.6° C. The to 60 m. and 200 to 300 m. average 

 salinities were 34.92%o and 35.00%o, respectively, 

 compared to the nine-period means of 34.97%o and 

 35.08%o. The average depth to the top of the ther- 

 mocline was 51.4 m. (fig. 8). 



The average volume of zooplankton for day 

 hauls equaled tlie nine-iieriod mean of 20 cc./ 

 1,000 m.^ (fig. 9) ; the average night volume of 25 

 cc./l,000 m.^ was lower, however, than the eight- 

 period mean of 37 cc./l,000 m.^ Most of the counts 

 of groups of organisms were low (table 4) ; Halo- 

 sphaera, Foraminifera, Amphipoda, and Heter- 

 opoda were exceptions. The abundance of calanoid 

 Copepoda, which numerically make up about 59 

 percent of the total standing crop of zooplankton, 

 was very low during this period. 



AUGUST 1957 



August 1957 appeared to be a transition period 

 (fig. 7). The to 60 m. salinity increased from 

 34.92%o to 34.98%o, and the 200 to 300 m. salinity 

 increased slightly from 35.00%o to 35.02%o. The 

 to 60 m. temperature (26.0° C.) also increased. 

 The depth of the isothermal layer (49.1 m.) de- 

 creased from the previous period. 



The volume of zooplankton for the day hauls 

 (18 cc./l,000 m.^) for this period was slightly less 

 than the average for June to July 1957 ; however, 

 the night volume (44 cc./l,000 m.^) showed a sub- 

 stantial increase. Kadiolaria and calanoid Copep- 

 oda were more abundant in August 1957 than in 

 any other period. 



SEPTEMBER TO NOVEMBER 1957 



Temperature and depth of the isothermal layer 

 for this period were lower; salinities were higher 

 than in the previous period. The average to 60 

 m. temperature was 25.9° C. The depth to the top 

 of the thermocline was 47.4 m. The to 60 and 200 

 to 300 m. salinities were 35.14%o and 35.11%o, 

 respectively. 



The average volumes and counts of zooplankton 

 were high. Volumes for day (25 ce./l,000 m.^) and 

 night (56 cc./l,000 m.') samples were both higher 

 than the corresponding averages (20 cc./l,000 m.^ 

 and 37 cc./l,000 m.^) for all periods. Euphausiacea 

 and Heteropoda were more abundant in this period 

 than in ai>y other. 



VARIATIONiS IN MARINE ZOOPLANKfTON IN HAWAIIAN WATERS 



95 



379-242 O - 70  



