SAMPLE NUMBER 

 4 5 6 7 8 9 10 II 



12 13 14 15 16 



3,000 

 2,500 

 2,000 



1,500 



1.000 



500 



400 

 300 

 200 

 100 



OSTRACODA 



HETEROPODA 



0000 0600 1200 1800 0000 

 LOCAL STANDARD TIME 



0600 1200 



Figure 2. — Variation in the abundance of various groups 

 of zooplanliters during June 21-23, 1957, at the IGY 

 station. 



TEMPERATURE 



The diel variation in surface temperature (fig. 

 3) was attributed to solar heating during the day 

 and cooling at night. A subsurface thermal dis- 

 turbance was evident between 0400 and 1200 hours, 

 June 22. It was probably caused by advection; 

 however, unusual changes in the voliunes of 



90 



zoop'ankton did not occur during the thermal 

 disturbance. 



DEPTH FROM SURFACE TO TOP OF 

 THERMOCLINE 



The sinusoidal variation in the depth from the 

 surface to the top of the thermocline (fig. 3) 

 showed fluctuations probably caused by internal 

 waves. The variations in depth to the top of the 

 thermocline, however, did not appear to influence 

 the abundance or composition of the zooplankton 

 during the 4-8-hour period. The depths for the 

 hauls of zooplankton in this series ranged from 52 

 to 65 m. The depth from the surface to the top of 

 the thennocline ranged from 23 to 61 m. Sample 8 

 was the only one collected entirely within the iso- 

 thermal layer above the thennocline. The volume 

 of sample 8 was not unusual. Chaetognatha had 

 their least abundance and Pelecypoda their great- 

 est abundance in this sample. 



CORRELATIONS BETWEEN ZOOPLANK- 

 TON AND PHYSICAL AND CHEMICAL 

 FACTORS 



King and Hida (1954, 1957b), in their studies 

 of the distribution and abundance of zooplankton 

 in Hawaiian waters, were imable to show a con- 

 sistent relation between the standing crop and 

 temperature, surface phosphate, dissolved oxygen, 

 and depth from the surface to the top of the ther- 

 mocline. Analyses of their data from seven cruises 

 gave one statistically significant correlation 

 (P<0.05) Ijetween zooplankton and temperature 

 (at 10-m. depth) and one significant correlation 

 (P <0.01) between zooplankton and surface phos- 

 phate. King and Hida's samples were taken from 

 a large area around the Hawaiian Islands. 



Consistently high or low standing crops regard- 

 less of changes in the environment (McGary 1955 ; 

 Seckel, 1955) have been found in certain areas in 

 Hawaiian waters. For example. King and Hida 

 (1954, 1957b) foimd consistently low volumes of 

 zooplankton from immediately east of the island 

 of Hawaii. 



The results of the correlation analyses for the 

 present study, where sampling was confined to one 

 locality, are summarized in table 2. Volumes of 

 zooplankton were examined in relation to the phys- 

 ical and chemical data for tiie surface, to 60 m. 

 (range in depth of the hauls for zooplankton), 



U.S. FISH AND WILDLIFE SERVICE 



