I 



s 

 o 

 o 

 o 



,400 

 ,100 



,800 

 ,500 

 ,200 



900 



600 



300 





 800r 



700- 



600- 



500- 



400 



300- 



HI 



iii.--i..lii 



2001 



100 I 



oU 



0600 1200 



HOUR OF DAY 



HOUR OF DAY 



0600 1200 



HOUR OF DAY 



Figure 9. --Average number of amphipods, pteropods, and fish larvae per 1,000 m.^ of water 

 strained by the three nets on HMS-32 and 34. 



Phytoplankton Bloom 



An occurrence of unusually dense phytoplank- 

 ton was encountered on August 1-6, 1956 (HMS- 

 35). It was so abundant at certain stations that 

 it clogged the coarse-meshed nets. Thorough 

 washing was required after each tow, before the 

 nets could be re-used. 



The principal phytoplankter in the samples 

 was a diatom, Rhizosolenia sp. As a rough 

 measure of abundance, its percentage contribu- 

 tion to the sample volume was estimated (fig. 13). 



MONITOR SERIES 



The monitor series provided information on 

 monthly fluctuations and on differences in abun- 

 dance of zooplankton between windward and lee- 

 ward areas off Oahu. Cruises and dates are 



given in table 1; the station locations are shown 

 in figure 14. The six stations were sampled by 

 making oblique hauls with a single open net at 

 to 60 m. Some of the data for this series were 

 obtained from the comprehensive series. 



Monthly Variations 



Average adjusted volumes and standard devi- 

 ations for collections of zooplankton in the mon- 

 itor series are shown in figure 15. The lower 

 panel, which includes data from both the wind- 

 ward and leeward stations, shows three peaks: 

 a winter peak, probably in January; a spring 

 peak in April; and a fall peak in September. 

 Only the September peak is strongly defined, 

 although the standard deviation is large. This 

 variation is in contrast to the monthly average 

 volumes computed by King and Hida (1957), 



14 



