to 60 m. and 200 to 300 m. salinities (fig. 8), but 

 their temperatures were quite dissimilar (fig 8). 



VARIATIONS OF ZOOPLANKTON AND 

 SALINITY 



Of great interest were the coincident variations 

 in the night volumes of zooplankton with varia- 

 tions in the portions of the T-S curves with salini- 

 ties >35.0%o. As shown in figures 7 and 9, increases 

 or decreases in night volumes of zooplankton ap- 

 peared with corresponding changes in the salinity. 

 The T-S curves indicated a progressive invasion 

 of high-salinity wat«r in the upper surface layers 

 from June to July 1957 to September to November 

 1957. The night volumes of zooplankton increased 

 correspondingly during these same periods. In 

 December 1957 to March 1958, less saline waters 

 returned to the uppermost layer of the ocean and 

 the volume of zooplankton dropped below that of 

 the preceding period. Then in April 1958 high- 

 salinity water again invaded the area, and the 

 volume of zooplankton increased. During May 

 1958 the salinity maximum was about the same as 

 in the previous period, but the surface water was 

 less saline. A night volume of zooplankton was not 

 available for this period. During the next two 

 periods, June to July 1958 and August to Novem- 

 ber 1958, the occurrence of high-salinity waters 

 decreased progressively. Corresponding decreases 

 also were evident in the night volumes of zooplank- 

 ton. Water of higher salinity returned again in the 

 uppermost layer during December 1958 coincident 

 with an increase in the night volume of zooplank- 

 ton. 



Thus, waters of high salinity appeared to sustain 

 a greater biomass of zooplankton. The abundance 

 of several groups of zooplankton fluctuated coinci- 

 dentally with the night volumes and with salinity. 

 These groups were Siphonophora, Chaetog- 

 natha, Euphausiacea, decapod Crustacea, and Pte- 

 ropoda (fig. 10). Because of the correlation of the 

 abundance of these zooplankters with water type, 

 the possibility of finding endemic species appeared 

 favorable. Sherman (1963) found certain species 

 of calanoid Copepoda (Pontellidae) associated 

 with, and thus useful as indicators of, waters of 

 high salinity (North Pacific Central Water) in 

 the Hawaiian area. These groups of zooplankton 



98 



9flOO 



8,000 



7,000 



6,000 



5,000 



4,000 



3,000 



2,000 



1,000 





 5,000 



4,000 



3,000 



2,000 



1,000 





 50,000 



40,000 



2 30,000 



o 

 o 



Q. 20.000 



o 10,000 



UJ 



2 



3 6.000 



§ 



5,000 



4,000 



3.000 



2,000 



1,000 





 7,000 



-EIGHT-PERIOD MEAN 



m 



^ 



m 



m 



"^ 



I 

 i 



2a 



va 



i 



■I 



m 



rti 



i 



6,000- 

 5,000 

 4,000 

 3,000 

 2,000 

 1,000 



'777/ 





 3,000 



Siphonophora 



 



1 



i 





Chaetognotho 



I 



Calanoid Copepoda 



m 



1 



Euphousioceo 



 ■I 



Decapod Crustacea 



P 



i 

 I 



2,000 



1,000 







Pteropoda 



r^ 



JUNE AUG SEPT DEC Al 

 JULY NOV MAR 



1957 1957-1958 



MAY JUNE Ay6. DEC. 

 JU.Y NOV 



1958 



Figure 10. — Average abundance of six groups of zoo- 

 plankton at night during eight periods at the IGY 

 station. 



U.S. FISH AND WILDLIFE SERVICE 



