FISHERY BULLETIN: VOL. 69, NO. I 



rections for respiration by phytoplankton were 

 made. 



Ammonium was measured ashore in frozen 

 samples from a depth of 10 m by the method of 

 Richards and Kletsch (1964). Some labile 

 amino-N which is probably available to phyto- 

 plankton is measured along with ammonium by 

 this method. 



RESULTS AND DISCUSSION 



For the comparison of calculated and mea- 

 sured ^''C production, we have used samples 



from 10 m incubated at light intensities approx- 

 imating those at 10 m to determine Ks and fimax. 

 and actual ^^C values from the 50% light level. 

 We did this so that light intensities would not 

 be a factor in the comparison — that is, light 

 was presumed to be at saturating intensities 

 but not inhibitory, which would be the case if 

 surface samples had been incubated in the 

 growth experiments and compared with surface 

 production. 



Ammonium was not determined at all pro- 

 duction stations, and we selected those pro- 

 duction values where data were available for 



OBSERVED '*C PRODUCTION {Mg C/m'/Day) 



10 



Figure 1. — Phytoplankton production calculated from ammonia and chlorophyll con- 

 centrations at 10 m compared with simulated in situ ^^C production at the 50 7o light 

 level in northerly nutrient-poor water in the eastern tropical Pacific Ocean. The dashed 

 line is the regression that would be expected if agreement between the two sets of pro- 

 duction values were perfect. 



90 



