FISHERY BULLETIN: VOL. 70, NO. 4 



Figure 4. — Urea concentrations at the same 

 depth for paired stations sampled on the 

 same day during Period A, Period B, and 

 Period C, 



0.9 



0.8 



0.7 



^ 0.6 



z 

 I 

 < 



LlJ 



cr 



^•0.5 



o 



en 



3 



H 0.4 

 < 



cn ' 



Z 0.3 



< 



t- 



0.21 



0.1 



D Period A 

 O Period B 

 A Period C 



A O 



AA 



An A ° nA 



y 



D A Q i 



rVA 



0.1 0.2 0.3 0.4 0.5 



STATION n (/jg at. UREA-N/I) 



0.6 



0.7 



Table 2. — Linear regressions of Station I or III vs. 

 Station II for nitrate, nitrite, ammonium, and urea 

 within each period. 



Nutrient 



Period 



Station I or III 

 vs. Station II 



Pi 



Probability that the regression slope is not different from zero. 



are for the two-sided test and since these same 

 data will be used for another analysis the level 

 of significance {a) is taken as 0.05/2, 



Vaccaro and Ryther (1960) observed maxi- 

 mum concentrations of nitrite when both phyto- 

 plankton and nitrate were abundant at light 

 limiting depths. Tau coefficients indicated that 

 in the present study there were no significant 

 correlations between either 1) the median chlo- 

 rophyll a and the median nitrite concentrations 

 below the thermocline (P = 0.288) or 2) the 

 chlorophyll a and the nitrite concentrations at 

 or within 5 m of the thermocline (P = 0.490). 



Lorenzen (1967) suggested that a phaeo-pig- 

 ment/chlorophyll ratio is indicative of herbivore 

 grazing pressure, and since ammonium is the 

 major nitrogenous excretion product of most ma- 

 rine crustaceans (Parry, 1960), we used the tau 

 coefficient to examine the phaeo-pigment/chlo- 

 rophyll ratios and ammonium and urea data from 

 this study for positive correlation. If one as- 

 sumes that the single pigment profile taken each 

 sampling day is representative of the whole area 



1268 



