FISHERY BULLETIN: VOL. 69, NO. 4 



offshore range of 10.72 to 25.96 mg m-^ (Figure 

 11). In November the pattern was much the 

 same, with an inshore maximum of 66.64 and an 

 offshore level of 23.20. 



Nannoplankton chlorophyll in the water col- 

 umn showed little variability (Figure 11). In- 

 shore levels of nannoplankton chlorophyll varied 

 from 17.49 to 31.94 mg m -, while offshore levels 

 ranged between 9.63 and 21.76. The netplank- 

 ton fraction underwent much greater fluctua- 

 tions (Figure 11). Inshore concentrations 

 ranged between 3.26 and 185.74 in contrast to 

 the offshore range of 1.00 to 4.97. The latter 

 range is equivalent to that observed at Cal- 

 COFI 3 during the Oceanic Period and the for- 

 mer to that observed during the Upwelling Peri- 

 od. Excluding inshore stations, the mean chloro- 

 phyll-a concentration of the nannoplankton f rac- 



3 61 63 

 Inshore 



Figure 11. — Inshore-offshore variations in the netplank- 

 ton (  ) and nannoplankton ( □ ) chlorophyll-a content 

 of the water column (mg m~-, to 200 m) during the 

 July-August transects and the November transect 

 (inset). 



tion was 16.55 ± 2.38 which is significantly 

 higher (P — 0.05) than the netplankton mean 

 of 3.08 ± 0.81. 



The vertical distributions of chlorophyll-a and 

 phaeopigments at the offshore stations of the 

 July-August transects were characterized by a 

 subsurface maximum located at the base of the 

 photic zone, in the lower part of the thermocline, 

 and near the upper reaches of the nitrate-rich 

 layer (Figure 12). Netplankton and nanno- 

 plankton chlorophyll maxima were usually locat- 

 ed near each other, but the netplankton maxi- 

 mum was not always deeper than the nanno- 

 plankton maximum. Netplankton chlorophyll 

 was more evenly distributed and concentrations 

 were much lower than in inshore waters (com- 

 pare Figures 7 and 12) . Both maxima gradually 

 decreased in depth shoreward from between 80 

 and 100 m offshore to 10 m or less at the inshore 

 stations paralleling the upward trend of the iso- 

 therms (Figure 8) and nitrate isopleths (Fig- 

 ure 9). 



The pattern was much different during the 

 November transect (1-B). The netplankton 

 maximum was always located below the nanno- 

 plankton maximum, especially at the inshore 

 station where the netplankton maximum was 

 30 m below the nannoplankton maximum (Fig- 

 ure 7d). Both maxima decreased in depth sea- 

 ward to station 5 (Figures 8 and 9) where the 

 vertical distribution conformed to the upwelling 

 distribution (Figure 12), i.e., netplankton and 

 nannoplankton maxima were in the upper 10 m 

 and nitrate concentrations were relatively high 

 throughout most of the photic zone. Farther off- 

 shore the depth of the chlorophyll maxima in- 

 creased once again. This up and down move- 

 ment of the maxima closely i^aralleled the depth 

 variation of the isotherms and nitrate isopleths 

 just as during the July-August transects. 



DISCUSSION 



The constancy of the phytoplankton assimila- 

 tion ratios both inshore (7.4 ± 1.0) and off- 

 shore (7.7 ± 1.1) suggests that nutrients were 

 rarely limiting to primary productivity (Dick- 

 man, 1969) . The mean assimilation ratios found 

 are close to the value of 7.3 reported by Holmes 

 (1958b) in the nutrient-rich waters of the Costa 



812 



