FISHERY BULLETIN: VOL. 69, NO. 4 



70% of the netplankton in the March bloom. In 

 mid-June Rhizosolenia spp. and Nitzschia spp. 

 made up 809 of the netplankton. The nanno- 

 plankton fraction was dominated by small mo- 

 nads 2 to 15 jLt in length in all but one of the 

 samples examined. The one exception occurred 

 at the peak of the March-April netplankton 

 bloom when small diatoms dominated the nan- 

 noplankton fraction. When the net/nanno ratio 

 was high (during upwelling), diatoms were 

 more numerous than dinoflagellates; but when 

 the ratio was low (during oceanic conditions), 

 dinoflagellates were more numerous (Figure 

 4c). 



VERTICAL DISTRIBUTION OF PIGMENTS 



The chlorophyll-a content of the water column 

 (0 to 100 m) varied between 14 and 30 mg m"- 

 during the Oceanic Period and between 24 and 

 152 mg m~2 during the Upwelling Period (Fig- 

 ure 5). The seasonal pattern of variation was 

 much the same as that observed for surface 



chlorophyll concentrations, but the range of var- 

 iations was less. 



Variations in netplankton and nannoplankton 

 chlorophyll content of the water column were 

 also similar to the surface pattern. Nanno- 

 plankton chlorophyll-a values fluctuated between 

 the low of 9.6 mg m~^ observed during the 

 Oceanic Period and the high of 44.2 observed 

 during the Mixed Period. Water column levels 

 of netplankton chlorophyll-a, however, were less 

 than 8.0 during the Oceanic Period and sur- 

 passed 110 during both strong upwelling pulses. 

 Again, changes in the phytoplankton chlorophyll 

 content of the water column and in the net/nan- 

 no ratio were due primarily to variations in the 

 netplankton fraction with the nannoplankton 

 fraction remaining comparatively constant 

 (Table 2). 



The vertical distribution of chlorophyll-a al- 

 ways exhibited a maximum which was in the 

 photic zone above or in association with the 

 phaeopigment maximum. The netplankton max- 

 imum was always located below the nannoplank- 

 ton maximum except during strong upwelling 

 when both maxima occurred in the upper 10 m 

 of the photic zone (Figure 6). Four stations 

 have been selected to illustrate the different types 

 of vertical pigment distributions encountered 

 (Figure 7). Two basic patterns were observed, 

 a stable oceanic distribution with low chlorophyll 

 concentrations and low net/nanno ratios (Fig- 

 ure 7a) , and an upwelling distribution with high 

 chlorophyll concentrations and high net/nanno 

 ratios (Figure 7b). Under oceanic conditions, 

 the nannoplankton maximum was found in the 

 upper half of the photic zone, near the bottom of 

 the mixed layer and in nitrate-poor water 



O N D J F 



Figure 5. — Temporal variations in netplankton ( B ) and 

 nannoplankton ( Q ) chlorophyll-a content of the water 

 column (mg m-~, to 100 m) and the net/nanno ratio 

 ( G ) at CalCOFI 3. 



Figure 6. — Temporal variations in the depths of the 

 nannoplankton { "^ ) and netplankton ( A ) chlorophyll-a 

 maxima at CalCOFI 3. 



806 



