MALONE: RELAT1\E IMPORTANCE OF NANNOPLANKTON AND NETPLANKTON 



90 no laO liO T.mpl^Ct 



mg Chl-am-3 

  40 30 30 10 10 



90 no 130 ISO i.mprcl 

 ^^ 20 30 NOj-NluMl 



110 130 150 T.mp*-^) 



20 30 NO3-N 



DO 130 T.mpnci 



!£L_, 10 NO,-N 



Figure 7. — Vertical profiles of netplankton ( D ) and nannoplankton (□) chlorophyll-a (mg m"^), NO3-N 

 (^m), and temperature (°C) at CalCOFI 3: (a) Oceanic Period (10 March), (b) Upwelling Period (31 March), 

 (c) Upwelling Period with peak grazing pressure (26 July), and (d) Mixed Period during post-upwelling sub- 

 sidence (6 November). 



( <0.5 fjiM NO3-N) ; while the netplankton max- 

 imum was located in the lower half of the photic 

 zone, in the thermocline, and in nitrate-rich 

 water (>5.0 fiU NO3-N). Maximum phaeopig- 

 ment concentrations occurred in association with 

 or just below the netplankton maximum. With 

 the onset of upwellincr, the netjilankton maxi- 

 mum gradually shifted from a depth of 75 m 

 to the surface (Figure 6). Initially, upwelling 

 had a dilution effect which was followed by a 

 rapid increase in the netplankton fraction and 

 later by a slight increase in the nannoplankton 

 fraction (Figure 5). The upwelling distribution 

 observed on March 31 is shown in Figure 7b. 

 Both netplankton and nannoplankton chloro- 

 phyll maxima were at the surface and nitrate 

 concentrations were high (>5.0 (iM NO.-i-N) 

 throughout the photic zone. 



The remaining two examples represent special 

 cases which evolved from an upwelling distribu- 

 tion such as the one just described. Figure 7c 

 shows the distribution observed during late July 

 that developed over the period of steady upwell- 

 ing during which the grazing pressure index 

 increased markedly (Figure 3) . Note that both 

 netplankton and nannoplankton maxima were 

 in the upper 10 m, and NO3-N concentrations 

 were in excess of 5 (jlM throughout the photic 

 zone; but that the concentration of netplankton 

 chlorophyll has been greatly reduced and the 

 net/nanno ratio was low. Phaeopigments were 

 high with a maximum just below the netplankton 

 chlorophyll maximum. The distribution shown 

 in Figure 7d (November 6) developed during 

 a period of subsidence following an upwelling 

 pulse. At this time, the netplankton maximum 



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