MALONE: RELATIVE IMPORTANCE OF NANNOPLANKTON AND NETPLANKTON 



Phytoplankton assimilation ratios (mgC hr~' 

 mgChl-a"') were relatively constant, with most 

 values falling between 5 and 10 (mean =r 7.4 

 ± 1.0, 95'^'e confidence limits). Fluctuations in 

 the amount of chlorophyll-a per cell (10~^ fig) 

 were also within comparatively narrow limits. 

 Values varied from 0.85 to 6.97 with a mean of 

 2.62 ± 0.66. 



Surface levels of nannoplankton productivity 

 and standing crop were remarkably stable 

 through the year. Productivity and standing 

 crop values were less than 8.0 mgC m~^ hr^S 

 0.80 mgChl-a m-^ and 3.3 x 10= cells/liter dur- 

 ing the Oceanic Period. During the Upwelling 

 Period productivity ranged from 6.6 to 18.6, 

 chlorophyll-a from 0.46 to 2.44, and cell numbers 

 from 5.1 to 14.4 X 10^ Thus, while nanno- 

 plankton productivity and standing crop were 

 lower under oceanic than upwelling conditions, 

 the diflferences were not marked. 



In contrast, netplankton productivity and 

 standing crop varied tremendously during the 

 year, from less than 0.6 mgC m"^ hr~*, 0.14 

 mgChl-a m~', and 0.1 X 10= cells/liter during 

 the Oceanic Period to greater than 2.8, 0.40, and 

 0.6 X 10= during the Upwelling Period. Two 

 prominent peaks were observed (31.8 mgC m~^ 

 hr-', 6.76 mgChl-a m-^ and 36.8 and 9.83), both 

 in association with the two most intense upwell- 

 ing pulses. A secondary peak occurred in mid- 

 June. Netplankton cell numbers reached suc- 

 cessive peaks of 24.2, 27.1, and 23.8 x 10= cells/ 

 liter which coincided with peaks in productivity 

 and chlorophyll-a. During the fall and early 

 winter Mixed Period, intermediate values were 

 observed with small peaks associated with each 

 short burst of upwelling. Thus, netplankton 

 productivity and standing crop varied from an 

 order of magnitude less than that of the nan- 

 noplankton during the Oceanic Period to an 

 order of magnitude greater during the Upwell- 

 ing Period. Comparison of mean squares and 

 ranges of variation (Table 2) clearly demon- 

 strates that temporal variations in phytoplank- 

 ton productivity and standing crop were pri- 

 marily due to the netplankton fraction with the 

 nannoplankton maintaining a relatively stable 

 background level. 



Variations in the ratio of netplankton-to-nan- 



noplankton (net/nanno) are also shown in Fig- 

 ure 4. The net/nanno productivity ratio never 

 exceeded 0.3 during intrusions of oceanic water 

 (either during the Oceanic Period or the Mixed 

 Period), and was greater than 1.0 on only two 

 occasions: during the strong upwelling pulses 

 of late March and late January. The same pat- 

 tern was found for the net/nanno chlorophyll 

 and cell number ratios except the chlorophyll 

 ratios were consistently higher and the cell num- 

 ber ratios lower than the productivity ratios. 

 This is reflected in the assimilation ratios and 

 cell chlorophyll-a content of the two fractions, 

 both of which were relatively constant during 

 the study. The mean nannoplankton assimila- 

 tion ratio of 9.4 ± 1.5 was significantly higher 

 than the netplankton mean of 4.7 ± 1.3. Simi- 

 larly, the nannoplankton had more cells per unit 

 chlorophyll-a than did the netplankton. The 

 mean chlorophyll-a content per netplankton cell 

 was 23.6 ± 13.1 x 10" Vs which is significantly 

 higher than the nannoplankton mean of 1.9 ± 

 0.5 X 10 -« ng. 



Peaks in the ratio of netplankton-to-nanno- 

 plankton cell numbers coincided with peaks in 

 netplankton cell number, but the ratio exceeded 

 1.0 only during the January bloom. This prob- 

 ably reflects the dominance of the small-celled 

 (<20 fjL in length), chain-forming diatoms 

 Chaetoceros socialis and Skeletonema costatum 

 in the netplankton fraction. In contrast, the net- 

 plankton blooms of late March and mid-June 

 were dominated by large-celled (>40 fi in 

 length) chain-forming diatoms Nitzschia pacif- 

 ica and Rhizosolenia fragilissima, respectively. 

 Nitzschia spp., Skeletonema costatum, Leptocyl- 

 indricus sp., and Chaetoceros spp. accounted for 



Table 2. — Mean squares and range factors (maximum/ 

 minimum) for nannoplankton and netplankton produc- 

 tivity (PP = mgC m-3 hr-'), chlorophyll-a concentra- 

 tion (mg m~3, m~2)_ and cell numbers (no./liter) at 

 CalCOFI station 3. 



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