MALONE: RELATIVE IMPORTANCE OF NANNOPLANKTON AND NETPLANKTON 



transport normal to the coast because of their 

 lower sinking rates, netplankton cells would 

 have a greater tendency to remain closer to the 

 region of upward water movement than nanno- 

 plankton cells (Stommel, 1949). Both of these 

 processes, selective grazing by organisms with 

 short generation times and horizontal advection 

 away from upwelling sites, would limit increases 

 in nannoplankton standing crop during upwell- 

 ing and could compensate for the growth rate 

 differential between the netplankton and nanno- 

 plankton fractions. This would set the stage 

 for netplankton productivity and standing crop 

 to exceed that of the nannoplankton during up- 

 welling, and also explain the discrepancy be- 

 tween nannoplankton growth rates and their 

 response to photic zone enrichment. Decreases 

 in nannoplankton standing crop due to "exces- 

 sive" grazing or removal from the photic zone 

 by downward water movements would be damp- 

 ened by the short generation times (and, there- 

 fore, potentially rapid response time) and mo- 

 tility of the nannoplankton species. 



Comparisons of the Oceanic Period in Mon- 

 terey Bay with the offshore oceanic environment 

 of the California Current reveals an interesting 

 pattern of netplankton and nannoplankton vari- 

 ation which is consistent with the above model. 

 The productivity and standing crop of the net- 

 plankton fraction did not vary significantly 

 between the Oceanic Period inshore and the off- 

 shore oceanic zone. In contrast, the nannoplank- 

 ton were significantly higher inshore than off- 

 shore (Table 5). This "inshore enhancement" 

 effect during intrusions of oceanic water could 

 arise in response to the overall pattern of circu- 

 lation. The vertical distribution of nannoplank- 

 ton chlorophyll compared with that of the net- 



Table 5. — Mean netplankton and nannoplankton produc- 

 tivity and standing crop with 95 7r confidence limits for 

 the Oceanic Period at CalCOFI 3 and the oflFshore oceanic 

 region of the California Current. 



plankton indicated that nannoplankters are more 

 independent of vertical water movements and 

 are better able to maintain their position in the 

 water column. This ability, probably a conse- 

 quence of motility, will result in a concentration 

 of nannoplankton in regions of downward flow 

 (Hutchinson, 1967). In addition, the ability of 

 nannoplankton to maintain their position in the 

 photic zone could give rise to a situation anal- 

 ogous to the "island mass effect" described by 

 Doty and Oguri (1956). The former is more 

 likely, however, since assimilation ratios were 

 equivalent in both inshore and offshore environ- 

 ments, i.e., the increase in primary productivity 

 was a consequence of higher standing crops 

 rather than an increase in growth rates. 



SUMMARY AND CONCLUSIONS 



Phytoplankton productivity and standing crop 

 were low under oceanic conditions, both inshore 

 and offshore. During the Oceanic Period in 

 Monterey Bay the nannoplankton accounted for 

 60 to 99 '"r of the observed productivity and 

 standing crop, while offshore this fraction was 

 responsible for 75 to 99 9r . The productivity and 

 standing crop of the netplankton fraction were 

 exceedingly low and constant under these condi- 

 tions, but the nannoplankton fraction was signi- 

 ficantly higher inshore than offshore. Netplank- 

 ton productivity and standing crop exceeded 

 that of the nannoplankton only during periods of 

 strong upwelling. 



The netplankton fraction was composed al- 

 most exclusively of diatoms while the nanno- 

 plankton fraction was dominated by flagellates. 

 Similar, but more detailed observations off La 

 Jolla, Calif., (Reid et al, 1970) showed the nan- 

 noplankton to be composed primarily of naked 

 dinoflagellates, "monads" (e.g., Chilomonas ma^ 

 rina and Eidreptia sp.), and coccolithophores 

 (e.g., Coccolithis hiixleyi) . 



The nannoplankton fraction was surprisingly 

 stable both seasonally in Monterey Bay and geo- 

 graphically in the California Current system. 

 Variations in phytoplankton productivity and 

 standing crop were due primarily to the net- 

 plankton with the nannoplankton maintaining 

 a comparatively stable background level. 



817 



