THE RELATIVE IMPORTANCE OF NANNOPLANKTON AND 

 NETPLANKTON AS PRIMARY PRODUCERS IN THE CALIFORNIA 



CURRENT SYSTEM 



Thomas C. Malone' 



ABSTRACT 



Nannoplankton and netplankton primary productivity and standing crop were measured on a seasonal 

 basis in Monterey Bay (October 1969 to February 1971) and along four transects of the California Cur- 

 rent between lat 35° and 50° N. Nannoplankters accounted for 60 to 99% (mean =: 86%) of the ob- 

 served productivity and standing crop both inshore and offshore under oceanic conditions. Seasonal 

 and geogi-aphical variations in the nannoplankton fraction were remarkably stable, and variations in 

 phytoplankton productivity and standing crop were due primarily to the netplankton. The assimilations 

 ratios of both fractions were relatively constant. 



Increases in the netplankton fraction were closely coupled with the occurrence of coastal upwelling, 

 and netplankton productivity and standing crop e.xceeded that of the nannoplankton only during the 

 strongest upwelling pulses. These increases were probably due to the suspension effect of positive ver- 



tical advection and to increases in ambient NO<,-N concentrations above 1 to 3 



/i" 



Decreases were in 



response to increases in grazing pressure and downward water movements. A model is suggested to ac- 

 count for the following observations: (1) the nannoplankton fraction varied within narrow limits com- 

 pared with the netplankton; (2) nannoplankton assimilation ratios (and presumably growth rates) 

 were consistently high and twice those of the netplankton; and (3) netplankton productivity and stand- 

 ing crop increased relative to the nannoplankton during periods of upwelling. The model is based on the 

 response of particles of varying sinking rates to vertical and horizontal advection, and on the degree of 

 coupling between the production of organic matter by primary producers and grazing by primary con- 

 sumers. 



The phytoplankton can be divided into two size 

 classes based on their retention by fine mesh 

 nets (aperture size 20 to 90 /x) . Those retained 

 are commonly called "netplankton" while those 

 which escape are referred to as "nannoplank- 

 ton." Seasonal and geographic variations in 

 netplankton and nannoplankton primary produc- 

 tivity and standing crop are neither well docu- 

 mented nor understood. Previous investigations 

 in both temperate (Yentsch and Ryther, 1959; 

 McAllister et al., 1959; Gilmartin, 1964; Ander- 

 son, 1965) and tropical marine environments 

 (Steeman Nielsen and Jensen, 1957; Holmes, 

 1958a; Teixeira, 1963; Saijo and Takesue, 1965; 

 Malone, in press a) have demonstrated that the 

 nannoplankton are usually responsible for 80 to 

 100% of the observed phytoplankton productiv- 

 ity and standing crop. Netplankton produc- 



' Department of Biology, The City College, City Uni- 

 versity of New York, New York, N.Y. 10031. 



Manuscript accepted June 1971. 

 FISHERY BULLETIN: VOL. 69, NO. 



tivity is often higher in neritic than in oceanic 

 waters (e.g., Steemai^Nielsen and Jensen, 1957; 

 Malone, in press a) but rarely exceeds that of the 

 nannoplankton. However, neritic phytoplank- 

 ton communities dominated by the netplankton 

 in terms of cell number (Digby, 1953) and chlo- 

 rophyll concentration (Subrahmanyan and Sar- 

 ma, 1965) have been reported. 



The ecological significance of these two size 

 classes lies in the role of cell size and surface 

 area-to-volume (A/V) ratios in the dynamics of 

 phytoplankton productivity and energy flow 

 through pelagic food chains. Small cells gen- 

 erally have shorter generation times and higher 

 growth rates in a given environment than do 

 larger cells (Findenegg, 1965; Williams, 1965; 

 Eppley and Sloan, 1966; Eppley and Thomas, 

 1969; Eppley et al., 1969). Recent observations 

 on the kinetics of nutrient uptake by phytoplank- 

 ton (Eppley et al., 1969) indicate that the half- 

 saturation constants (Ks) for nitrate and ammo- 



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