FISHERY BULLETIN: VOL. 69, NO. 4 



nium uptake vary in proportion to cell size, pre- 

 sumably a consequence of the high A/V ratios 

 of smaller cells (Munk and Riley, 1952). Some 

 evidence is also available that niaximum uptake 

 rates ( Vm) , while not species specific, do increase 

 with increasing cell size (Dugdale, 1967; Ep- 

 pley et al., 1969) so that netplankters with high 

 Ks and Vm values would be favored when nitrate 

 concentrations are high while nannoplankters 

 with low Ks and V,„ values would be favored 

 when nitrate concentrations are low. 



High A/V ratios facilitate suspension (Munk 

 and Riley, 1952; Smayda and Boleyn, 1966a, 

 b; Eppley et al., 1967) increasing the potential 

 residence times of cells in the photic zone under 

 stratified conditions. Also, since sinking rates 

 generally increase as cell size increases, larger 

 cells will tend to be concentrated in regions of 

 upward water flow while smaller cells will be 

 distributed along a gradient toward regions of 

 downward water flow (Stommel, 1949; Semina, 

 1968). In this way, small cells will tend to be 

 spread over a greater volume than larger cells, 

 and motile cells seeking to maintain their po- 

 sition in the water column will be concentrated 

 in regions of downward flow (Hutchinson, 

 1967). 



In addition, the distribution of productivity 

 and biomass among diff'erent size classes of phy- 

 toplankton should be reflected in the distribu- 

 tions and abundances of herbivores which 

 selectively graze on the basis of particle size. 

 Nannoplankters appear to be the preferred food 

 of many planktotrophic larvae (Bruce et al., 

 1940; Thorson, 1950) and microzooplankton 

 (Beers and Stewart, 1969; Parsons and Le Bras- 

 seur, 1970), while herbivorous copepods actively 

 select netplankton species (Harvey, 1937; Mul- 

 lin, 1963; Conover, 1966; Mullin and Brooks, 

 1967; Richman and Rogers, 1969). Phytoplank- 

 ton cell size may also aflfect the efliciency of ener- 

 gy transfer to large predators, since nannoplank- 

 ton-based food chains appear to require one or 

 two additional energy transfers to reach a given 

 sized consumer than do netplankton-based food 

 chains (Ryther, 1969; Parsons and Le Brasseur, 

 1970). 



The California Current system and Monterey 

 Bay provide ideal environments in which to 



study variations in netplankton and nannoplank- 

 ton productivity and standing crop, since nu- 

 trient concentrations and vertical water move- 

 ments vary markedly both seasonally and geo- 

 graphically. The California Current system is 

 discussed by Reid et al. (1958) , and the monthly 

 mean charts of geostrophic flow have been pre- 

 pared by Wyllie (1966). The southerly flow of 

 the California Current is typically strongest 

 during the spring and summer when northerly 

 winds are best developed. At this time the 

 coastal boundary of the Current is marked by 

 upwelling. During the fall and winter northerly 

 winds are weak or reversed, and a coastal coun- 

 tercurrent (the Davidson Current) often devel- 

 ops between the California Current proper and 

 the coast. Thus, the hydrography of the coastal 

 region off' California is generally characterized 

 by upward water movements and high nutrient 

 concentrations during the spring and summer, 

 and downward water movements and low nutri- 

 ent concentrations during the fall and winter. 

 The annual cycle of hydrographic conditions 

 in Monterey Bay has been described by Bolin 

 and Abbott (1961) and Bolin (1964). Skogs- 

 berg (1936) divided the annual cycle in the up- 

 per 100 m into three hydrographic periods: 



1. An Upwelling Period (March to Septem- 

 ber) characterized by low surface temper- 

 atures (9.5° to 11.5° C), high salinities 

 (33.2 to 33.9;^f), and high nutrient concen- 

 trations (>2.0 fxM POj-P, >5.0 /iM NOs-N, 

 and >10.0 fiU SiO^-Si). 



2. An Oceanic Period (September to Novem- 

 ber) characterized by high surface temper- 

 atures (12.0° to 15.0° C), decreasing salin- 

 ities (33.0 to 33.6',',) and low nutrient 

 concentrations (0.2 to 2.0 jjlm PO^-P, 0.0 to 

 0.5 fiM NOs-N, and 1.0 to 10.0 /liM SiO.,-Si). 



3. The Davidson Current Period (November 

 to March) characterized by decreasing tem- 

 peratures (11.0° to 13.5° C), low salinities 

 (32.4 to 33.2:^,), and low nutrient condi- 

 tions. 



Water of oceanic origin is brought into the Bay 

 during both Oceanic and Davidson Current Pe- 

 riods, at first passively as the high density up- 

 welled water begins to subside and then actively 



800 



