FISHERY BULLETIN: VOL. 74, NO, 1 



ditions are poorly known. Tidal mixing and in- 

 creased turbulence in shallow water could facili- 

 tate cell suspension of sinking populations or 

 resting spores, and increase nutrient input to the 

 surface waters. Over Monterey Canyon and, to a 

 lesser extent, in the shallow areas of the bay, the 

 vertical distribution of nutrients (Broenkow and 

 McKain 1972; Smethie 1973) and phytoplankton 

 stocks (Silver and Hansen 1971b; Silver see foot- 

 note 3) are strongly influenced by tidal effects. 

 Turbulence and mixing in deep water results in a 

 decrease in the average amount of light to which 

 a phytoplankton cell is exposed; however, in shal- 

 low water the depth of mixing is limited by the 

 bottom and mixing here may result in resuspen- 

 sion of sinking cells. Many of the neritic diatoms 

 form resting spores which sink to the bottom and 

 may be an important source of innoculum to ini- 

 tiate blooms if they are resuspended by turbu- 

 lence during favorable growth conditions. 



The decline in the net plankton populations 

 during this study corresponded to the influx of 

 oceanic waters in July. The end of net plankton 

 domination of the population appears to have 

 been the result of the low nutrient concentrations 

 in the oceanic surface waters and subsidence of 

 previously upwelled waters and its entrained net 

 plankton populations. During oceanic conditions, 

 nutrient levels in the surface waters favor the 

 growth of nannoplankton and the light levels in 

 the sinking net plankton maxima are not optimal 

 for growth. Malone (1971c) suggested, however, 

 that the net plankton are ultimately limited by 

 grazers as the grazing index (phaeo:Chl a) in- 

 creased and the netplankton concentrations de- 

 creased even before the end of the upwelling 

 period. Direct evidence for the extent of grazing 

 in Monterey Bay is not available; however, when 

 upwelling becomes sporadic and periodic influxes 

 of oceanic water occur, the stage is set for a de- 

 cline in the net plankton fraction without the 

 need for an increase in grazing pressure. 



ACKNOWLEDGMENTS 



I am grateful for the help of David Seielstad, 

 Sara Tanner, and many others who participated 

 in the sampling cruises. I thank W. W. Broenkow, 

 Scott McKain, and Sandra Benz for providing the 

 hydrographic data. I am particularly indebted to 

 Mary Silver for her encouragement, support, and 

 advice throughout the study and during the prep- 

 aration of this manuscript. Greg Cailliet re- 



viewed the manuscript and offered suggestions 

 for its improvement. 



This research was supported by Grant 2-35137 

 from the office of Sea Grant Programs, National 

 Oceanographic and Atmospheric Administration, 

 Department of Commerce; the Association of 

 Monterey Bay Area Governments; and the Soci- 

 ety of the Sigma Xi and was based on a thesis 

 submitted as a partial requirement for a M.A. 

 degree at San Francisco State University, Calif 



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