GARRISON: NET PLANKTON AND NANNOPLANKTON IN MONTEREY BAY 



NO3 xig atoms lifer'' 

 NHj IO-'>ug atoms liter"' 



10 20 



r- 



-c 50 



a 

 <i> 



Q 



100 



Figure 9. — Vertical distribution of phytoplankton standing 

 stocks, phaeophytin, and hydrographic parameters during 

 upwelling period. Station was sampled during an ebbing tide. 



NOj iug atoms liter'' 

 NH3 IO''4Jg atoms liter'' 



jz 50 



Q. 

 (U 

 Q 



100- 



STATION 8 

 18 JUL. 72 



25.00 



26.00 



Figure 10. — Vertical distribution of phytoplankton standing 

 stocks, phaeophytin, and hydrographic parameters during 

 the oceanic period. 



maximum remains associated with the sinking 

 pycnocline and, although nutrients do not reach 

 limiting concentrations in the pycnocline, light 

 levels are below optimal intensity for maximum 

 growth rates (Figure 10). 



Broenkow and McKain (1972) demonstrated 

 that tidal effects have a marked influence on the 

 distribution of hydrographic parameters over the 

 canyon: during a flow tide there is a down-canyon 

 current and isotherms and isopleths over the 

 canyon are depressed; conversely, during an ebb 



tide the flow is up the canyon and isotherms and 

 isopleths are nearer the surface. The source wa- 

 ters for the down-canyon flow are subsurface wa- 

 ters from the shallow areas adjacent to the can- 

 yon. These tidal effects can be identified in the 

 distribution of the phytoplankton stocks (Silver 

 and Hansen 1971b), but their importance is un- 

 known. The chlorophyll a maximum at station 8 

 (in Figure 8) appears to be an intrusion of stocks 

 developed in shallower areas and carried to depth 

 by the down canyon flow during the flow tide. 

 Station 3 was sampled earlier during an ebb tide, 

 and the sigma-t surface at 50 m (crt = 26.14) was 

 found deeper than 100 m at station 8 (see Figure 

 8). At a full ebb tide the pycnocline and the stand- 

 ing stocks may be located very near the surface 

 (Figure 9). 



DISCUSSION 



The net plankton-dominated blooms that de- 

 veloped during this study were similar to those 

 described by Bolin and Abbott (1963) and Abbott 

 and Albee (1967) in their close association with 

 seasonal upwelling and in their composition (i.e., 

 the net plankton was dominated by colonial 

 diatoms — M. Silver unpubl. data^). Malone 

 (1971c) noted an increase in net plankton fraction 

 during the upwelling season; however, he re- 

 ported net plankton dominated stocks only dur- 

 ing strong upwelling pulses. Malone also reported 

 a marked decrease in net plankton chlorophyll 

 and productivity between inshore and offshore 

 stations near the end of the upwelling season. Al- 

 though these studies cannot be directly com- 

 pared, they suggest phytoplankton blooms which 

 develop during upwelling are mostly net plank- 

 ton forms, and higher standing stocks may develop 

 inshore. 



There seems to be a fundamental contradiction 

 in the measured growth rates of the two fractions 

 and the observed standing stocks. The growth 

 rates of the nannoplankton were consistently 

 higher than those of the net plankton, whereas 

 the standing stocks of nannoplankton decrease 

 and the stocks of net plankton increase during 

 the upwelling season. The observed development 

 of the stocks could result theoretically from one 

 or a combination of the following conditions: 1) 



^The unpublished data supplied by M. Silver can be found in a 

 data report filed in 1971-72 at Oceanographic Services, Inc., 135 

 East Ortega Street, Santa Barbara, CA 93101. 



189 



