GARRISON: NET PLANKTON AND NANNOPLANKTON IN MONTEREY BAY 



MONTEREY 

 BAY 



37* N 



Vf 



40' 



36'3r 



Figure l. — Location of stations in Monterey Bay. Broken 

 lines indicate the position of the 100-fathom (183-m) contour 

 line. 



samples were incubated immediately after collec- 

 tion for 3 to 4 h in a shipboard incubator (Doty 

 and Oguri 1958) using Luxor Magnalux fluores- 

 cent lamps^ (approx. 0.06 langley min"^). Neutral 

 density filters of 50, 25, 10, and 1% transmittance 

 were used on subsurface samples. 



The net plankton and nannoplankton fractions 

 were separated by passing the samples through a 

 22-/xm Nitex-net filter (net plankton) and then a 

 Gelman, type A glass-fiber filter having 0.3-/>tm 

 pore size (nannoplankton). Both filters were 

 washed with approximately 20 ml of freshly 

 filtered seawater and placed directly in scintilla- 

 tion fluor for counting at a later time. 



All samples were counted for at least 10 min 

 with a Nuclear Chicago (Unilux II) scintillation 

 counter. Carbon uptake was calculated as out- 

 lined in Strickland and Parsons (1968). Since 

 Malone (1971b) reported no diurnal periodicity in 

 assimilation ratios in the California Current re- 

 gions, daily production was estimated by using 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



the sunrise to sunset interval as the day length 

 and multiplying by the hourly production rates 

 that were determined during the first part of the 

 day. 



Phytoplankton standing stocks were measured 

 as chlorophyll a by using the fluorometric method 

 of Holm-Hansen et al. (1965). The Turner fluoro- 

 meter (model 111) was calibrated using the spectro- 

 photometric method for chlorophyll a as outlined 

 by Strickland and Parsons (1968). The two size 

 fractions were separated by taking two replicate 

 samples from each depth and passing one 

 through a Gelman glass-fiber filter (total chloro- 

 phyll) while the other sample was filtered through 

 22 ;um Nitex-net filter and then a glass-fiber filter 

 (nannoplankton). Both filters were immediately 

 frozen, stored in the dark, and analyzed within a 

 month after collection. Net plankton was calcu- 

 lated as the difference between total chlorophyll 

 and nannoplankton chlorophyll. 



Productivity and chlorophyll a values deter- 

 mined for the discrete samples were integrated to 

 the depth of the 1% light level by trapezoidal ap- 

 proximation. Carbonxhlorophyll a ratios vary 

 widely and depend on light and nutrient condi- 

 tions. For most of the study, nutrient levels were 

 high and a C:Chl a ratio of 40 was used to convert 

 chlorophyll a to carbon biomass (Lorenzen 1968; 

 Eppley et al. 1970; Eppley et al. 1971). Phyto- 

 plankton growth rate and standing stock dou- 

 bling time were calculated using exponen- 

 tial growth expression. 



RESULTS 



In January, the weak thermal gradient in the 

 upper 50 m (Figure 2) is indicative of the David- 

 son Current period, when the subsurface counter- 

 current extends to the surface and flows north- 

 westward on the inshore side of the California 

 Current (Reid et al. 1958; Bolin and Abbott 1963; 

 Smethie 1973). Rising isotherms and nitrate iso- 

 pleths from February through May indicate up- 

 welling over the Monterey Submarine Canyon. 

 After May there was a slacking or an end to up- 

 welling, and the isotherms and isopleths are 

 found progressively deeper as denser upwelling 

 waters subside. In July and August, conditions of 

 the oceanic period were evident with low nutrient 

 levels, higher surface temperatures, and lower 

 salinities; however, upward movement of the 

 isotherms and isopleths in August may indicate a 

 developing upwelling pulse. 



185 



