exposed to increasing concentrations (100, 250, 500, 1,000, and 2,250 

 milligrams 1"-^) of the silicon: dioxide (Si02) particles with a median 

 size approximately 17 micrometers. The other three species were 

 exposed to graded concentrations (50, 100, 500, and 1,000 milligrams 

 1-1) of the Si02 particles with a median size of 6„2 micrometers (see 

 App.). 



A slurry of Si02 particles was made up with filtered, sterile 

 (autoclaved) , enriched (f/2 medium) Patuxent River water before the 

 start of each experiment. A magnetic stirring device was used to main- 

 tain the suspension. Concentration of particles by weight (milligrams 

 1~^) was determined by the dry weight difference between the average of 

 three oven-dried aliquots (5 milliliters each) of the slurry and the 

 average of three aliquots (5 milliliters each) of the enriched river 

 water (salt correction) . 



Fifteen glass-stoppered bottles, rinsed and washed as in the satur- 

 ation curve determinations, were used for each experiment. Of these, 

 five replicate pairs were light bottles. Each of these pairs had a 

 corresponding dark bottle which had been wrapped with two layers of 

 heavy gage aluminum foil. All bottles were filled with cells (approx- 

 imately 50,000 cells ml~l) from the same culture flasks. Small amounts 

 of the Si02 slurry were measured by volume (Oxford precision micropipet) 

 and injected into the bottles (two light and one dark bottle received 

 the same concentration) to make up the series of increasing Si02 con- 

 centrations. The amount of slurry injected never exceeded 0.5 percent 

 of bottle volume (130 milliliters). After approximately 1.0 microcurie 

 NaHC^^Os was injected into each bottle with a gas-tight syringe dark 

 bottles were completely wrapped and all bottles were stoppered. 



The rest of the procedure (incubation and isotope counting) was 

 similar to that of the saturation curve determinations with these 

 exceptions : 



(1) Dark bottle counts (dark carbon fixation) were subtracted 

 from the average of the light bottle samples after background 

 subtraction and quench correction. 



(2) Results are reported as net counts per minute assimi- 

 lated per milliliter per hour (cpm ml"-^hr"-^) during exposure 

 to increasing concentrations of Si02. 



(3) The reduction in carbon uptake (expressed as percent 

 of control) is reported at each concentration of 3102. 



3. Results and Interpretation . 



a. Saturation Curves . The spectral quality of light is important 

 in studies of photosynthesis (see action spectra in Jitts, et al., 

 1964); however, there is no typical submarine spectral distribution 



10 



