78 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



autoclaved sea water before it had cooled com- 

 pletely, precipitates still formed. 



The three solutions used in the preparation of 

 this culture medium were — 



Solution A.. KN0 3 20.2 grams. 



Distilled water To make 100 cubic 



centimeters of 

 solution. 



Solution B-. MgSO* 4 grams. 



CaCl 2 4 grams. 



Fe(NH 4 ) (S04) 2 — - 1 gram. 



HC1 (cone.) 2 cc. 



Distilled water To make 100 cc. of 



solution. 



Solution C- KH 2 P0 4 1.53 grams. 



Distilled water To make 100 cc. of 



solution. 



Particulate matter was first removed from the 

 sea water by filtering it through cotton. Then, 

 0.55 cc. of solution A and 0.50 cc. of solution B 

 were added to each liter of sea water. This 

 medium was autoclaved and, after cooling com- 

 pletely, 0.50 cc. of solution C, which had been 

 autoclaved separately, was added aseptically. 



CULTURE PROCEDURE 



Nitzschia closterium was isolated into pure 

 culture and used in these experiments. It was 

 maintained in pure culture on agar containing 2 

 percent glucose and 0.5 percent peptone in addi- 

 tion to Miquel's inorganic nutrients. Tests for 

 purity were not made on cultures during or after 

 the experiments since sterile techniques and 

 inorganic media were used and since most experi- 

 ments were completed within a short period of 

 time. 



The cultures were grown in a refrigerated 

 cabinet (fig. 1) at a temperature of 20° ±2° C. 

 The cabinet was equipped with adjustable wooden 

 shelves to each of which six 40-watt daylight 

 fluorescent lights, spaced 2 inches apart, were 

 attached. Approximately 2 inches above the 

 lights were glass shelves upon which the cultures 

 were placed. 



PHOSPHORUS MEASUREMENTS 



The radioactive phosphorus used in these 

 experiments came from Oak Ridge National 

 Laboratory. 1 Activity was determined by means 

 of a conventional dip-type Geiger-Miiller counting 

 tube connected with a scaler-of-64 circuit. The 



1 Supplied on authorization from the Isotopes Division, United States 

 Atomic Energy Commission. 



Figure 1. — Culture cabinet showing illumination of 

 cultures. 



geometry was constant, and corrections for decay 

 and coincidence loss were made. The radio- 

 active phosphorus was standardized by comparison 

 with a simulated standard of known microcurie 

 strength. Inorganic-phosphorus concentrations 

 were determined by the Atkins-Deniges molybdate 

 method as modified by Wattenberg (1937). Salt- 

 error corrections were made and algal cells were 

 removed by filtering before making determina- 

 tions. The intensity of the blue color was meas- 

 ured with a Klett-Summerson photoelectric color- 

 imeter which had been standardized with solutions 

 of known phosphorus content. Klett filter No. 66 

 and a 4.5 x 2.5 centimeter cell were used. Since 

 the intensity of the blue color changes with time, 

 determinations were made approximately 10 

 minutes after the addition of reagents. The con- 

 centration of phosphorus is expressed as micro- 

 gram atoms of phosphate phosphorus per liter 

 (/xgAP/L) as recommended by the International 

 Association of Physical Oceanography (Sverdrup, 

 et al. 1942, table 34). 



DETERMINATION OF POPULATION SIZE 



The number of cells per liter was determined 

 by removing approximately 5 cc. of medium 

 after vigorously shaking the culture to distribute 

 the cells evenly throughout the medium. The 

 average of two cell counts, made with an improved 

 Neubauer haemocytometer, was taken as the 

 population size. A careful check has shown that 



