were very carefully covered with black tape to 

 exclude all light. An attempt to obtain dark 

 bottles by spraying with black paint failed to 

 produce light-tight bottles since very small 

 holes in the painted surface permitted light 

 to pass. The bottles were incubated in an 

 illuminated water bath (fluorescent lighting 

 through a glass bottom) in a random distribu- 

 tion. Illuminance was measured with a Weston 

 856 YE photocell connected to a 0-100-micro- 

 ammeter having a 50-ohm internal resistance. 

 The meter was calibrated against a Weston 

 model 756 laboratory illumination meter. 

 Illuminance measured at the glass bottom of 

 the water bath was 1100 to 1550 foot-candles. 

 The average illuminance in the bottles was 

 about 8o"/ of this figure. This average 

 illuminance was about 33°/o of saturation if 

 saturation illuminance is taken to be 3200 

 foot-candles (Steemann Nielsen, 1952), or was 

 53°/o of saturation if Ryther's (1956) average 

 value for 1*4- different phytoplankton species 

 (2000 foot-candles) is used. 



Just before the bottles were placed in the 

 water bath (zero hour) and after each in- 

 terval of time, an appropriate aliquot of the 

 sea-water sample was removed with a sterile 

 pipette and plated in duplicate for each 

 bottle in sterile plastic petri dishes on a 

 peptone-yeast extract agar (Oppenheimer and 

 ZoBell, 1952). The bottles were shaken 

 thoroughly before the sample was removed for 

 the pour-plate determination. The plates 

 were poured with agar at k2 _ 2°C on a sus- 

 pended table which was steadied in moderate 

 seas with the aid of another person. One 

 person could operate the suspended table in a 

 calm sea, whereas pouring plates was imposs- 

 ible in a heavy sea. The plates were incubated 

 in the dark at 31 ± 1°C for three days and 

 then examined with a Quebec colony counter for 

 the heterotrophic marine bacterial count. 



The water sample from each bottle was filtered 

 through a Millipore HA filter (0.k5 ± 0.02 micra 

 Millipore Filter Corporation, Watertown, Mass.) 

 which retained all of the plankton and most of 

 the bacteria in the samples. The filters were 

 washed with nonradioactive sea water, dried in 

 a desiccator over silica gel, and the radio- 

 active count determined in a proportional flow 

 counter (Nuclear Measurement Corporation, PC-1) . 



RESULTS 



Experiments were conducted to determine the 

 increase in bacterial numbers, and Cl^ 

 assimilation over an l8-hour period in 

 bottles that were cleaned and in bottles 

 that were cleaned and sterilized. Surface 

 sea water was collected at 17°5^' N latitude, 

 103 o 50' W longitude (BT Station 3-5) and 

 incubated in light bottles for 0, 1, 2, k, 

 8, and l8 hours at 30 t 1*C (sea-surface 

 temperature, 28.8°C) in the illuminated (1250 

 j| 150 foot-candles) water bath. The results 

 of this experiment appear in Table 8. 



The data from a similar experiment for surface 

 sea water collected at ll°4l' N latitude, 

 91°52' W longitude (BT Station 7 - 5), in- 

 cubated under identical conditions for 0, 2, 

 h, 6, 8, 13, and 18 hours is presented in 

 Table 9. 



Ik 



While C assimilation was slightly higher in 



the autoc laved bottles throughout most of 

 the experimental period, this difference is 

 not significant. Bacterial growth was lower 

 in the autoclaved bottles in the early parts 

 of the experiments (up to 13 hours), but was 

 greater at 18 hours. The reason for the 

 higher bacterial population in autoclaved 

 bottles at the end of the experiment is not 

 clear, but may be due to release of nutrients 

 by autoclaving the bacteria originally present, 

 or to possible "antibiotic" activities of the 

 original bacteria. However, autoclaving does 

 not appear to be necessary in carrying out 

 a production determination, since the 

 C-*- values are not significantly different 

 during the customary experimental period 

 (8 hours or less) . 



An experiment to determine bacterial increases 

 and carbon dioxide assimilation for a more 

 prolonged period using the C^ fixaction 

 method in both light and dark bottles was 

 , carried out using surface sea water from 

 19°08' N latitude, 105°29' W longitude 

 (BT Station 23-6). The 250-ml. reagent 

 bottles were filled completely with sea water 

 and NaHC 1 ^, (k uc) was added carefully with 

 a syringe. Immediately after filling with 

 sea water, the bottles were sampled for their 

 bacterial counts by the pour-plate technique. 



80 _ 



