Occurrence and Sigyiificance of Chitino clastic Bacteria 599 



microscope at 27X magnification. An exception to tliis was found 

 in the very high chitinoclast populations in certain zooplankters, 

 which showed chitin degradation within five days. Ten to 40 

 days incubation was generally necessary for the development of 

 clear zones around colonies on chitin-yeast extract agar. 



When pure cultures of chitinoclasts from pelagic sources be- 

 came available, they were tested individually on the media used 

 for enumeration in the pelagic work. Twenty-seven cultures were 

 transferred to 2216e agar slants, incubated for three days, then 

 streaks made from each on chitin-yeast agar plates. All streak 

 plates showed good growth in twenty four hours, and the estima- 

 tions of chitin degradation are shown in Figure 2. Representative 

 responses, including the extremes, are shown in this graph. 



The medium finally selected for the enumeration of marine 

 pelagic chitinoclasts was of the following composition: 



RESULTS 



Distribution of Marine Microorganisms in Pelagic Waters 



Vertical Distribution of Aerobic Heterotrophs 



Agar plate counts of water samples from the J-Z bottle 

 casts of Cruises 1 to 4 are shown in Figure 3. The abscissa, 

 showing the average number of bacteria from duplicate plates, 

 is exaggerated decimally. 



The greatest number of pelagic heterotrophs was generally 

 found in the upper 50 meters; howe\er, relatixely low counts were 

 found in tlie upper layers on Cruises 3 and 4. 



Vertical Distribution of Chitinoclastic Marine Microorganisms 



Figure 4 shows the average number of colonies appearing 

 on chitin-yeast extract-sea water agar plates, and the number of 

 chitin-degrading microbes (those producing clear zones in the 

 chitin agar around the colonies) encircled at the appropriate 



