Chapter V 



FACTORS INFLUENCING THE DISTRIBUTION 

 OF BACTERIA IN THE SEA 



A multiplicity of interrelated factors are known to be responsible for 

 the number and variety of microorganisms found in an environment as 

 complex as the sea. Therefore it is difhcult to appraise quantitatively any 

 one factor. The dynamic character of the marine environment further 

 complicates the problem. Water masses are moving continuously. A 

 water mass which is here today may be ten miles away tomorrow. 



Cognizance must be taken of the fact that the number of microorgan- 

 isms found in a given environment at any particular time is the resultant 

 of the forces which influence the reproduction and those which cause the 

 death of microorganisms. In spite of the existence of optimal conditions 

 for the reproduction of bacteria in a given environment, the bacterial pop- 

 ulation may be very low if conditions for survival are unfavorable. On 

 the other hand, where certain environmental conditions are optimal for 

 the prolonged survival of bacteria, large populations may occur, notwith- 

 standing exceedingly slow rates of reproduction, growth, and activity. 



It is reiterated that, due to the widely divergent analytical procedures 

 which have been employed in studies of the distribution and activities of 

 marine bacteria, the quantitative results reported by different workers in 

 different parts of the world are not directly comparable. 



Fluctuations in numbers of microorganisms : — Although, compared 

 with land, the marine environment has a relatively high uniformity in 

 chemical composition and other properties, bacteria are not evenly dis- 

 tributed in the ocean. Besides variations in the diurnal, seasonal, vertical, 

 and geographical distribution of bacteria in the sea, detectable dififerences 

 occur in the bacterial population of samples collected at the same time 

 and place. If, however, enough samples of sufficient size are analyzed, 

 these local differences in the abundance of bacteria may be greatly min- 

 imized. 



By carefully analyzing a large number of samples of sea water col- 

 lected at one locality, ZoBell and Feltham (1934) found that the average 

 deviation of duplicate plate counts on the sarrie well-shaken water sample 

 was 7.8 per cent, the range being o to 26.6 per cent. The analysis of ten 

 lo-ml. samples collected at one place within a few seconds of each other 

 showed an average deviation of 85.3 per cent from the average plate count 

 on all of the samples, the range being 12.1 to 155.8 per cent. When only 

 i.o-ml. samples collected directly from the ocean were plated, the counts 

 on individual samples deviated by as much as 900 per cent from the mean, 

 or in other words from 18 to 20 times as many bacteria were found in 

 some I.o-ml. samples as in others collected at the same place. The aver- 

 age deviation from the mean of loo-ml. samples was only 29.4 per cent, 

 the range being 12.7 to 74.9 per cent. 



After finding from 2 to 83 bacteria per ml. of sea water in ten different 

 samples collected seriatim from the same depth at a single station, 

 Reuszer (1933) concluded that "considerable variation may be expected 



