Chapter V — 89 — Distribution in the Sea 



as peptone or glucose for the multiplication of marine bacteria is between 

 looo and 10,000 mgm. per liter of sea water. This is 200 to 2000 times the 

 concentration of organic matter in sea water, and only a small fraction of 

 the latter is readily utilizable. This emphasizes that the concentration of 

 organic matter in the sea is decidedly sub-minimal for bacterial activity. 

 The addition of as Httle as o.i mgm. of utilizable organic matter to sea 

 water results in increased bacterial activity. Up to 100 mgm. per liter, 

 doubling the concentration of organic nutrients approximately doubles 

 the rate of bacterial multiplication. 



Although it is difficult to appraise quantitatively each of the numerous 

 interrelated factors which influence the distribution of bacteria in the sea, 

 the organic content of water is certainly one of the most important factors. 

 Increases in the availability of organic nutrients in sea water are almost 

 invariably accompanied by increased bacterial populations. The low con- 

 centration of organic nutrients and the lack of soUd surfaces for concen- 

 trating organic nutrients are believed to be the principal factors which 

 account for the small number of bacteria found in the sea. Wherever 

 there is an influx of organic matter or an increase in the amount of sus- 

 pended particles caused by land drainage, stirring up of the bottom, the 

 activity of photosynthetic organisms, the appearance of seaweeds, fisher- 

 ies activities in localized areas, upwelling, or convergence of cold and warm 

 water which kills many organisms, bacteria are found in greater num- 

 bers than in surrounding water. 



While the numbers of bacteria which may develop in sea water stored 

 in the laboratory are directly proportional to content of utilizable organic 

 matter, the bacterial population of sea water in situ is not necessarily in- 

 dicative of the organic content of the water. A large bacterial population 

 may more effectively utilize the organic content of sea water and reduce 

 it to a lower level than a few bacteria, in which case there would be rela- 

 tively little organic matter in the presence of large numbers of bacteria 

 until the latter perish. The bacteria themselves contain very little or- 

 ganic matter, it requiring a bacterial population of about 10,000,000 per 

 ml. to be equivalent to i .0 mgm. of organic matter per liter. On the other 

 hand, in certain regions there may be enough organic matter to provide 

 for the rapid multiplication of bacteria, but the population may never 

 exceed more than a few thousand per ml. due to the activities of predators 

 or other factors inimical to the prolonged survival of bacteria. 



