ZoBell — 60 — Marine Microbiology 



in the number of bacteria in samples of sea water taken from the same 

 spot." Russell (1893) also observed that an occasional sample of sea 

 water yielded unexpectedly high numbers of bacteria. 



This unevenness in the distribution of bacteria in water is due partly 

 to the occurrence of relatively large numbers of bacteria aggregated in 

 clumps or associated with particulate matter. Vigorous shaking prepara- 

 tory to analyzing the samples separates some of the bacteria in such 

 clumps, thereby increasing the number detected by plating procedures. 

 The number of bacteria constituting clumps and their separability by 

 shaking are both variables which contribute to the unevenness in the 

 distribution of bacteria. The decomposing remains of a small organism 

 such as a copepod or a dinoflagellate may harbor scores of living bacteria. 

 Also the presence of a school of fish or the defecation of some marine ani- 

 mal may cause large, though temporary, increases in the bacterial popu- 

 lation in localized areas. 



Taylor (1940) has observed in lakes marked fluctuations in the num- 

 bers of bacteria which bore no relation to fluctuations in the concentration 

 of dissolved substances or other factors. He noted a semblance of cor- 

 relation between high bacterial counts and periods of rainfall, and some 

 relation existed between the total numbers of phytoplankton and the bac- 

 terial populations of water samples. 



The distribution of other planktonic organisms with which bacteria are 

 intimately associated is also uneven. After observing the uneven distri- 

 bution of diatoms and dinoflagellates in sea water in his studies on the 

 range of error in microenumeration, Allen (1921) stressed the need of 

 many samples and the importance of the continuity of collections. From 

 evidence accumulated over a period of thirty years, Allen (1941) con- 

 cluded that the uniformity of distribution of plankton in sea water is 

 practically nonexistent at any time. The reasons for the occurrence of 

 plankton organisms in swarms or sporadically are not well understood. 

 The relations between bacterial and other plankton populations are dis- 

 cussed elsewhere in this volume. 



Distance from land : — The largest bacterial populations usually occur 

 in sea water near land regardless of the depth or temperature of the water. 

 According to Fischer (1894a), harbor water often contains more than a 

 million bacteria per ml. Inland seas generally contain more than 500 

 bacteria per ml., and waters from the open ocean, four or more kilometers 

 from land, generally contain fewer than 250 bacteria per ml. Larger bac- 

 terial populations were observed by Fischer in the open ocean beyond 

 the direct influence of the coast where there was a convergence of cold 

 nutrient-rich water and warmer water. Also he noted bacterial popula- 

 tions exceeding 1000 per ml. associated with seaweeds in the Sargasso Sea. 

 M"';In the Gulf of Naples, Sanfelice (1889) noted a marked decrease in 

 the bacterial population at greater distances from land. This observation 

 led him to conclude that bacteria are not indigenous to the marine environ- 

 ment but rather passive inhabitants from the land. 



Cassedebat (1894) found thousands of bacteria per ml. in harbor 

 water of Oran, Algeria, compared with only 33 per ml. two kilometers 

 from land. 



Gazert (19066) made similar observations in the South Atlantic and 

 Antarctic Ocean where the largest bacterial populations were found either 

 in the vicinity of land or seaweeds. Seaweeds are usually most abun- 



