ZoBell 



— 62 — 



Marine Microbiology 



tions up to several hundred miles from land. However, the bacterial 

 population of the water collected from the pier and at other near-shore 

 stations increases during and following periods of land drainage. Also 

 when strong currents or turbulent seas stir up bottom deposits or carry 

 in seaweed, many more bacteria are found in the water. Gee (1929) has 

 commented on the more or less oceanic conditions near the Scripps Insti- 

 tution as indicated by the bacterial flora. The average annual rainfall in 

 this region is only about 11 inches. 



Table XIII. — Average number of bacteria per ml. of sea water collected at different distances 

 from land in the vicinity of the Scripps Institution of Oceanography, La Jolla, California {from 

 ZoBell and Feltham, 1934): — 



Entirely different conditions occur in the water of nearby Mission Bay 

 and San Diego Bay. Water in these arms of the ocean contains from 

 thousands to millions of bacteria per ml., and the microflora differs quali- 

 tatively as well as quantitatively from the oceanic microflora. Going 

 seaward from San Diego Bay, the bacterial content of the water decreases 

 with distance from land as shown by the data in Table XIV. 



Table XIV. — Average number of bacteria per ml. of sea water collected while traveling sea. 

 ward from San Diego Bay at low tide: — 



The distance from land to which land drainage influences the bacterial 

 population of sea water is primarily a function of the volume of drainage, 

 oceanic circulation in the region, and the depth of the water. The ter- 

 restrial influence is noticeable far from the mouths of large rivers like the 

 Columbia or the Amazon. The influence of the latter extends nearly 200 

 miles from land at certain times. Warm fresh water of low density mixes 

 very slowly with non-turbulent sea water. 



The wind often carries large numbers of soil microorganisms and other 

 materials into the sea (ZoBell, 1942c), but the effect of wind-borne ma- 

 terial on the bacterial population of sea water is negligible as compared 

 with that of land drainage. 



The decreasing abundance of bacteria with distance from land is not 

 peculiar to the marine environment. A similar horizontal distribution of 

 bacteria has been noted in fresh-water lakes, which indicates that factors 

 besides salinity are responsible for the death of bacteria carried into large 

 bodies of standing water. 



Bacterial counts were about 200 times as great at the mouth of the 

 main river flowing into Lake Windermere, England, as in samples of water 



