Chapter V 



— 65 — 



Distribution in the Sea 



(Clarke, 1933). Likewise it is conceivable, although not demonstrated 

 by lield data, that the growth of bacteria may be influenced by diurnal 

 fluctuations in the activity of photosynthctic organisms in the euphotic 

 zone. In fact, there are several indirect ways in which sunlight could 

 influence the abundance of bacteria in sea water throughout the day, but 

 there is no experimental evidence to prove that sunlight has a direct effect 

 upon the bacterial population of sea water (see section on the Effects of 

 Solar Radiations on page 69). 



Vertical distribution of marine bacteria : — In the mid-Atlantic Ocean, 

 Fischer (1894a) usually found more bacteria at depths of 200 to 400 

 meters than in water near the surface. Hardly any bacteria were found 

 at depths exceeding 1000 meters. Fischer examined samples from depths 

 as great as 5250 meters, but his quantitative results are of questionable 

 validity because he used a brass cylinder with open ends for collecting 

 many of his samples. He reported that Bassenge found bacteria to be 

 most abundant a few meters below the surface in the North Atlantic 

 Ocean and Caribbean Sea. Details concerning the technic used by Bas- 

 senge are not available. 



Using an evacuated glass bulb for the collection of samples in the Gulf 

 of Naples, Russell (1891) found about as many bacteria at a depth of 

 1 100 meters as in surface water. Likewise no variation in the vertical 

 distribution was noted in the shallow water in the Cape Cod region where 

 Russell (1893) analyzed samples from depths up to 140 meters at sta- 

 tions up to 120 miles from land. Water movements in this region tend to 

 prevent stratification. 



Just off the coast near Oran, Algeria, Cassedebat (1894) noted an 

 abrupt decrease in the bacterial content of water with increasing depth. 



The number of bacteria found at different depths in the open Atlantic 

 Ocean between Portugal and Brazil by Otto and Neumann (1904) is given 

 in Table XVI. It is unfortunate that these workers failed to coUect sam- 

 ples from depths intermediate between 5 and 50 meters. More recent 

 work suggests that it is in these intermediate depths where the maximum 

 bacterial population might have been found. 



Table XVI. — Bacteria per ml. of water from different depths aiid stations in the Atlantic 

 Ocean {from Otto and Neumann, 1904): — 



During prolonged periods of calm weather, Schmidt-Nielsen (1901) 

 often noted the presence of twice as many bacteria in water at a depth of 

 25 meters as in surface waters of the North Sea between Oslo and Stav- 

 anger. He found bacterial stratification to be more marked in fjords than 

 in unprotected water. Stratification is obliterated when the sea is rough. 

 Although Schmidt-Nielsen presented no data to prove his contention, he 

 believed that when the sea was absolutely calm, differences might be 

 found in the bacterial content of the very topmost layer and strata a few 

 millimeters below the surface. 



