Distribiilion of Heterotrophic Baeteria 555 



smallest bacterial population. Here, sterile samples of water have 

 been found most often (14.3%), while 20 per cent of the samples 

 contained single numbers of bacteria (from 1 to 10), and 37.1 per 

 cent contained from 11 to 100. The maximum figure was 382 

 colonies. 



A comparison of the quantitative distribution of saprophytic 

 bacteria at various depths with the vertical distribution of tem- 

 perature and salinity does not show any direct relation with these 

 factors; this confirms previous observations by us for other sea 

 basins (11, 12). On the whole, for the vertical distribution of 

 heterotrophs in the Mediterranean Sea, as for other seas and 

 oceans, microzones are typical. It reflects the distribution in the 

 water of forms of organic matter available for these organisms 

 (9, 11). However, there is at the same time a general scheme; 

 that is, the presence at any horizon of more or less sharp increases 

 in bacterial numbers in comparison with adjacent horizons. The 

 minimum most often occurs on 10-50 or 50-75, 250, 400 or 500 

 (seldom 750), 1250 or 1500, 2000 or 2500, 3000 or 4000 m. The 

 maximum is usually observed at 0, 25, 100 or 100-150 (seldom 

 200), 300 or 400, 500 or 750, 1000 or 1250, 1500 or 2000, 2500 m. 



One may observe a certain lack of maximum and minimum 

 zones relative to each other on the horizons of some stations 

 deeper than 250 m. The minimum at 10, 50 and 250 m; and the 

 maximum at 0, 25 and 100 m are observed with the highest ac- 

 curacy and highest frequency. 



As is known, the quantitative distribution of heterotrophic 

 microorganisms gives a picture of the distribution of available 

 forms of suspended and dissolved organic matter, which, in 

 turn, are determined by the hydrological regime of the basin (9). 

 Therefore, one can say with confidence that the typical regularity 

 of the quantitative distribution of heterotrophic bacteria, as here 

 reported, is a reflection of the hydrological structure of the re- 

 gions of the Mediterranean Sea under investigation. In Table 1, 

 the Mediterranean Sea is compared with other seas and oceans 

 with respect to the quantitative distribution of saprophytic bac- 

 teria as studied by the filter method. It is seen that the number 

 of heterotrophs in the Mediterranean basin considerably exceeds 

 those found in the regions of the North Pole, the Greenland Sea, 



