196 Marine Microbiology 



Febniaiy, 1960 to January, 1961, Every month samples of water 

 from different depths, especially at the stations A and C were 

 collected from the stations B, D, E ( Fig. 1 ) . Such samples were 

 taken each 5 meters of deptli. In the transition zone between the 

 upper layer containing oxygen and the lower one containing 

 hydrogen sulphide, samples were taken out at 1 meter or every 

 half meter depth. 



Measurements of pH, analyses of dissolved oxygen by the 

 Winkler method, and of hydrogen sulphide by iodometric titra- 

 tion method, were carried out. Water temperatures were also 

 recorded. 



For counting sulphate-reducing bacteria the methods of 

 Grossman and Postgate (8) and especially the method of Senez, 

 Pichinoty and Geoff ray (9) for the waters of Gasometers were 

 used. I used the culture technique of 'shake* agar previously 

 employed by Genovese, Pichinoty and Senez (7). The occurrence 

 of the purple sulphur-oxidizing bacterial floral in the sediments 

 and water was confirmed in laboratory by the Winogradsky 

 culture-aquarium. The glass-stoppered cylinders containing the 

 cultures were exposed to the sunlight at the temperature of the 

 laboratory. 



RESULTS 



As already stated, I had previously noticed that the transi- 

 tion zone between the higher layer containing oxygen and the 

 lower one containing hydrogen sulphide was situated at a depth 

 of 12 m. In the course of the present investigations, the zone did 

 not maintain a constant depth, but it had some very remarkable 

 shifting. 



During the early months of the investigation, from February 

 up to July, the transition zone remained at a depth between 8 

 and 9 m (Fig. 2); in August it shifted up to level 1.5 m, and 

 then during the remaining months of investigation, it shifted 

 downwards again to deeper levels, varying between 11 and 14 m. 



Notice that during the months from April to July, that is 

 during the samplings made on 4 April, 4 May, 9 June and on 

 4 July 1960, the tiansition zone, at station A, stayed at a constant 

 depth of 8.5 m. Dining this period the phenomenon of "red 

 water" was observed in the zone lying immediately below. I had 

 recendy occasion to refer this phenomenon to the 17th Sym- 



