132 Marine Microbiology 



bacterial growth. Bacterial growth was inhibited in cultures of 

 the diatoms Nitzchia closterium. Thalassionema nitzchioides, 

 Cerataidina bergonii, and of the dinoflagellates Prorocentrum 

 micans, Gymnodinium wulfii. In the cultures of the diatoms 

 Leptocylindrus danicus, Skelefonema costatum, Chaetoceros 

 socialis, Ch. ciirvisetus, Ch. Joiidehi this inhibition was not so 

 clear. In the cultures of Coscinodiscus sp. a parallel development 

 of algae and bacteria was observed. Bacteria which grew on 

 agar plates were representative of saproph>^tes widespread in 

 the Black Sea: Pseudobacterium subluteum, Chromobacteriiim 

 rhenii. Bacillus idosiis and some others. There was no observ^ed 

 correlation between defined species of algae and bacteria. 



CONCLUSION 



The algae with a marked seasonal prevalence of development 

 have a higher fission rate and a shorter period of intensive 

 multiplication. Seasonal forms have periods of rest, while the 

 year-long fomis have a period of rest which is less distinct. 

 However, the year-long forms of phytoplankton have maximal 

 development at different periods of a year (spring, summer or 

 autumn). The observed biological cycle is apparently the result 

 of physiological changes in the cell itself. For the Black Sea the 

 development of many fomis of phytoplankton is throughout the 

 year with distinct spring, summer and autumn maxima. From the 

 average monthly fission rate of the plankton algae (Table 2), 

 it is possible to conclude that besides the diatoms, the dinoflagel- 

 lates and small flagellates play a great role in the productivity 

 of the Black Sea. 



Correlation between the number of cells of algae and that 

 of bacteria may change during the year according to the system- 

 atic composition, and especially to the physiological condition 

 of the phytoplankton. 



