Fission Rate of Plankton Algae of the Black Sea in Cultures 129 



Skeletonema costatum, Leptocylindriis daniciis, Cerataiilina Ber- 

 gonii, Thalassionema nitzschioides, Prorocentrum micans, Exuvia- 

 ella cordata, Peridinium trochoideinn, Peridinium triquetum, 

 Gymnodinium wuljii, and others. Monocultures of the pigmented 

 small flagellates, Chlamydomonas minima, and Carteria wiUei 

 were the first grown from the Black Sea. 



The division rates differ for the various species of plankton 

 algae (Table I). Among diatoms durmg mass blooms Skeleton- 

 ema costatum has the highest division rate (3 hours) and Cos- 

 cinodisciis fanischii the lowest (30 hours). Among dinofiagellates, 

 Peridinium triquetrum was notable for the greatest division rate 

 (10 hours), and Ccratiuui furca for the lowest (48 hours). 

 Carteria willei had the greatest division rate (6 hours) among 

 the small flagellates. 



The division rate in cultures of the same species of algae 

 varies markedly during the year. For Skeletonema costatum it 

 varied from three hours (maximum) in April-May to 56 hours 

 (minimum) in November; for Chaetoceros socialis from 8 to 84 

 hours; (maximum in May, minimum in February); for Leptocy- 

 lindrus danicus from 11 to 65 hours; (maximum in August-Sep- 

 tember, minimum in November-December); for Prorocentrum 

 micans from 12 to 127 hours (maximum in July- August, minimum 

 in January); for Peridinium triquetrum from 12 to 50 (maximum 

 in April-May, minimum in July); for Exuviaella cordata— horn 

 15 to 90 (maximum in August, minimum in December); for 

 Chlamydomonas minima from 12 to 120 hours (maximum in 

 July, minimum in December). 



The division rate of the predominant species slows down 

 markedly as their blooms decrease. Therefore the average 

 monthly division rate has lower values than the minimum ones 

 (Table 2). 



As a rule, the neritic seasonal forms, giving in the sea a 

 short burst of bloom, have the highest division rate. Such species, 

 in spite of the high content of nutrients in experimental cultures 

 often die off, form auxospores or resting stages after reaching 

 maximum division rate. 



The highest division rate of cells in cultures is usually ob- 

 served in the period of the observed numerical maximum of 



