Summarized data on the distribution of the population of individual 

 groups of algae are presented in Table 6. The greatest tendency to remain 

 near the surface layer is observed in the flagellates and diatoms. This 

 tendency is significantly less in the dynoflagellates, among which are 

 many obligate heterotrophs, and minimal in the Coccolithophoridae. The 

 distribution is somewhat less clear in the Subantarctic: The surface layer 

 contains a smaller fraction of phytoplankton, the population maxima are 

 located deeper. 



Table 6. The frequency of occurrence of the population maxima of various 

 groups of algae (% of number of stations) in different layers in the 

 Pacific sector of the Southern Ocean in December 1947-February 1948 (after 

 Hasle, 1969). 



Note: A = Antarctic; SA = Subantarctic. 



Ice flora . The vegetation of algae is possible not only in the open 

 water, but also in the ice. There are two maxima of development of ice 

 phytoplankton: the fall maximum, appearing on the bottom surface of the 

 ice in March-April when the thickness of the ice is about 30 cm, and the 

 spring maximum, arising in October at a depth of more than 1 m (Hoshiai, 

 1972). The ice flora is usually localized in the water-snow and congelation- 

 ice layers (Oradovskiy, 1973). The composition of diatoms differs in these 

 two layers and, apparently, is determined by the time of settlement. An 

 eponic group is distinguished, including attached species of the genera 

 Pleurosiqma , Nitzschia , Amphiprora , Fragilaria , and a permanently plank- 

 tonic group, living among the ice crystals: Biddulphia , Coscinodiscus , 

 Asteromphalus (Bunt, Wood, 1963). The main group of this algae are diatoms. 

 Their number in this biotope may be very high: up to 5-40-106 cells/1, 

 while under the ice it is extremely low (Bunt, 1963, 1968). The ice 

 community lives under extreme conditions: The content of nutrient salts is 



86 



