4. Communities of the Temperate and Cold Waters of the Southern Hemisphere . 

 (N. M. Voronina) 



The population of the pelagic zone of the temperate and polar latitudes 

 inhabit biotopes with characteristically sudden changes in environment 

 during the course of the year (see Chapter 1.2 II. 2). As we know, the 

 essence of the seasonal differences in the pelagic realm is related to 

 changes in solar radiation which, on the one hand, determine the quantity of 

 light penetrating the water, and on the other hand, the processes of heat 

 exchange, causing heating and cooling of the surface waters, formation and 

 thawing of ice and, as a result, changes in the thermal and density stratifi- 

 cation. These changes, in turn, influence the delivery of nutrient salts to 

 the euphotic layer. 



Let us take a look at how these factors are reflected in the structure 

 and functioning of the pelagic communities of the Antarctic and Subantarctic . 



4.1 Phytocenes 



Factors defining the quantitative development of phytopl ankton . In 

 Antarctic waters, the concentration of phosphates and nitrates, even during 

 the phytoplankton bloom and the period of maximum stability of the surface 

 layer, when their upward travel is hindered, remain higher than in the 

 winter in the temperate waters of the northern hemisphere. Therefore, they 

 cannot be considered as limiting factors (Hart, 1934; Bogoyavlenskiy, 1958; 

 El-Sayed, 1958b). The reason for the exceptional richness of this area in 

 nutrient salts is the constant renewal of their reserves resulting from the 

 general character of circulation of the deep water with predominance of up- 

 welling. Only the decrease in the quantity of silicates, the maximum con- 

 centrations of which are located deeper than the other biogens, may play a 

 partial role in the post-maximal decrease in the population of diatoms 

 (Clowes, 1938; Hart, 1934; Arzhanova, 1974). 



The Subantarctic is significantly poorer in nutrients; a decrease in 

 their quantity is observed as we move northward. However, even in the 

 Subantarctic, the concentration of phosphates does not drop to a level low 

 enough to limit the rate of cell division of algae in experiments (Kuenzler, 

 Ketchum, 1952; Lewin, Guilland, 1963). The addition of a mixture of nutrient 

 salts to Antarctic and Subantarctic water in experiments did not cause an 

 increase in primary production (Kabanova et al . , 1974a). It can be said 

 with certainty that in the Southern Ocean, the concentration of nutrients 

 does not limit development of phytoplankton. The inverse correlation between 

 the abundance of phytoplankton and the concentration of phosphates established 

 by Hardy and Gunter (1935) confirms this opinion quite clearly. 



Light is of dominating significance for the vital activity of algae. In 

 the higher latitudes, the total solar radiation during the course of the 

 year fluctuates widely. The time of onset of the light season and its 

 duration differ at different latitudes. The period with minimum solar 



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