2. The Spatial-Dynamic Aspect of Existence of Pelagic Communities 

 (M. E. Vinogradov) 



Due to the mobility of the biotope, the water, pelagic communities 

 differ significantly in their structural and functional characteristics 

 from other marine communities, and the analysis of their development from 

 this standpoint is of particular interest. 



In the volume on "The Biologic Structure of the Ocean," in the chapters 

 dedicated to the bioqeography of pelagic animals and their distribution, it 

 was stated that the bases of the areas of distribution of most species in 

 the pelagic zone are related to quasi-steady circulation of the waters, 

 usually including not only horizontal motion, but also vertical motion. The 

 circulation may have various dimensions and various degrees of "openness." 

 Sometimes, preservation in the circulation of but an insignificant portion 

 of a population supports reproduction and the existence of the species 

 with its area of distribution, even though most of the population is scattered 

 and unproductively lost. 



The great oceanic or shoreline circulations form the basis for the area 

 of distribution of many planktonic species which, together with species 

 transported from other circulating currents or entering a given circulation 

 for a time as a result of vertical and horizontal (nektonic forms) 

 migrations, make up the community of a given region. 



The biotope of a community--the aquatic medium--is continually renewed, 

 while its characteristics change regularly as a result of seasonal or 

 hydrodynamic factors. The community populating the water also undergoes 

 regular changes. 



2.1 C ommunities in Cold-Water Regions 



In regions with a clearly expressed seasonal cycle, changes are 

 determined primarily by this cycle. They will be analyzed in greater 

 detail in Chapter II, paragraphs 2-4; here, we will briefly discuss certain 

 aspects, in order to show that the development of pelagic communities of 

 cold-water and tropical regions of the ocean follows, on the whole, the 

 same regularities. 



In temperate and cold-water regions, the enrichment of the surface, 

 euphotic layers with nutrient salts occurs primarily due to winter convection 

 extending into the layer beneath the euphotic zone, where the concentration 

 of nutrients is high throughout the year. The winter minimum in the 

 development of phytoplankton is followed by the spring pulse, resulting 

 from the increase in the intensity of solar radiation and, no less signifi- 

 cantly, the development of stable stratification of the water above the 

 basic pycnocline. 



When the seasonal pycnocline develops, the bloom of phytoplankton may 

 sometimes even begin beneath the ice (Konovalova, 1972), whereas in the 



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