spring, if insolation is sufficient, but stratification is not stable, 

 the phytocenosis is subject to such great losses--transport of cells from 

 the euphotic zone by turbulent mixing--that the avalanche-like bloom of 

 phytoplankton does not occur. 



Soon after the peak of the pulse, the phytoplankton begins to die, 

 the water becomes rich in suspended and dissolved organic matter, which 

 serves as the basis for the development of masses of bacteria and protozoa-- 

 the heterotrophic flagellata and infusoria (Sorokin, 1974; Pasternak, 

 Shushkina, 1973). It is this "protonutriment" in the surface layers above 

 the thermocline which serves as the food base for most of the herbivorous 

 plankton, the quantity of which tends to increase rapidly, reaching its 

 maximum 1-3 months after the beginning of the bloom. The biomass of the 

 predators reaches its maximum later, and their pressure on the herbivorous 

 plankton differs in different regions and, apparently, experiences signifi- 

 cant annual fluctuations. 



The developing community changes not only with time, but also, 

 following the currents, moves in space. Since stratification (the develop- 

 ment of the seasonal thermocline) may not occur simultaneously in different 

 regions, even though they be close together, the communities in different 

 areas in the moving water may be in different stages of maturity later on. 

 However, these differences, even over large regions, are generally not 

 great, so that the beginning of the spring pulse, over the great, hydrologi- 

 cally homogeneous areas of water, fluctuates within a narrow interval of 

 time. The intensity of consumption of phytoplankton by zooplankton, even 

 within the limits of a single zone or a single community, is also not uniform 

 over the entire water area (Heynrih, 1957; Kashkin, 1962; Kamshilov et al . , 

 1958; and others). As a result, the picture of distribution of plankton is 

 always rather variegated in both the space and the seasonal respects. 



2.2 Communities of the Tropical Regions 



In the tropics, where seasonal cooling of the surface water is slight 

 or nonexistent, winter convection does not occur. Enrichment of the surface 

 layers with nutrients occurs primarily in areas of quasi-steady upwelling of 

 water, caused by hydrodynamic factors (zones of divergence of currents, 

 upwelling of water near the shores of continents, resulting from onshore 

 winds, the influence of islands and underwater banks). Studies performed 

 on special cruises of the VITYAZ have allowed us to construct a schematic 

 diagram of the circulation of nutrients in the ecosystem of the active 

 layer of the pelagic zone of the tropic ocean, which determines the picture 

 of development of its community (Vinogradov et al . , 1971). 



In a zone where the water ascends, the pycnocline is close to the 

 surface, nutrients penetrate into the surface layer, and development of 

 phytoplankton begins in this layer. The water flows outward from the 

 upwelling zone. Temperature (density) stratification of the layers of 

 water becomes more precise, intermixing decreases and the upper boundary of 

 the thermocline descends. Nevertheless, nutrients, as a result of turbulent 

 intermixing, continue to reach the upper, mixed layer, from below, though in 

 decreasing quantities (Fig. 1). This flux of nutrients from below is 



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