, tZDO 



Fig. 4. Change of total biomass of living elements of a pelagic 

 ecosystem from the tropical regions of the ocean in the 0-150 m layer: 

 P--phytoplankton; f^--Protozoa; b--bacterioplankton; ^2." 

 microzooplankton; f3, f/i--fine and coarse herbivores; Sj--Cyclopoida; 

 S2--carnivorous Calanoiaa; S3--Chaetognatha and Polychaeta. 



insufficient for intensive development of phytoplankton. A situation 

 was created in which the lower maximum "separated" from the thermocline, 

 and its position was subsequently determined by the lower limit of 

 illumination and the flow of nutrients from deeper levels. 



With still more mature state of the community (over 60-80 days), in 

 the oligotrophic and ultraoligotrophic regions, according to the model, 

 almost complete disappearance of the upper maximum of all elements 

 should occur. Actually, the upper maximum disappears only for the 

 phytoplankton, continuing to exist for the zooplankton even in 

 oligotrophic regions. An analogous picture is yielded by several 

 modernized versions of this r-.odel (Vinogradov et al., 1975). 



The results produced show that many of the existing features of 

 vertical and time distribution of elements in the pelagic ecosystem of 

 the tropical regions of the ocean can be quantitatively reproduced and 

 explained by means of the model described. However, many important 

 aspects of the functioning of pelagic ecosystems still remain outside 

 the model. The assumption of constancy of the velocity vector of a 

 current in the 0-200 m layer and resulting absence of horizontal 

 displacements hardly agrees with the picture actually observed in the 

 ocean. Finally, the model developed fails to consider the final trophic 



331 



