Spring 



Fig. ' •-casonal changes in vertical structure of a C' 'ininity. The 

 diagram ^mo^.s the positions and spread of the core of tne populations of 

 C alanoides acutus ( 1 ) , C alanus propinquus ( 2 ) , and .R hincalanus gigas ( 3 ) 

 TVoronina, 1972). 



This cycle is illustrated schematically in Fig. 18. This restructuring 

 of the vertical distribution of plankters during the course of the vege- 

 tation season occurs at e\/ery point in the water area. It is based on 

 the changes in the vertical structure of the populations and the asynchronism 

 of their life cycles described earlier. The earlier occurrence of each 

 phase of the cycle in the northern latitudes, in comparison to the southern 

 latitudes^ means that the same sequence of structures will be observed 

 along a single meridian as we move from south to north. 



The maxima of biomass of these species is observed in different 

 places in space as a result of the asynchronism of the periods of dominance 

 of the fourth and fifth copepodite stages in the various populations. 

 (During the period of dominance of these stages the greatest biomass 

 concentration is achieved.) As a result, the summer maximum of C_. acutus 

 is always located further south or deeper in the water than that of C^. 

 propinquus , while that of R. gigas is further north than that of the 

 other two species (Fig. 19"). A similar divergence of the biomass maxima has 

 been observed in Subantarctic copepods. 



The spatial distribution of locations of maximum concentrations 

 of various species is also characteristic for chaetognaths (David, 1958, 

 1965) and euphausiids. Apparently, here also, it is determined by the 

 asynchronism in the life cycles (Timonin, 1968). In this manner, 

 competitive interrelationships between similar species are minimized. 



The annual cycle in the pelagic zone . The cycles of individual 

 populations, partially overlapping in time, combine to make up the 

 seasonal changes in the total quantity of zooplankton. The quantity of 

 zooplankton in the upper 100 meter layer is characterized (Fig. 20) by 

 two maxima over the course of the year (Foxton, 1956; Voronina, 1970a, b). 

 The first, smaller, maximum is related to the spring ascendance of 

 organisms into the euphotic layer; the second to the development of new 



103 



