3. C ommunities of the Temperate Waters of the Northern Hemisphere 

 Is. A. Mileikovsky, L. A. Ponomareva, T. N. Semenova) 



3.1 . Some Biological Peculiarities of Planktonic Communities in 

 the Co1d-Temperate Regions of the Northern Hemisphere 



V. G. Bogorov (1941, 1974) worked out a scheme of biologic seasonal 

 cycle in the plankton of the temperate waters of the northern hemisphere, 

 describing its annual cycle as bicyclic with four phenologic (biologic) 

 seasons. During biologic winter, the annual minimum of plankton occurs 

 with predominance of zooplankton over phytoplankton. The biologic spring 

 is the time of the annual maximum of plankton biomass, with significant 

 predominance of phytoplankton. In the summer, the zooplankton reaches its 

 maximum, while the total biomass of plankton decreases, and the biomass of 

 phytoplankton becomes equal to or less than the biomass of zooplankton. At 

 the end of the summer and in the fall, a second, smaller maximum of phyto- 

 plankton develops, and at the end of the fall it begins to decrease, leading 

 to the winter minimum. During the course of the annual cycle, the develop- 

 ment of phytoplankton precedes that of zooplankton, the difference 

 between the maxima and minima of phytoplankton being greater than is the 

 case for the zooplankton. 



The scheme of V. G. Bogorov, however, was constructed practically 

 completely on materials observed in the North Atlantic. A. K. Heinrich 

 (1961a) developed the scheme further and made it much more specific by 

 considering the extensive material available concerning the North Pacific. 

 She showed that the annual cycles of the various species of zooplankton are 

 too different to allow any biologic season in the plankton to be described only 

 by specific age composition of the whole zooplankton. Similarly, we cannot 

 find identical characteristics of analogous seasons in terms of the relation- 

 ship between the quantities of phytoplankton and zooplankton for all regions 

 in the temperate latitudes. Therefore, the characteristics suggested by 

 V. G. Bogorov (1941) are not applicable to the temperate latitudes as a 

 whole. 



In the opinion of A. K. Geinrich, as we attempt to differentiate 

 the biologic seasons in the marine plankton, we must base our discussion 

 on different characteristics from those used by V. G. Bogorov. The annual 

 cycle can be divided into natural segments, each of which is characterized 

 by a definite group of seasonal species present in the plankton only during 

 this time segment, and a definite stage in the life cycle (annual maximum) 

 of year-round species. However, due to the gradual nature of replacement of 

 one group of species by another, any seasonal boundaries we select are 

 arbitrary to some extent. The clearest boundary between seasons in the 

 cold-temperate regions is the boundary between winter and spring, which 

 marks the beginning of the vegetation of the phytoplankton. 



In the zooplankton of the cold-temperate regions of the northern 

 hemisphere, a very important role is played by a few common genera of 



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