The role of ontogenetic migrations in the formation of spatial 

 heterogeneity under the conditions of the Arctic ecosystem increases due 

 to the interruption (or decrease in the amplitude) of diurnal vertical 

 migrations during the polar day. It is the ontogenetic descent which 

 determines the replacement of the spring and summer oceanic complex of 

 species by the summer and fall neritic complex, changing the nature of the 

 plankton diet of the fish. In many cases, the ontogenetic migrations also 

 result in temporary intraspecies segregation. For example, in Calanus 

 glacial is in the fjords of Greenland (McLellan, 1957), the rise of VI 

 copepodites to the surface is synchronized with the phytoplankton peak in 

 the internal and external areas of the fjords, so that the stage I 

 copepodites are universally supplied with food. Therefore, the males with 

 spermatophores do not appear simultaneously in the various subpopulations. 



There are various means of achieving spatial separation. One of these 

 is the aggregation of distribution observed in any community. When there 

 is a '^ery high numerical strength of species, particularly in a glacial- 

 neritic system, clear effects of aggregation are observed. In the shallow 

 Arctic bays (e.g., in the Cheshskaya Bay of the Barents Sea), a multitude 

 of ephemeral "microcommunities" are observed. They are rather permanently 

 isolated from each other due to the shallow turbulent currents and complex 

 density stratification. Over a distance of a half mile, the plankton might 

 differ by 5 or 5 orders of magnitude as to number, as well as faunistic 

 composition. The number of crustaceans in accumulations might reach tens 

 of thousands of individuals per cubic meter (Zelickman, 1968a). 



However, the general trend in "demographic strategy" in the Arctic 

 ecosystem is survival through unfavorable conditions and awaiting more 

 favorable conditions, achieved in many ways. Survival adaptations include, 

 for example, latent stages of development in animals (N. M. Pertsova, 

 1974; Prygunkova, 1974; Zelickman, 1972) and the quiescent spores of algae; 

 the presence of the latter is one factor causing the first climax in the 

 development of phytoplankton to be observed in the shoals and air holes. 



Ecologic differentiation and "waiting strategies" dre also supported 

 by temperature regulation. During the vegetation season, the temperature 

 changes over broad limits, making the development of species of various 

 biogeographic and ecologic complexes possible. The differences in the 

 peaks in numbers are related to temperature as one of the background 

 mechanisms regulating the coexistence of the species. The temperature 

 determines the time of development of the eggs of the Copepoda (N. M. 

 Pertsova, 1974; McLaren, 1965; Corkett, McLaren, 1970; Corkett, 1972). 

 The larger the eggs, the longer their development. Considering the 

 differences in diameter of the eggs of the various species (£. f inmarchicus -- 

 145 pm, C. h elgolandicus --163 ym; C^. g lacial is --178 pm; C. hyperboreus -- 

 190 Mm), it becomes understandable that in zones where the areas of 

 distribution of these species overlap, the appearance of the young does 

 not occur at the same time and, consequently, the maximum in numbers is 

 not reached simultaneously. Furthermore, there is reason to believe 

 that the acclimation of females which survive the winter to low temperatures 

 facilitates more rapid development of their eggs (Landry, 1975) and, 

 consequently, separate utilization of the plant resources in the spring 



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