The number of eggs produced by the females is apparently directly dependent 

 on their food supply, i.e., on the Quantity of algae present during the 

 spawning season. The buoyancy of the eggs of the copepods is negative, 

 but some excretions of the phytoplankton increase the viscosity of the 

 water and slow the sinking of the eggs (Maloney, Tressler, 1942). The 

 nauplii emerge in the uppermost layers of water and a high concentration 

 of the population, the core of which is usually in the upper portion of 

 the mixing layer, is characteristic for early stages of the development 

 of the generations. The total number of individuals reaches its maximum 

 during this period. Later, as the crustaceans grow, they gradually 

 disperse vertically: The older stages begin to sink into the depths, 

 and at first the lower boundary, then the upper boundary of their habitat 

 move downward. Therefore, in the summer the cores of abundance of 

 individual copepodite stages typically go deeper as they become older 

 (Voronina, 1970a, 1974). 



As time passes, the populations are significantly reduced in number, 

 but, due to the intensive growth of the individuals, their total biomass 

 increases, reaching its maximum in the surface layer during the period 

 of dominance of the fourth and fifth copepodite stages. Older stages, 

 having accumulated large droplets of fat, begin to leave the euphotic 

 zone and disperse through the mass of the water. The number maxima of 

 the individual species are observed in the winter at a depth of 750-1000 

 or 250-750 m (Mackintosh, 1937: Andrews, 1966). The wintering populations 

 of copepods over most of the aquatorium are characterized by predominance 

 of the fourth and fifth copepodite stages. During this period, the 

 crustaceans do not feed and utilize the summer fat reserves. The popula- 

 tions retain the seouence of individual copepodite stages along the 

 vertical of late summer: younger copepodites are located higher than 

 older. However, in spring, as the rise begins, a restructuring of the 

 vertical distribution occurs, since the mature individuals which move more 

 rapidly than the others, catch up with and even pass first and fifth, then 

 the fourth stage copepodites, after which the fifth stage copepodites pass 

 the fourth stage copepodites. As a result, a structure is produced which 

 is typical for the final stages of migration, in which the older stages 

 are followed by younger stages from the top downward. The vertical spread 

 is greatly reduced, reaching its minimum during the spawning period. In 

 general features, the changes in the sequence of copepodite stages along 

 the vertical and of quantitative distribution of species numbers by 

 depth can be represented as in the diagrams below (Figs. 14 and 15). The 

 individual stages of this cycle differ in their age composition and total 

 numbers of populations. 



This type of restructuring has been seen for Calanus p ropinquus , C. 

 s imil 1 imus , Calanoides acutus , Rhincalanus gigas , as well as Pareuchaeta 

 antarctica and Metridia gerlachei , in which it is somewhat complicated 

 by the daily vertical migrations. Apparently, these cycles are charac- 

 teristic of all interzonal copepods which breed in the surface layer. 



One important peculiarity of the annual cycles of planktonic animals 

 is the asynchronism in occurrence of identical stages of these cycles in 

 various latitudinal zones. The rise to the surface, breeding, attainment 



90 



