The predaceous Hyperiidea Parathemlsto gaud1chaud1 begin to breed 

 in September. Each female spawns several times, after which some of the 

 females die, while others survive to the fall and breed again. The 

 juveniles appear in September, reaching their maximum number in December. 

 Due to the long period of breeding, the young crustaceans are present in 

 the plankton as late as June. Some of the larger females may survive 

 a second winter and breed again (Kane, 1966). 



A comparison of the mode of life of the most numerous plankters 

 shows great similarity with respect to the most important characteristics: 

 Breeding (or the time of its maximum intensity) in all species occurs in 

 the spring or summer; feeding and growth of the juveniles occur in the 

 Surface or subsurface layer; most of the population perform daily, 

 seasonal and/or ontogenetic vertical migrations, removing them from 

 the surface waters. 



This similarity of cycles in different groups of organisms is a 

 result of the peculiarities of the environmental conditions in the 

 Southern Ocean. The discontinuity of the process of primary production 

 makes it necessary for numerous species to spend the vegetation season in 

 the euphotic layer or directly beneath it. Here, the herbivores find 

 the maximum algae and can grow rapidly, breed and create reserves of 

 fat for the long winter, while the predators feed on the concentrations 

 of copepoda and euphausiid larvae. However, if the entire life cycle 

 were spent in the surface waters, there would be the danger of loss of 

 a significant portion of the population by being carried by meridional 

 Currents away from the breeding zone. Any vertical migration decreases 

 the effect of this transfer, while scattering into the deeper water 

 makes it harder for predators to decimate the population. The specifics 

 of the biotope have resulted in the predominance in the zoocene of the 

 cold-water pelagic zone of nonspecialized interzonal species, occupying 

 "large" niches in comparison to those of the tropical plankters. 



Another important feature of the life cycle of the zooplankters is 

 their great plasticity. This is manifested as the variable duration of 

 development of different individuals (P^. gaudichaudi , R. gigas , E^. 

 superba ) , as well as the mixed age composition of populations (S alpa 

 thompsoni , P_. gaudichaudi ) , and the variety of possible paths of 

 morphogenesis (E. superba" ). The plasticity of cycles allows the species, 

 depending on environmental changes, to change their development, which 

 serves as a sort of insurance in case of excessively severe perturbations. 



The differences between cycles consist in the greater length of the 

 breeding period of most predators in comparison with the existence of 

 high concentrations of their prey. The time of breeding and the range 

 of vertical distribution is also diverse in various species. At first 

 glance, these differences seem to be secondary in nature but, as will be 

 demonstrated below, they are of primary significance for the structure 

 and functioning of the community. 



The quantitative distribution of individual species is influenced 

 by a variety of factors, among which we can distinguish two important 

 groups: temporal and regional. The amplitude of fluctuations in the 



97 



