although, in principle, there is doubtless a decrease in the abundance 

 of the crustaceans in feeding zones. 



The peculiarities of the biology of other Antarctic and, particularly, 

 Subantarctic euphausiids have been much less thoroughly studied. The 

 second most massive species is Thysanoessa macrura , widespread in the 

 Antarctic and extending into the southern Subantarctic. Judging from 

 the occurrence of the early stages, breeding of this species occurs 

 between October and February, the duration of the cycle being one year 

 (Ruud, 1932; Rustad, 1934; K. N. Pertsova, 1975). The population 

 maximum is found in the upper 100 meter layer. The regions of greatest 

 abundance of both mature individuals and larvae are extended along the 

 Antarctic convergence and divergence (Lomakina, 1964; K. N. Pertsova, 1975) 

 Euphausia triacantha has a similar distribution, but the primary con- 

 centrations of this species are clearly confined to the convergence zone 

 (Baker, 1959). This species performs great diurnal migrations, sub- 

 merging during the day to depths of over 250 m, and has a two-year cycle. 

 The duration of life of E_. frigida is the same. 



The third important group of herbivores is the salps. Of these, 

 the cycle of Sal pa thompsoni has been most thoroughly studied (Foxton, 

 1956). It is very common to the south of the Subtropical convergence. 

 The range of habitat extends down to 1500 m, the maximum population 

 being found in the surface water. There are daily migrations. During 

 the course of the winter, the juvenile asexual forms grow, developing 

 stolons which carry the buds of sexual zooids. Early in the spring, the 

 fully formed sections of the stolons begin to separate. From October 

 through February, their number increases by a factor of more than 10, but 

 then decreases once more in March. As the colonies grow, they submerge 

 into deeper water. In each, one fertilized egg develops which, after 

 completing morphogenesis, is liberated at the end of the summer and 

 continues to develop in the form of an individual, supplied with a food 

 reserve and already having a primordial stolon. The development of the 

 salps in the deep layers occurs more slowly and by the beginning of 

 spring, some individuals are still in the early stages of development. 

 Therefore, throughout the summer the population consists of organisms of 

 varying ages. 



The most numerous group of predators--the chaetognatha--is also 

 interzonal . Most abundant are Eukrohnia h amata , Sagitta gazellae and 

 S_. marri . The annual cycle is best known for S^. g azellae (David, 1955). 

 Breeding occurs in the deep zone from spring to fall. The region of its 

 greatest intensity shifts as the season progresses from the northern 

 Subantarctic to the south. The spawned eggs float into the upper 

 horizons: Hatching occurs at a depth of about 250 m, subsequent develop- 

 ment--in the 0-100 m layer. In the winter, the Sagitta grow by 

 approximately 5 mm per month, somewhat more rapidly in the spring and 

 summer. Juveniles, as they mature, gradually submerge, the more mature 

 individuals being located deeper. Mature individuals are found only at 

 depths of 1000-1500 m. The duration of one generation is one year. The 

 development of other species differs only in details. All species perform 

 seasonal migrations. 



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