commercial fish, such as young redfish (Konchina, 1968). The same is true 

 of Heterorhabdus n orvegicus , although this copepod is not numerous and its 

 role in the plankton is much more modest. Not being related to the period 

 of vegetation of the phytoplankton, the predaceous copepods breed year- 

 round and may be greatest in number when the phytophages are at their 

 period of minimal development, for example, during the fall and winter 

 season, as is observed for P_. n orvegica in the Norwegian Sea. 



The Cyclopoida are represented in the plankton of the boreal Atlantic 

 primarily by species of the families Oithonidae and Oncaeidae, which 

 include some abundant species: the cosmopolitan Oithona similis , the 

 Arctic-boreal Oncaea boreal is and the boreal Oithona atlantica and Oncaea 

 coni fera . The population of 0. simil is is relatively large throughout the 

 year, forming a sort of background against which the peaks of development 

 of the other plentiful species of copepods appear in sequence. In winter, 

 when the number of other copepods decreases, 0^. simil is moves to first 

 place, composing 60-70% of the total number of zooplankton. In contrast to 

 it, 0_. boreal is has its peak in number in late spring and early summer. 

 During this period in the Norwegian Sea it may amount to 10-30% of the 

 total zooplankton population; this is significant, recalling that in this 

 season the total number of planktonic animals is generally quite high 

 (Gruzov, 1963). Approximately the same relationships are characteristic 

 for these species in the Labrador Basin (Pavshtiks, 1966). In the open 

 waters of the boreal Atlantic, the significance of 0^. atlantica and 0. 

 coni fera , which are not numerous in the northern portion of the boreal 

 aresy increases. 



The next group after the copepods, quite important in the creation of 

 high biomasses of zooplankton in the boreal Atlantic, is the Euphausiacea . 

 Of these, most numerous are Thysanoessa longicaudata and Meganyctiphanes 

 norvegica- -borea1 oceanic species. Th. longicaudata forms accumulations 

 primarily in the surface zone. M. norvegica is less numerous and is 

 encountered primarily at depths of 200-500 m, though it frequently rises to 

 the surface. Both species are euryphagous, feeding primarily on detritus 

 and phytoplankton (Mauchline, Fisher, 1969); therefore, their life cycle 

 is related to the period of vegetation of the planktonic algae. The 

 reproductive season of Th. l ongicaudata in the Labrador Basin extends from 

 May through September, with the greatest number observed in July- 

 August, while in winter only mature individuals are seen (Kielhorn, 1952). 

 In waters of Atlantic origin in the Norwegian Sea, the greatest biomass 

 of euphausiids is seen in May and June (Gruzov, 1963; Timokhina, 1968). 



Among the boreal hyperiid amphipods, Parathemisto abyssorum is most 

 important in the North Atlantic. Juvenile Parathemisto are seen in the 

 largest numbers in spring and early summer. 



The groups of planktonic crustaceans which we have considered: copepods, 

 euphausiids and hyperiids, are determinant in the formation of the food 

 Supply for commercial planktophagous fish. In addition to them, the active 

 planktonic predators are quite significant in the Atlantic boreal communities: 



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