phytophagous copepods; Calanus , Pseudocalanus , Metridia , etc. Among the 

 holoplanktonic phytophagous forms, three types of life cycles can be 

 distinguished (Heinrich, 1961a). The first type includes species in which 

 breeding of the first generation is related to the spring development of 

 phytoplankton and cannot begin any earlier. This type of life cycle is 

 exhibited by C alanus finmarchicus , dominant in planktonic communities of 

 the temperate waters of the North Atlantic (Marshall, Orr, 1955; Bogorov, 

 1941), as a result of which the annual maximum zooplankton biomass follows 

 the spring pulse of phytoplankton. A modification of this type is the life 

 cycle in which breeding and growth can occur only when phytoplankton is 

 sufficiently abundant; the transition from the last copepodite stage to 

 the adult occurring at the beginning of the period of phytoplankton vegeta- 

 tion. In regions of domination of these species (e.g., Eucalanus bungii in the 

 Bering Sea and northwestern Pacific), the annual maximum of zooplankton 

 biomass is seen in the spring (Heinrich, 1957, 1961a). 



The second type of life cycle is exhibited by forms, the breeding of 

 which is independent of the quantity of phytoplankton and may occur either 

 in spring, or in other seasons: C alanus cristatus and C^. plumchrus in the 

 North Pacific, Metridia longa and C^. hyperboreus in the North Atlantic. 

 Species with life cycles of the first and second types usually have 1-3 

 generations per year in the cold-temperate regions. 



The third type of life cycle is that of species which can multiply 

 throughout the year, but do so most rapidly during the period of vegetation 

 of the phytoplankton. Most of the smaller forms of copepods fall into 

 this group, and have several generations per year. 



A. K. Heinrich (1961a) also reports that the presence in the plankton 

 of the cold-temperate regions of certain neritic species of Cladocera and 

 Copepoda is always a characteristic of the summer and early fall. 



The breeding of predaceous copepods, for example, Pareuchaeta spp., in 

 the opinion of A. K. Heinrich, is independent of the phytoplankton and is 

 not limited by the presence of animal food, which is always sufficient; 

 these species breed throughout the year. However, the abundance of phyto- 

 plankton does determine the success of the breeding of phytophagous 

 zooplankton and, therefore, the food base available for the predators. Data 

 on common pelagic polychaetes, the pteropod mollusk C lione limacina and 

 chaetognaths (Kaufman, 1967; Mileikovsky, 1962, 1969", 1970; Dunbar, 1962) 

 indicate that seasonal breeding is a common phenomenon among predatory 

 holoplankters of the cold-temperate communities. 



Among the widespread, common species, the peculiarities of the life 

 cycle change with latitude and may differ in the southern and northern 

 portions of their ranges. The number of generat"'ons during one reproductive 

 season, in particular, differs with latitude: The further north, the fewer 

 the number of generations. 



In the cold-temperate zone, the nature of the sequence in maxima of 

 biomass of phytoplankton and zooplankton is determined by the type of life 



66 



