of the most characteristic planktonic organisms, but also the rare organisms, were carefully noted. 



The number or quantity of individual organisms was established by means of a Petri dish", 

 vrtiich was accepted as a standard. 



In cases where Calanus flnmarchicus or some other species of animals covered the entire 

 bottom of the Petri dish forming a single layer (this layer was carefully checked) we would assume 

 that there was a "fair" amount of organisms in the plankton. If only one half of the bottom of the 

 Petri dish was covered, it was looked upon as "little"; if only one-quarter, then it was regarded as 

 "very little". If, when checking the sample of plankton, it became necessary to divide or pour into 

 the Petri dish several times, then it was assumed that there was "much", "very much" or a "mass" 

 of plankton (depending on the number of checked portions: two, three, or more than three). The 

 volume of the deposit was also noted (for instance, 100 cm.). The nimiber of large organisms 

 (Hyperiidae, Euphausiacea, medusae jellyfish and Ctenophora) of the entire sample was counted. 

 At the same time, the entire plankton sample was weig^ied after it had been strained throu^ No. 

 23 gauze and dried on filter paper . The raw weight of plankton was then used to establish the con- 

 tents of 1 m^ (the plankton-tlter according to Yanshov JIT] ). In view of the fact that during the 

 spring- sirni me r period usually one species of organism predominates in the plankton samples 

 (rarely two or three), we regard this method as fully admissible for quick operative processing of 

 extensive planktonic material. Under field conditions and in a laboratory, one person can, by 

 means of this method, process about a thousand plankton samples in two to three months. 



Principles Governing the Seasonal Development of Plankton and Their Influence 



Upon the Distribution of Herring 



Extensive material on the composition and distribution of plankton obtained as a result of 

 Investigations in recent years has made it possible to establish the time of the beginning and of the 

 duration of biological seasons in the Norwegian and Greenland Seas (Figure 1). The principal forms 

 of plankton for every biological season were classified. Further, a chart of their distribution and 

 vertical shifts in the water strata was compiled. 



Figure 2 shows that the main mass of planktonic organisms winters in deep water; but, to- 

 wards the end of the hydrological winter, Calanus flnmarchicus and Euphauslidae rise in the water 

 and form pre-spawning concentrations near the surface. The spawning of crustaceans coincides 

 with the bloom of the alga Phaeocystis . These jAienomena mark the beginning of the biological 

 spring. Soon the "green bloom" (mass development of Phaeocystis) is replaced by a brown "diatom 

 bloom" . At this time, the young of Calanus grow into fat, red Calanus . EXiring the biological sum- 

 mer, the development of diatoms continues . Ctenophora and jellyfish appear and, together with 

 other planktophagous organisms, destroy the red Calanus . The crustaceans that survive descend 

 Into deep water. At the end of summer, when daylight is replaced by darkness, Calanus begins to 

 perform diurnal vertical migrations. Towards autimin, the vertical migrations by Calanus decrease. 

 Tiny Copepoda and thermofrfilllc organisms, as well as peridineans algae, appear in the surface 

 layers. With the onset of winter, the plankton concentrates in deep water. 



Experience has shown that when studying the seasonal phenomena in plankton. It is necess- 

 ary to bear in mind the likelihood of a shift in the times for the development of marine biological 

 processes under the influence of a decrease or Increase in the influx of warm waters from the 

 Atlantic. Further, one must bear in mind the warming of the 'water due to solar radiation, the 

 chilling of the waters due to melting ice, etc. 



1/ A Petri dish has a diameter of 10 cm. 



107 



