Table 1. Change in significance of basic trophic groups of mesoplankton 

 in Kuril region of the Pacific Ocean with depth in the summer of 1966 

 (% of total mass of mesoplankton in each level, ignoring interzonal filter 

 feeders which do not feed at the depth where caught--after Vinogradov, 1968). 



Depth, m 



Filter feeders 



(phytophages 

 and detrito- 

 phages) 



0-50 



50-100 



100-200 



200-300 



300-500 



500-750 



750-1000 



1000-1500 



1500-2000 



2000-2500 



2500-3000 



3000-4000 



4000-5000 



5000-6000 



6000-7000 



>7000 



83 



57 



40 



53 



50 



9 



11 



4 



2 



3 



5 



3 



3 



1 



1 



4 



*The biomass of predators is low, since we do not include the weight 

 of coelenterates or of large cephalopods and fish which are not easily caught 



in plankton nets, 



place, being able to utilize the greatest variety of food--living organisms, 

 their remains and fecal matter, raining down from the overlying layers. 



At 4000-6000 m depth, the significance of phytophages increases again, 

 due to the presence of mysids of the genus Boreomysis . These mysids feed 

 on phytoplankton in the surface layers, then descend to the deeper layers, 

 where there are practically no predators, and the probability of their 

 being eaten is greatly reduced. Studies performed on board the VITYAZ 

 have shown that groups of Boreomysis incisa with stomachs packed with 

 fragments of diatoms and Tintinoidea, are constantly observed at a depth 

 of 4000-6000 m, sometimes slightly higher or lower (Vinogradov, 1970a). 

 This indicates that there is regular, rapid transport of phytoplankton 

 through a tremendous mass of water and emphasizes once more the importance 

 of vertical migration in the transportation of organic matter from the 

 productive zone to the depths of the ocean. Almost the entire mass of 

 copepods at these depths consists of euryphages. Deeper than 6000 m, the 



44 



