GENERAL CHARACTERISTICS OF FAR EASTERN SEAS 721 



Table 293. Number of species of pelagic Gam- 

 mar idae at different depths of Kuril- Kamchatka 

 trench ( Ya. Bir stein and M. Vinogradov, J 955). 

 The zones correspond to those in Fig. 338 



No. of 

 Zones and sub-zones species 



Surface 1 



Transitional 1 



Upper abyssal 1 3 



Lower abyssal 1 2 



Ultra-abyssal 6 



Quantitative development of different groups varies greatly with the horizon 

 (Eig. 348). While Porifera (Hondrocladia, Hyalonema) are predominant at a 

 depth of 1 ,000 to 2,000 m, holothurians (Elpiidae) and starfish (Porcellana- 

 steridae) are the main groups between 2,500 and 7,000 m; still farther down 

 holothurians become predominant in terms of biomass. At times the number 

 of Pogonophorae specimens is remarkable. Thus, for example, about 3,000 

 specimens of Elpiidae, more than 4,000 tubes of Pogonophorae, mainly 

 Zenkevitchiana, and about 100 specimens of Echiuroidea vitjazema were 

 brought up from a depth of 9,000 m in one sweep at one of the stations in the 

 Kuril-Kamchatka trench. 



The qualitative variety of plankton increases with depth, while its numbers 

 decrease steadily {Table 294) by no less than 1 ,000 times from the surface to the 

 great oceanic depths ; and probably, if we include the coastal areas and the 

 periods of the greatest development of surface plankton, by several thousand 

 times. 



An interesting comparison of the vertical distribution of plankton biomass 

 in the Kuril-Kamchatka, Mariana and Bougainville trenches is given by 

 M. Vinogradov (1958) {Table 294). 



Table 294. Vertical distribution of plankton biomass {mgjm 3 ) 



Benthos biomass fluctuations from the surface to great depths are even 

 more marked. Even within the limits of the abyssal the benthos biomass may 

 vary by some hundreds of times {Table 295). 



2z 



