starfish, brittle stars, sea cucumbers, sponges, crinoids, 

 worms, and urchins might have sufficient density and height 

 to constitute microstructures capable of reflecting sound 

 or changing coefficients of sound reflection. 



It may be concluded that, except in shallow areas, 

 the bodies of living organisms themselves hardly affect 

 the reflection of sound. 



Microrelief Caused by the Activity of 

 Benthonic Organisms 



During feeding, benthonic organisms churn up the 

 softer sediments of the sea floor. 11,:L3 Sokolova, working 

 in the Kurile -Kamchatka Trench of the Pacific Ocean, 

 found that most (about 55 percent) of deep-sea bottom invert- 

 ebrates are deposit feeders, a smaller number (about 25 

 percent) are suspension feeders, and still fewer (about 20 

 percent) are carnivorous. 36 Further, the composition and 

 quantitative abundance of deep-sea communities are largely 

 determined by the amount of organic material on the sea 

 floor and in suspension in the water layers just above the 

 bottom. Sokolova adds that a zonation of communities 

 arises, each zone extending over a region characterized 

 by a distinct type of sedimentation. The dominant organisms 

 in each area are those best adapted to it by their feeding 

 habits. 



Organisms living in the deep-sea environment must 

 spend their entire lives seeking out and digesting food. Even 

 where food is plentiful, for example, in nearshore areas 

 fed by rich subaerial runoff, the organisms must spend 

 most of their time seeking food. 



Laughton 1 found more sediment disturbance and 

 more animals in shallow water (fig. 26), and less disturbance 

 and fewer animals in deep water (fig. 28). This relation- 

 ship results from diminishing food supplies with increasing 

 depth. Numerous bottom photographs on deep abyssal 

 plains bear this out (fig. 29); here the main source of food 

 is the surface water. If the latter is not rich in nutrients, 

 as it seldom seems to be over abyssal areas of the midlati- 

 tudes, very little organic debris falls to the sea floor. Also, 

 because of the great depth, a large percentage of the falling 



47 



