Figure 29. Sutured animal mounds, in 

 churned red clay, intermountain valley of 

 Rift Mountains, Indian Ocean. Depth: 

 1760 m. Photo area: 0.6 m x 4 m. 

 Type II camera. 2.4 m target distance. 

 The mounds are 5 cm high and probably 

 created or altered by crustaceans. 



debris is apt to be consumed by pelagic fishes before reach- 

 ing the sea floor. 



Benthonic organisms of the deep barren areas are 

 therefore forced to crawl, burrow, plow, hold fast, and 

 dig in the sediment for the minute quantities of food avail- 

 able (fig. 30). More churning, of course, takes place in 

 the organically rich, shallow coastal sediments (fig. 31), 

 because of the greater numbers and varieties of organisms 

 present. In the process of seeking food, the organisms 

 build undersurface galleries, tubes, and tunnels. 



Regardless of the total amount of churning, the 

 vertical height of the resulting microrelief seems to reach 

 an equilibrium at 6 centimeters above the sediment -water 

 interface. Benthonic organisms such as brittle stars, 

 holothurians, starfish, urchins, and even crustaceans 

 seem unable to build up larger microstructures and, indeed, 

 have no need to do so since their only objective is to obtain 

 food. 



48 



