Microrelief Caused by the Bodies of 

 Benthonic Organisms 



That organisms exist on the sea floor has, of course, 

 been known for many years. 33 " 35 Strange looking creatures 

 have been brought to the surface by dredge, trawl, sound- 

 ing leads, nets, anchors, scoops, and other means in 

 increasing numbers (figs. 22 through 27). Although many 

 of these animals are alike in structure, they differ from 

 species that live in shallow environments. 



Because of the usual haphazard manner of collec- 

 tion and lack of detailed distribution information, little is 

 known about these bottom feeders and burrowers. Sampling 

 has been insufficient to establish the concentration of most 

 of them. Exact identification from photographs, also, is 

 difficult unless actual specimens are available for confirma- 

 tion. However, increased use of bottom photography and 

 coordinated sampling has somewhat alleviated these diffi- 

 culties, and the concentration of a few identifiable animals 

 has been obtained. ^ 



Few underwater photos of the sea floor exceed 5 

 square meters in coverage. Most present-day samplers 

 collect from areas of about 0. 4 to 1 square meter of the 

 sea floor. And single grabs seldom bring up more than 

 one organism or part of an organism, although bottom 

 trawls and dredges screen more sediment and yield more 

 specimens. 35 Thus, few of the deep-sea animals are ever 

 visible for counting and examination. And counting is 

 complicated by the fact that some organisms combine 

 bottom and subbottom feeding habits. 



In most deep-sea environments the food supply is 

 sufficient to support only a few animals, from less than one 

 per square meter in fine-grained red clays to approximately 

 ten in richer near shore silts and clays. In abyssal plains 

 and interseamount areas where intermediate relief is slight, 

 the numbers are even smaller. Those animals living at 

 the interface and visible in photographs vary in size from 

 less than a millimeter to 15 centimeters in length (fig. 28). 



To constitute effective microrelief on the sea floor, 

 many organisms would have to be concentrated there. In 

 large enough numbers, as in shallow water, crustaceans, 



44 



