68 



The Substratum 



examples of the control of bottom fauna and flora by the substratum 

 in coastal water are given by Yonge (1949) and by Pratt (1953), and 

 in fresh water by Krecker and Lancaster (1933) and by Wilson 

 (1939). 



Farther offshore conditions cannot be so easily observed, but the 

 modern quantitative dredge and the underwater camera have shown 

 that the same selective action is being exerted by the nature of the 

 bottom material. Samples dredged from mud and from coarse shell- 

 gravel at locations only a few miles apart in the English Channel were 

 shown by Wilson ( 1951 ) to contain strikingly different animal types. 

 Such differences influence fish populations feeding upon these ben- 

 thonic species. Studies made with the underwater camera have the 

 advantage that they reveal the nature of the bottom material and the 

 organisms living on it in their undisturbed condition. The dimen- 

 sions of bottom features such as ripples, and the spatial distribution of 

 the inhabitants may then be examined quantitatively (Fig. 3.4). In 

 the abyssobenthic zone of the ocean the bottom material usually con- 

 sists of a soft mud, and here only those animals with long legs, broad 

 bases, or other special adaptation can move about without being 

 smothered. At a depth of 1% miles the candid underwater camera 

 caught a 60-cm "sea cucumber" as it cruised across the muddy bottom 







Photo made with Eicing undersea camera by J. F.unii;, H'uads Hole Oceanographic Institution 



Fig. 3.5. A holothurian ( "sea ciK;umber" ) moving over the mud at a depth of 



2600 m {\Yj, miles) on the floor of the open oeean ofl:' the coast of New York. 



Note the imprint of the double row of tube feet. 



