60. 



direct result of the environmental heterogeneity, in terms 

 of substrate variability, provided within canyons. This is 

 particularly true of canyons that have substantial exposures 

 of hard substrate and thus provide many sessile species with 

 suitable attachment sites. Canyons that do not have much 

 exposed outcrop tend to resemble slope environments and this 

 is reflected by their faunal constituents. 



In general, the shallow-water fauna (100-400 m) of 

 canyons does not differ markedly from that of the slope, with 

 the most common species being similar in both habitats. The 

 shallow water species also have narrower depth ranges in both 

 environments than do the deeper water ones. It is not known 

 whether this is due to competition, availability of suitable 

 substrate, temperature or barometric pressure tolerances. 

 There is a tendency for the slight emergence of some of these 

 species with increasing latitude. 



The greatest difference between slope and canyon habitats 

 is seen in the mid depth range (400-1100 m) . The slope tends 

 to be homogeneous with regard to substrate, while the canyons 

 offer a variety of different types. In determining the differ- 

 ence between the fauna found in the two environments, hard 

 substrate appears to be the most important. It provides 

 attachment sites for numerous sessile filter-feeding organisms, 

 and spatial heterogeneity for many small shrimp. The fauna of 

 the slope, on the other hand, is heavily dominated by the crab 



