A-4 



epifauna of a small submarine canyon (Alvin Canyon) was not 

 very distinct from that found on the adjacent slope. How- 

 ever, they do concede that several species may be considered 

 canyon indicators. Their conclusions on the similarity 

 between canyon and slope epifauna might not be indicative of 

 larger canyon systems. Alvin Canyon is rather small and, 

 therefore, may not provide as heterogeneous an environment 

 as the more deeply incised canyons. Additionally, trawls do 

 not adequately sample epifauna from regions of high relief 

 and rock outcrops such as are found in the larger canyons. 

 The investigators, however, did find higher population 

 densities in the canyons. This increased abundance again 

 substantiates the role of canyons in funneling nutrient 

 matter. 



The distribution of epifauna within canyons is largely 

 determined by the availability of substrate types (Hecker et 

 al., 1978). Thus an assessment of the density and distribu- 

 tion of fauna cannot be divorced from the geology of the 

 region. There is a distinct difference between the canyon 

 habitats found within our study area. The canyons off 

 Georges Bank are currently sites of active erosion (Ryan et 

 al., 1978), while the mid-Atlantic canyons are reported to 

 be largely inactive (B. C. Heezen, unpublished data; Keller 

 and Shepard, 1978) . An exception to this trend is Norfolk 

 Canyon which shows evidence of recent active erosion and 

 unusually high current velocities (E. B. Forde , personal 

 communication; Keller and Shepard, 1978). 



