A-11. 



sediment. Study of photographs would then tend to overesti- 

 mate the abundance of these species. This was compensated 

 for by not counting individuals that were seen in successive 

 frames. Other organisms, such as the large crab Geryon 

 quinquidens and various fish, obviously try to avoid the path 

 of the submersible. Nothing could be done to alleviate this 

 bias, because it is impossible to determine what organism has 

 caused a dust cloud seen in a photograph. Another bias which 

 could not be compensated for is that the habitat of some 

 organisms, such as burrowers or ones that hide beneath rocks, 

 precludes an accurate assessment of their abundances because 

 they are rarely out on the substrate and thus are not seen on 

 the photographs. 



Statistical Techniques 



The species, their abundance and the m viewed were 

 summed for 50 meter depth intervals for each dive. This data 

 was then standardized by calculating the number of indivi- 

 duals per 100 m^ , for each species and for the total fauna. 

 The relative percent that each species contributed to the 

 total fauna seen was also calculated for each depth interval. 

 Percentage faunal similarity was calculated between 50 meter 

 depth intervals within a dive and for similar depth intervals 

 between dives. The index used was percentage similarity 

 (Whittaker and Fairbanks, 1958) given by the formula 



