150-Meter Stations 



One of the two 150-m stations in Lydonia Canyon was sampled four times 

 and then relocated, because at the first site we were sampling the wall of the 

 canyon where sediments were highly variable. In general, sediments at this 

 first site were very coarse, with less than 1 percent silt-plus-clay. At the 

 new station location where sediments were finer, the average silt-plus-clay 

 was about 30 percent. The slope station outside the canyon had fine sandy 

 sediments, with about 2 percent silt-plus-clay. 



Faunal Composition and Dominance 



Species composition was strikingly different between the two canyon 

 stations. Of the top 20 numerically dominant species, 8 were shared between 

 the two stations, but none of the top 10 dominants at one station were among 

 the top 10 at the other. 



The dominant species at the coarse-sediment canyon station was a 

 polychaete, Lumbrineris /atre/Z/i, which accounted for 7 percent of the fauna. 

 The rank of several of the subdominants at the coarse-sediment station varied 

 widely over the four sampling dates, probably because the same sediment type 

 was not sampled each time. 



At the fine-sediment canyon station, the top dominant was the amphipod 



Ampelisca agassi'zi, which accounted for about 12 percent of all individuals. 



This species consistently ranked either first or second, except once when it 

 ranked fourth. 



At the adjacent slope station, this same amphipod was the top dominant on 

 each of 12 sampling dates. Here, however, Ampelisca accounted for 35 percent 

 of all individuals. Comparing dominants between the canyon stations and the 

 slope station, there were more in common between the coarse-sediment station 

 and the slope station than between the fine-sediment canyon station and the 

 slope station. Of the top 20 dominants at the coarse-sediment canyon station, 



68 



