NO. 5 BARNARD : AMPHIPODA 3 



THE CANYON ENVIRONMENT 



Physical 



Although turbidity currents are known to sweep down canyon axes 

 (Emery, Hiilsemann and Rodolfo, 1962; Johnson, 1964), and rather 

 continuous cascades of sand pour into canyon heads (Dill, 1962), the 

 lasting deleterious effects appear to be minor, as most canyon samples re- 

 ported upon herein and in Hartman (1963) contained significant animal 

 populations. However, none of the samples is known to have been taken 

 from an area of recent disturbance. Occasionally samples showed evi- 

 dence of impoverished faunas, but indicator species point to the presence 

 of outflowing fresh water from exposed aquifers (Hartman, 1963). A 

 great diversity of canyon sediments occurs even though canyon heads 

 entrap medium sands of shallow water. Emery and Hiilsemann's ( 1963) 

 data for canyons - 50 m above axes (plotted in Graph 1 as a scatter 

 diagram, and averaged in Table 1 ) show the great range in median par- 



zoo 



zoo 



300 



(/5 



0) 400 



c 



- 500 — 



O- 

 0) 



Q 



900 



TH \ \ \ \ r 



9-268 

 i-189 - 

 t-233 

 0966 

 ^144 



^216 . 

 ^435 



®-250 

 •-269 



9 ■ 9 9 



eoOr- 



700 — 



eoOr- : e 



e INSULAR 



10 20 30 40 50 60 70 80 90 100 120 140 



Median Diameter in Microns 



Graph 1. Scatter diagram of axial canyon sediments (0-50 m above 

 axes) in California. Plain dots represent inshore coastal canyons, 

 dots enclosed with circles represent insular canyons, l^ata from 

 Emery and Hiilsemann (1963). 



