NO. 5 BARNARD: AMPHIPODA 21 



yal Nicippe tumida is a member of the fauna. Several other cold-water 

 sublittoral species, such as Paraphoxus oculatus, Leptophoxus falcatus, 

 Ampelisca eoa and Sophrosyne robertsoni are present also, these species 

 not being found in the warm-temperate sublittoral of southern Califor- 

 nia. Pardaliscella symmetrica, an upper slope species, is found in San 

 Nicolas Basin. 



The remaining deeper basins have less biotic diversity but also sup- 

 port Heterophoxus oculatus. San Clemente Basin has a member of Lepi- 

 depecreella, heretofore considered a littoral cold-water genus, and 

 strangely enough, Phoxocephalus homilis, a deep sublittoral warm-tem- 

 perate species, has been found there. 



More intensive sampling, no doubt, will reveal additional deep sub- 

 littoral species that stray into the basins, but these should be offset by an 

 increased recovery of rare (low frequencies of individuals), optimally 

 bathyal species. The straying of sublittoral and shallow bathyal taxa into 

 the basins probably would not occur were the basins located far offshore. 



THE AMPHIPODA 



Frequency of Amphipoda in Basin and Canyons 



The frequency of Amphipoda in the shallow-water canyon heads is 

 scarcely less than that on the coastal shelf (compare densities at 100 m 

 for shelf and canyon in Table 10), perhaps indicating the unstable sub- 

 stratum, but also perhaps denoting errors because of the difficulty of ob- 

 taining samples in canyons. The grabbing device may hit steep slopes in 

 the narrow canyon heads during or after sampling and small crusta- 

 ceans may be lost in the recovery. Fast-moving demersal species may 

 sense and escape the descending grab. The substratum in the shallow 

 heads is sandy and the density of organisms is known to decrease on 

 sandy bottoms, as shown by Barnard ( 1963), although the figure of 257 

 individuals/m^ in the inshore sands in depths of less than 10 m is roughly 

 half that in the canyon heads on substrata in less than 100 m of depth. 



The frequency of Amphipoda declines erratically with depth in the 

 canyons, indicating the need for consideration of many more samples to 

 eliminate not only sampling error, but to equate the variations of sedi- 

 ments and other environmental factors. Nevertheless, four provinces of 

 density appear in the data in these depths: (1) between and 100 m, 

 where the average density is 588 individuals/m^, (2) between 101 and 

 500 m, where the density is 54/m-, (3) between 501 and 1000 m, 

 where the density is 14.7 individuals/m^, and (4) between 1001 and. 

 1600 m, where the density is 2.8 individuals/m-. 



