224 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 22 



shore ; and secondly, the basins are enclosed by sills that alter the bottom 

 water movements and oxygen supplies. We are unable to balance these 

 opposing forces in terms of a trend, for we have no comparative data. 

 On the basis of lowered oxygen values, some basins should have fewer 

 species than similar depths with higher oxygen ; on the basis of distance 

 from shore and depth, the inshore basins should have a higher food 

 supply and more numerous species than deeper offshore basins. It would 

 appear that oxygen is the more critical limiting factor, since the three 

 shallower basins with higher food supply have in two cases far fewer 

 species than almost all other deeper basins; and in the case of the much 

 better sampled San Pedro Basin with its 115 species, only slightly 

 fewer than the poorly sampled Santa Catalina Basin with 119 species 

 (Table 1). 



It is puzzling that Santa Monica Basin has less than 20% as many 

 species as the San Pedro Basin, yet they have nearly the same bottom 

 and sill depths and oxygen supplies. One factor is that many more 

 samples have been taken in San Pedro Basin, but another factor may 

 be that San Pedro Basin lies closer to shore than Santa Monica Basin, 

 so that shelf species are able to settle easier. Thus, we conceive of larvae 

 being carried down into the supply waters of the basins from shallower 

 areas, either by sedimentation or by currents. Many of these species 

 may be able to survive vegetatively after settling, but a continuance of 

 the species occupying the bottoms depends on fresh supplies. San Pedro 

 Basin is closer to shore and may be in a more favorable position from 

 the hydrographic standpoint for a higher supply of such vegetative 

 species. Emery (1954) shows that the water source for Santa Monica 

 Basin trends north from the San Pedro Basin; these waters, once over 

 San Pedro Basin, may be deficient in shallow water larvae. In Table 

 3 we see that Santa Monica Basin has the highest percentage of shelf 

 species composing its fauna, 73% compared with 63% in San Pedro 

 Basin ; but Santa Monica Basin has only 1 1 species of which eight are 

 shelf, while San Pedro Basin fauna has 176 species of which 48 are 

 shelf. 



Greater distance from shore and greater depth are most comparable 

 in Santa Catalina and San Nicolas Basins, each with 1 1 samples. Santa 

 Catalina is the shallower and closer to shore, with 119 species, while 

 San Nicolas has 90 species. In this same regard it is unfortunate that 

 Santa Cruz and Long Basins cannot be compared ; but the samples from 

 Santa Cruz were not perfect in their collection. 



