188 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 19 



ing infaunal polychaetes, nemerteans, enteropneusts, and some others. 

 They maintain a dynamic stability, showing no seasonal differences, and 

 have continued to flourish through several years. 



This broadly oval submarine area was marked off as a grid, at about 

 two-mile intervals, resulting in 267 intersecting points (Hartman, 1955, 

 pp. 6, 7). Grab samples were taken from these pre-selected sites, and 

 analyzed for their specific components. The samples varied greatly in 

 volumetric sizes, ranging from 0.06 to nearly 3 cubic feet. The surface 

 areas covered by the sampler probably varied far less, because the initial 

 bite-size was more nearly equal for all samples. The sampler was effec- 

 tive in taking surface scratchings, where the largest numbers of animals 

 are known to occur. In assessing unit quantitative values, therefore, not 

 only differences in grab sizes, but kinds of substrata are to be considered. 

 It is further noteworthy that all final values must be considered minimal, 

 for only those organisms which finally reached the microscope and the 

 specialist could be fully named and recorded. In this study, therefore, it 

 would be meaningless to re-assess these areal quantities to units of a 

 square meter, for it has been observed repeatedly that the aggregates of 

 animals in the San Pedro area occur in small patches, with surface units 

 perhaps much less than a square meter. Even more importantly, it has 

 been shown that the faunal units are patchy, differing greatly from one 

 sample to the next. 



Except for differences in contour, the physical features are fairly 

 uniform. Salinity is nearly constant throughout the year, ranging from 

 33.5% near the surface (physical data are from Emery, 1960, p. 108) 

 to 34.29% in 100 fms. There is some indication that lowered salinities 

 occur in scattered spots, possibly near aquifers, as indicated by the pres- 

 ence of peak numbers of the polychaete Capitella capitata subspp. Such 

 spots have been found in the San Pedro shelf as well as in other offshore 

 places (Hartman, 1961a). Temperatures in the sediments vary little, 

 from 12.5°C near the surface, to 8.5°C in 100 fms, and 5.06°C in 495 

 fms, in the San Pedro basin. Dissolved oxygen varies from 5.5 ml/1 at 

 50 fms, 1.5 ml/1 at 100 fms, to only 0.2 ml/1 in the San Pedro basin, 

 where there is almost no life. Sediments are chiefly sands, with coarser 

 fractions near beaches and increasingly finer sands at greater distances 

 from shore ; sands change to silty sands, sandy silts and then to clays and 

 oozes along deep slopes, in canyon and basin depths, and axes of canyons, 

 and their lower ends may have coarse gravels (Emery and Hiilsemann, 

 1963, p. 62). Some rocky outcrops, such as the sea mounts, are conspicu- 

 ous in a few places. Red sands, near Alamitos Bay, in 3 to 7.5 fms, and 

 near the center of San Pedro shelf, are sparse. 



