164 



Life 



SAN NICOLAS 



BASIN 



2083 2087 



SANTA 

 C ATA LIN A BASIN 

 2111 2099 2100 I999g 



SAN PEDRO BASIN 

 2096 2101 2097 2108 2102 2105 



I200r 



Figure 141. Distribution by basin and depth of batiiypelagic coelenterates in photographs. Bars show numbers of 

 individuals at 30-meter depth intervals above the bottom. 



as an annual crop for many years (Wohnus, 

 1942). In spite of their fragileness, pieces 

 of kelp are occasionally found as fossils 

 (Fig. 143). 



In addition to the large kelps, many 

 smaller algae occur mostly on the inner 

 halves of the shelves. Some are collected 

 for agar by diving (Tseng, 1944, 1946), and 

 all serve as a food source and protective 

 cover to many kinds of animals which live 

 on and among them. On bank tops and on 

 some island shelves, such as part of that 

 around Santa Barbara Island, calcareous 

 algae in the form of balls or granules of cal- 

 cium carbonate may be the chief constituent 

 of the local sediment. 



The animals of the shelves, unlike those 

 of the intertidal area, exhibit little zonation 

 by simple depth except in depths of only a 

 few tens of meters. Instead, the chief con- 

 trol appears to be that of bottom material, 

 important factors being grain size and con- 

 tent of organic matter. As discussed in the 

 later section on sediments, these and other 

 characteristics of sediment on shelves usually 

 vary sharply, giving rise to a patchy distri- 

 bution of sediments on such youthful shelves 



as those of southern California. As a result, 

 the animals living on them are variable and 

 patchy in both numbers and kinds. To give 

 a fully detailed description of the animals is 

 impossible at present; however, work com- 

 pleted to date by Hartman {\955b, 1956) and 

 Hartman and Barnard (1957) plus much 

 unpublished material permit the making of 

 some general statements about the faunas 

 of the shelves. 



The biomass of the mainland shelf is 

 highly variable, 40 to 4000 grams of living 

 organisms (with shells) per square meter of 

 area, but it averages about 300, a figure that 

 represents a high concentration of life. 

 Greatest biomasses occur in areas of fine 

 sediment and also near sources of sewage 

 pollution. For individual orange peel bucket 

 samples having effective sampling areas be- 

 tween 0.10 and 0.25 sq meters, the number 

 of species averages about 70 and the number 

 of individual specimens about 420. Thus 

 the bioindex, or number of individuals per 

 species, averages 6.0, although it ranges be- 

 tween 3.5 and 22.9. West of Santa Barbara 

 the fauna has a northern aspect owing to the 

 cold water of this area as well as to prox- 



