166 



Life 



Figure 143. Fossil brown alga collected by C. L. Hubbs 

 and E. Y. Dawson from Late Miocene Capistrano for- 

 mation 1 km south of Capistrano Beach Pier. The slight 

 discoloration around the algal blades is from coating of 

 collodion preservative (xO.7). 



moUusks comprise most of the rest of the 

 numbers of species and individuals. Be- 

 cause of their small size, the numerous crus- 

 taceans form only a small percentage of the 

 total biomass, in contrast to the larger but 

 less numerous echinoderms. In a general 

 way the fauna of soft muddy areas of the 

 shelf where unaltered by pollution consists 

 of many species of polychaetes with no 

 dominant one, of Paraphoxus sp. and sev- 

 eral other amphipods, of urchins including 

 Lytechinus anamesus, and of few species liv- 

 ing atop the sediments. At the outer edge 

 of the shelf and in other areas of sandy 

 bottom, the biomass is low, and there are 

 few animals other than smooth red ophiu- 

 roids, which may be abundant (Fig. 145). 

 The ophiuroids and most other animals here 



live at the surface of the sediment. Where 

 the bottom is rocky, the fauna is dominated 

 by sessile organisms such as sponges, bryo- 

 zoans, hydroids, alcyonarians, tunicates, and 

 barnacles. Areas of high sewage pollution 

 such as the shelf off Palos Verdes Hills have 

 an abundance of the tube worm, Chaetop- 

 terus variopedatus, living atop the sediment 

 and frequently in association with the pele- 

 cypod Lima dehiscens. The increased bi- 

 omass in polluted areas results from an 

 increase in number of deposit feeders at the 

 expense of filter feeders. 



Little study has been made of the animals 

 on the island shelves, but a single large sam- 

 ple from off Santa Catalina Island was re- 

 ported by Mattox (1955) to contain at least 

 115 species and nearly 500 individuals. Its 

 bioindex of 4.3 is a little lower than the aver- 

 age value of those on the mainland shelves 

 but is within their range of variation. Ten 

 large samples from the shelf off the north- 

 west end of Santa Catahna Island (Figs. 146, 

 147) had an average biomass of about 100 

 grams/sq meter. Four species of three 

 genera of brachiopods are common off this 

 island, and repeated samphng over many 

 years appears to indicate fluctuations in their 

 numbers. 



Benthonic foraminiferans from the shelves 

 have been the subject of several studies by 

 geologists who wished to apply a knowledge 

 of modern ecology to problems of ancient 

 sedimentary rocks. One of these problems, 

 the question of degree of reworking of fos- 

 sils from older rocks into later sediments, 

 was investigated by Crouch (1954), who 

 found that about half the total number of 

 foraminiferal tests in modern sediments of 

 San Pedro Bay consist of reworked fossils of 

 Miocene to Pleistocene age. This serves as 

 an obvious warning against too easy an ac- 

 ceptance of foraminiferal tests as indicative 

 of the environmental conditions at any site 

 of sampling. Zalesny (1956), studying fora- 

 miniferans in Santa Monica Bay, also found 

 considerable reworking of fossil forms into 

 modern sediments. Modern foraminiferans, 

 both dead and living tests, show a systema- 

 tic variation with depth so that different 

 assemblages occur on the shelf, slope, can- 



