QUANTITATIVE SURVEY OF THE 



BENTHOS OF SAN PEDRO BASIN, 



SOUTHERN CALIFORNIA 



PART II 



FINAL RESULTS AND CONCLUSIONS 



INTRODUCTION 



This is a continuation and conclusion of the study of the San Pedro 

 area for which preliminary results have been published (Hartman, 1955). 

 This area ( IVIap 1 ) lies between the mainland of southern California 

 and Santa Catalina Island (Map 2), in 33° and 34° north Latitude, 

 and 117° to 119° west Longitude. The submarine lands comprise more 

 than 1060 square miles, of which the shelf lands make up about a fourth, 

 the slopes and canyons together about half, and the San Pedro Basin 

 nearly a fourth. The terrain is rugged, consisting of shelf, slope, canyon, 

 basin and sea mount features; depths range from a few to 495 fathoms. 

 This large, partly enclosed, oceanic area receives not only the discharge 

 of the Los Angeles, San Gabriel and Santa Ana Rivers which drain the 

 slopes of the lofty San Gabriel and San Bernardino Mountains, but also 

 the liquid effluent wastes of populous Los Angeles County. As a result, 

 much terrigenous material is carried downstream to the sea, where long- 

 shore currents, chiefly with a southeasterly drift, pick up the loads, to 

 deposit the coarser gravels along the beaches and shallow shelf ; the 

 sands, silts and muds are carried successively farther out, or may be 

 deposited in the canyons and San Pedro Basin. All but the finest particles 

 may have been filtered out before the nutrient-rich waters reach the 

 outer shelf and slope. As a result, the long-shore shelves and slopes are 

 heavily populated with a richly diversified benthic fauna, which attains 

 its maximum development along the Pales Verdes and the San Pedro 

 shelves. These benthic populations chiefly represent a few groups, includ- 



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