NO. 1 HARTMAN, BARNARD: BENTHIC FAUNA OF DEEP BASINS 15 



of heavy-shelled mollusks were captured. Sampling broader and deeper 

 areas in this basin may reduce the average biomass values to levels near 

 or below those in Santa Monica and San Pedro Basins. 



The best sampled outer and deeper basin, Santa Catalina, with 

 higher subsill dissolved oxygen values, has a biomass of about 8.7 grams 

 per square meter ; it has many more species and denser populations than 

 do the nearshore basins (Table 1). The single samples and photographs 

 of other offshore basins indicate that biomass values are larger in the 

 deeper basins than in the shallower nearshore basins. 



Identical sampling procedures have been used in shallow waters of 

 the coastal shelves and considerable unpublished data have been used to 

 provide the following comparisons with the basins. On the shelf along 

 the Palos Verdes Hills, in shallow waters of 13 to 18 m depth, lives a 

 rich Chaetopterus-Lima association, comprising about 75 species of 

 animals in the association. These shallow bottoms support standing crops 

 of approximately 4000 grams and about 2400 animals per square meter. 

 Other bottoms dominated by ophiuroids, in depths of 30 to 80 meters, 

 support about 500 grams of biomass, 1700 animals per square meter, 

 distributed among 250 species. 



It may be seen that the standing crops in the basins are quite low in 

 comparison with the rich coastal shelves. The impoverishment of the 

 nearshore basins and their proximity to highly productive shallow bot- 

 toms and neritic waters is indirect evidence that the supply of reworked 

 debris and detritus to the shallow basin floors is considerably greater 

 than to the deeper basins. This is seen clearly in the samples from near- 

 shore basins, which when washed and screened, leave large residues of 

 dead organic materials. Thus, a considerable excess of organic matter 

 which has not been recycled through benthic metazoans is available to 

 bacterial processes in the shallow basin sediments. 



Biomasses of the better sampled basins correspond favorably with 

 data reported by Zenkevitch and Birstein (1956, p. 55, 6.94 grams 

 per square meter) for depths of 950 to 4070 meters on slopes near the 

 Kurile Trench in the North Pacific Ocean. 



Bio-index is an expression of the total population of animals in a 

 sample relative to the diversity of that population, that is, the ratio of 

 total animals to total species. Along the coastal shelves of southern Cali- 

 fornia in depths of less than 100 meters, bio-indices of individual samples 

 covering an area of 0.25 square meter can be expressed in the range of 

 5.0 for ophiuroid bottoms up to 23.0 for algal or kelp holdfast bottoms 

 which are in depths of less than 10 meters. In the former case the typical 



