170 



Life 



within the bottom sediments so that the dis- 

 solved oxygen in interstitial waters, origi- 

 nally low, becomes depleted. The produc- 

 tion of hydrogen sulfide by anaerobic 

 bacteria in the top layers of sediment in 

 Santa Barbara Basin serves as an indica- 

 tion of the inhospitality of this bottom en- 

 vironment to animals that need access to 

 free dissolved oxygen. Although measure- 

 ments (Rittenberg, Emery, and Orr, 1955) 

 show that oxygen is not depleted within 

 about 50 cm of the bottom, it is possible 

 that oxygen is depleted in a layer a fraction 

 of a centimeter thick in contact with the 

 bottom where it could inhibit small organ- 

 isms that burrow in the sediment but have 

 siphons or gills reaching to the sediment 

 surface. 



On the bottom of Santa Barbara Basin 

 benthonic animals are few — a deep-water 

 snail Nitidella permodesta, a clam Macoma 

 leptonoidea, and some ophiuroids, sponges, 

 and polychaete worms. Only four species 

 are represented, and bioindices are only 1.5 

 and biomasses 2.0 grams/sq meter. On the 

 side slopes, but still below sill depth, the 

 fauna is richer with an average of 9 species 

 per sample which include the same species 

 present in the deep central area. Bio- 

 indices of these slope samples average about 

 4.0 and biomasses average 65 grams/sq 

 meter. Santa Monica and San Pedro Basins 

 are connected in such a way that the same 



sill controls both. The bottoms of both 

 basins are barren of living benthonic ani- 

 mals (Fig. 148); however, most samples 

 contain empty tubes of the polychaete worm 

 Phyllochaetopterus and the serpulid worm 

 Protis pacifica and numerous tests of a large 

 foraminiferan. The worms are probably 

 vegetative or nonreproductive and reach the 

 bottoms from large populations on the side 

 slopes. That the scarcity of life at depth is 

 not a normal situation is shown by its 

 abundance at the same or even greater 

 depths in other basins. The lower parts of 

 the basin side slopes below sill depth re- 

 semble the flat basin floors in their de- 

 ficiency of life, but at depths just greater 

 than the sill many samples contain living 

 animals, and at still shallower depths aU 

 samples contain living benthic animals 

 (Table 10). Animals of the upper slopes are 

 dominated by siliceous sponges and am- 

 pharetid worms but include many others 

 such as ophiuroids, crustaceans, and mol- 

 lusks. Biomasses increase from zero within 

 100 meters of the bottom of the slopes to 

 probably about 80 grams/sq meter on the 

 slopes shallower than the sill depth. The 

 number of species and bioindices have not 

 yet been worked out in detail, but they ap- 

 pear to be about 20 and 3.5, respectively, 

 for the upper slopes. 



The second kind of basin, having well- 

 populated floors, has been sampled only in 



Figure 148. Impoverished ba- 

 sin areas. The floors of San 

 Pedro and Santa Monica Ba- 

 sins have only occasional dead 

 tubes of a polychaete worm, 

 PhvUochaetoptenis sp., a serpu- 

 lid worm, Protis pacifica, and 

 the dead shells of a scallop, 

 Cyclopecten sp. That of Santa 

 Barbara Basin has a few Uving 

 gastropods, Mitrella permo- 

 desta, a clam, Macoma lepto- 

 noidea, and a few others. In 

 contrast is a rich fauna living 

 on the slopes of the basins 

 above sill depth. 



