NO. 5 BARNARD: AMPHIPODA 5 



great antiquity that, because of cooling of the deep-sea, found refuge in 

 8% of the sea floor at bathyal depths, then one must balance the conse- 

 quences of greatly decreased living space against a higher food supply 

 per unit of area. Elucidation of the organic-matter cycle awaits experi- 

 mental methods and solution of the uniformity: thermostrophic contro- 

 versy awaits new methods and additional careful study of deep-sea 

 faunas. 



Large particles of organic matter have been discovered frequently in 

 samples from nearshore basins and trenches (Bruun, 1959; Heezen, 

 Ewing and Menzies, 1955) and in the present samples, especially those 

 from Monterey Canyon (see data, Hartman, 1963). Such accumula- 

 tions must indicate that low-density organic matter is transported more 

 quickly and frequently to great depths in canyons before decomposition, 

 than is mineral matter. That organic accumulations probably are dis- 

 posed of by organisms rapidly is shown in the similar organic carbon 

 content of canyon and shelf sediments (Table 1), for if biota (including 

 bacteria) were not disposing of organic matter quickly, the canyon sedi- 

 ments would have much higher organic contents. Nevertheless, the sam- 

 ples containing macroscopic pieces of organic debris have not borne large 

 populations of organisms. This has been observed also in the large ac- 

 cumulation of organic debris off the Santa Clara River on the Ventura 

 coastal shelf, where sediments contain twigs and stems transported from 

 land by the river, probably in great quantities after brush-fires. Here 

 the normally expected high densities of ophiuroids and other character- 

 istic community dominants have been reduced considerably. Most of this 

 debris probably contains a high content of insoluble and poorly-digest- 

 ible residues that few Metazoa are adapted to utilize. Whether it has a 

 toxic effect on benthic populations or whether its presence makes the 

 sediments more difficult to burrow into are problems for experimenta- 

 tion. 



After a turbidity flow, a portion of the formerly buried and labile 

 organic materials that are resuspended probably settle out as a veneer 

 covering the sediments and become available to the first animal immi- 

 grants. Perhaps in ^Monterey Canyon this had occurred just before 

 sampling that poorly diverse population, largely composed of motile or- 

 ganisms such as amphipods and cumaceans. The densest accumulations 

 of debris, fragments larger than 0.5 mm, apparently consisting of surf- 

 grass or eel-grass, were taken at stations 6490 and 6494, in depths of 

 906 and 750 m respectively. The most conspicuous and dominant organ- 

 isms were Protomedeia articulata, a large amphipod, with 20 and 111 

 specimens, respectively, and Leucon sp., a cumacean. The problem re- 



