212 RILEY 



carbohydrate, suggesting partial utilization of this material. Earlier, Gordon 2 had 

 treated collections of deep-water particulate matter with a mixture of trypsin, 

 chymotrypsin, and amylase and had found that about 20% of the organic matter 

 was hydrolyzed. 



Riley 1 attempted to assess the feeding capabilities and food requirements of 

 deep-water bathypelagic fauna by analogy with experimental information on 

 cold-water surface populations, and he assumed, on the basis of Gordon's work, 

 that about 20% of observed average concentrations of particulate matter could 

 be utilized. The conclusion was that this kind of material could only be a food 

 supplement, supplying at most about 20% of food requirements. However, these 

 crude assumptions sweep some very large questions under the rug. We know 

 essentially nothing about feeding capabilities or food requirements of deep-water 

 organisms, so that the analogy with surface forms may or may not be valid. We 

 also know nothing about their digestive capabilities, so that in vitro experiments 

 with digestive enzymes may not give a realistic impression. 



Selective feeding on larger particles or on organisms may make up for the 

 apparent deficit. Or, as indicated earlier, there is considerable random variation 

 in the quantity of particulate matter. The extent of this variation has not been 

 carefully determined, but it is possible that the sparsity of deep-sea fauna may 

 be controlled not so much by general impoverishment as by the improbability 

 that any considerable number of animals will find the limited number of 

 microhabitats that contain abundant food. All these possibilities that have been 

 mentioned are ripe for further investigation. 



Turning now to the bacteria and small algae in deep water, we note that 

 experiments 2 ' 7 have shown normal deep-water populations to be capable of 

 absorbing C-labeled sugars and amino acids at concentrations of 10" 7 to 

 lO^/W, and apparently this applies to algae as well as bacteria. 28 Rates of uptake 

 varied for different kinds of substrate that were used, so that the results were 

 not very meaningful ecologically, but, in general, they indicated that bacterial 

 increase might be of the order of 10% per day. This is miniscule compared with 

 optimal bacterial growth but is indicative that maintenance of a population is 

 possible in deep water. This conclusion is reinforced by the fact that 

 concentrations of free amino acids are one to two orders of magnitude larger 

 than the minimum limits required for observable uptake. 1 6 



Finally we come to the point of trying to put the whole thing together. Not 

 only in the surface layer but in the whole vertical column, there are regional 

 variations in particulate matter in the North Atlantic 1 and the North Pacific 5 

 which appear to be related to geographical variations in surface production. The 

 effect of surface production apparently is more important than horizontal 

 dispersion in deep water, although a few cases have been noted in which there 

 are vertical variations associated with particular water masses 6 or seasonal 

 variations that probably are associated with water-mass transgressions. 1 ' 2 9 



The high concentration of particulate matter underlying productive areas can 

 hardly be explained in terms of passive sinking from the surface. Moderately 



