56 Marine Microbiology 



meters of sea water. Even the highest estimates based on viable 

 counts would be two to three magnitudes too small. If one utilizes 

 population values derived from direct microscopic counts, the 

 discrepancies disappear to a considerable extent but such data 

 must be viewed with suspicion. The counting errors involved in 

 the technique and its failure to distinguish between active and 

 inactive cells needs no discussion. It is more important to point 

 out that one can calculate the oxygen demand of certain typical 

 basin sediments from the decrease in organic matter with depth 

 in the sediment (7) and then convert this to standing crop of 

 bacteria by assuming a "reasonable" value for the respiration rate 

 of a bacterial cell in the sediment. If this is done, one finds tliat 

 the calculated standing crop falls well within the range of viable 

 counts obtained for such sediments. In the sediments, therefore, 

 there is no need to postulate more active bacteria than can be 

 found by viable counting procedures. Although there may well be 

 nutritional differences between the bacteria in the water and 

 in the sediments, as is indicated by the data of Skerman (22), 

 there is no reason to suspect that a significantly lesser per cent 

 of the active water flora should be detected by the plating proce- 

 dures commonly employed in current marine investigations. 



This reasoning leads to the conclusion that bacteria play a 

 very minor role in the regeneration of carbon in the upper layers 

 of the ocean where the bulk of the process is going on. This 

 conclusion is not new of course, having been arrived at earlier 

 by Riley ( 19) who ascribed most of regeneration in the upper and 

 mid depths to the activities of the phytoplankton and the animals. 

 If the above arguments are valid, they also imply that the 

 standard minerlization cycles as worked out for the soil cannot 

 be applied a priori to the marine environment. 



What applies to carbon also applies to nitrogen. The increase 

 in C/N ratio between the plankton and the organic matter in 

 the surface of marine sediments indicates tliat nitrogen must be 

 regenerated relatively faster than carbon, so that the assumption 

 of 90 per cent regeneration in the upper 200 meters appears 

 reasonable. Following the same pattern of calculations used 

 above, a release of roughly 0.02 /-g nitrogen per liter per hour is 

 found. If all the released nitrogen were nitrified before being 



