18 Marine Microbiology 



to 12 X lO^*" gm per year for the hydrosphere, or from 0.008 to 

 0.08 gm per cubic meter. This amount must be many times more 

 than the quantity of organic carbon cycled annually through the 

 cells of heterotrophic bacteria, Ijecause much of the phytoplank- 

 ton crop is consumed by zooplankton and other grazing animals. 



From all available data on the abundance of bacteria in 

 different water masses, the amount of organic carbon in the 

 standing crop appears to range from as little as 1 X 10~^ gm per 

 cubic meter in many areas of the open ocean to as much as 10 

 gm per cubic meter in certain coastal waters. Unfortunately, 

 quantitative data are too fragmentary to waiTant making an 

 estimate of the average value; even less is known about the rate 

 of reproduction or number of bacterial crops per year. Kriss ( 24 ) 

 estimates the mean range in the standing crop of bacteria in 

 different natural bodies of water as follows : 



Water Body Bacteria per ml Biomass per m^ 



Freshwater lakes 23 x 10^ - 12 x lO^ 9 - 5,000 mg 



Rivers 25 x lO^ - 15 x 10^ 10 - 600 mg 



Inland and shallow seas 3 x 10' - 25 x 10^ 0.6 - 340 mg 



Open oceans 10 - 8 x 10^ .002 - 1.6 mg 



These values may be conservatively small since the bacterial 

 populations were determined by cultural procedures which 

 ordinarily detect only a small percentage of the viable cells. 

 Employing direct microscopic methods for enumerating bacterial 

 populations in shallow marine bays, Oppenheimer and Jannasch 

 (42) found the bacterial biomass to be from 0.18 to 0.9 gm per 

 cubic meter of clear water and up to 10.4 gm per cubic meter 

 of turbid water. 



From the abundance of bacteria in the topmost 0.5 cm of 

 marine mud, Mare ( 34 ) calculated tlie average bacterial biomass 

 to be from 0.07 to 0.36 gm per square meter. It is Interesting to 

 note (Table 5) how this compares with the biomass of other 

 categories of organisms observed in the mud samples. Such data 

 would be more meaningful if we knew tlie generation time and 

 metabolic rates of the organisms. There may be a hundied or 

 more generations of bacteria per year and only one generation 

 of some of the larger organisms. 



