COMMUNITY ORGANIZATION: METABOLISM 



499 



subject. This is lamentable, since bacteria 

 are fundamental to the formation and 

 maintenance of any terrestrial or aquatic 

 community. The formation of calcium 

 nitrate, sulfate or phosphate by soil bac- 

 teria is as important in the community as, 

 say, the production of hormones in the in- 

 dividual organism. 



Bacteria are fundamentally important in 

 the metabohsm of aquatic communities. 

 The activities of these organisms in such 

 communities are not so well understood as 

 the bacterial processes in soils. The general 

 outline of activities of aquatic bacteria fol- 

 lows the usual pattern. Lifeless plankton, 

 nekton, and benthos are decomposed by 

 heterotrophs, to help set up the gradient in 

 organic materials previously discussed (p. 

 443), and their proteins are broken down to 

 ammonia; the ammonia eventually is oxi- 

 dized to nitrates by aquatic autotrophs. The 

 nitrates are available to the phytoplankton 

 in their synthesis of organic compounds. 



There is an interesting difference be- 

 tween aquatic and terrestrial communities. 

 In both groups the heterotrophic bacteria 

 break down protoplasms to ammonia, and 

 autotrophs build up ammonia and other 

 materials into salts capable of being used 

 by the primary green plants. In terrestrial 

 communities the resulting salts are formed 

 by bacteria and used by the root systems 

 of green plants in the same stratum, viz., 

 the subterranean; whereas in aquatic com- 

 munities, especially those with any con- 

 siderable depth, the phytoplankton that 

 must use these salts live chiefly in the up- 

 permost strata, which, as a consequence of 

 their photosvnthetic function, form the 

 analogue of the canopy stratum of forests. 

 In this case, then, the depletion of salts in 

 the epilimnion and their accumulation in 

 the hypolimnion make necessary the re- 

 plenishment of the epilimnion by upward 

 diffusion of salts from the lower zones 

 through partial solution pressures and 

 by convection currents. In both types of 

 communities the results are the same, and 

 the basic processes are similar; the density 

 of the interstitial medium and the size of 

 the individual photosynthetic units are dis- 

 similar. 



The roles of marine bacteria are gener- 

 ally similar to those of fresh-water and ter- 

 restrial bacteria, but certain complexities 



render the marine problem much less un- 

 derstood. 



For example, there is nothing now 

 known concerning pressure or temperature 

 that would inhibit the growth and repro- 

 duction of abyssal bacteria (ZoBell, 1934, 

 1946), and yet too little is known to justify 

 wholesale transference of facts from soil 

 bacteriology to marine bacteriology. 



One difficulty is in the great distances 

 through which decomposing organisms 

 must fall. Whereas in a forest or a lake 

 community, a disintegrating organism may 

 fall from several to a hundred meters, and 

 decomposition takes place largely in the 

 lowermost strata, the decomposing organ- 

 ism in the open sea might sink through 

 distances up to 10,000 meters. It has been 

 pointed out (Coker, 1938, 1947, p. 85) 

 that, since the predominant marine organ- 

 isms are minute, their sinking rate is slow. 

 Protozoans, diatoms, and coccolithophores 

 sink gradually, while even a large copepod, 

 falling at the rate of 2 feet per minute, 

 would cover only a mile in two days. Since 

 the available food supply for animals of the 

 intermediate strata, between the photic 

 zone and the abyssal zone, must be derived 

 in large part from this falling and decom- 

 posing food, not much disintegrating ma- 

 terial would reach the bottom strata direct- 

 ly. The smaller dead creatures, certainly, 

 would be wholly decomposed. Coker con- 

 cludes that, barring deposition of skeletons, 

 there is no great accumulation of solid or- 

 ganic waste on the sea floor. If this is so, 

 then the heterotrophic bacterial industry, 

 so essential to community metabolism, 

 would be relatively smaller in the marine 

 floor stratum and relatively greater in the 

 intermediate strata than in fresh-water com- 

 munities. In fresh-water lake communities 

 the difference from the marine zonation in 

 this respect becomes progressively less in 

 proportion to the depth of the lakes. 



There is a great accumulation of dis- 

 solved organic material in the upper and 

 intermediate levels of the sea. Krogh 

 (1934) estimated that such dissolved or- 

 ganic materials are equivalent to 300 times 

 the quantity of living organisms in these 

 areas at any given time. He further postu- 

 lated that this vast amount of organic sub- 

 stances has largely gone out of circulation; 

 that it is no longer available for the metab- 

 olism of the community. 



