Chapter VI — 97 — Bottom Deposits 



Furthermore, any viable population of a given environment at any par- 

 ticular time is merely an expression of the dynamic balance between the 

 rate of death and the rate of multiplication of the organisms. Since the 

 generation time of bacteria is considerably shorter than that of the other 

 organisms tabulated above, bacteria may be a more important component 

 of mud than indicated by the tabulated values. Thus, in spite of the fact 

 that large numbers of bacteria are ingested by animals, they are rapidly 

 replaced by reproduction. 



Mare (1942) defines macrobenthos as the large animals living in the 

 mud. Meiobenthos consists of bottom-dwelling copepods, small poly- 

 chaetes, lamellibranchs, nematodes, Foraminifera, and other fauna of 

 intermediate size. Microbenthos consists of protozoans, exclusive of the 

 Foraminifera, and other unicellular organisms in the mud. She found the 

 macrobenthos to be confined largely to the topmost 10 cm. of mud. The 

 meiobenthos, microbenthonic fauna, and diatoms were largely confined 

 to the topmost 0.5 cm. of mud. Bacteria were more abundant at the sur- 

 face than at a depth of 3 cm., but large numbers of bacteria were found at 

 all depths examined for their presence. Since with few exceptions animals 

 are dependent upon free oxygen, they are restricted to the surface layers 

 of mud. Relatively few animals occur in bottom deposits at depths ex- 

 ceeding 10 cm. 



Using the direct microscopic technic for estimating the abundance of 

 bacteria, Butkevich (1938) estimated that the biomass, or total weight, of 

 bacteria per unit volume of mud was about the same as the biomass of 

 plankton algae in the Caspian Sea near the mouth of the Volga River. In 

 bottom desposits the biomass of bacteria exceeded that of plants. 



Kinds of microorganisms occurring in bottom deposits : — In the up- 

 permost layers of mud, aerobic bacteria appear to be more abundant than 

 anaerobes. This may be due to limitations of the anaerobic media used 

 for estimating the abundance of anaerobes, since the examination of col- 

 onies isolated from plates which have been incubated in the presence of 

 oxygen reveals that a majority of them are facultative aerobes. Actually 

 over 90 per cent of the colonies which have been isolated from either 

 aerobic or anaerobic plates have proved to be facultative aerobes. Most 

 of them grow much better in the presence of oxygen than in its absence. 

 'As a matter of fact, relatively few strict anaerobes have been isolated 

 from marine mud. It should be pointed out, though, that in spite of the 

 fact that anaerobic conditions predominate in bottom deposits, most 

 workers have used aerobic procedures exclusively in studying the micro- 

 flora of mud. 

 / The predominant bacteria which Lloyd (1931a) isolated from Clyde 

 I Sea mud were small, Gram-negative, asporogenous rods resembling the gen- 

 era Achromobacter and Chromobacterium. In lesser abundance she found 

 Gram-negative diplococci and sarcinae, relatively large spore-forming 

 bacilli, and a few slow-growing spirilla. Lloyd characterized the bottom 

 flora as being "true water bacteria." Conversely, Russell (1891) re- 

 ported that most bottom-dwelling bacteria differed from those in the over- 

 lying water, although many were common to the water as well as to the 

 mud in the Bay of Naples. 



It has been our experience that the colonies developing in plates inocu- 

 lated with marine mud differ grossly from those inoculated with sea water. 

 While many of the bacteria are common to both habitats, some mud-dwell- 



