Chapter VI 



MICROORGANISMS IN BOTTOM DEPOSITS 



It is in the sedimentary materials on the floor of the sea that the 

 microbial population is most extensive and physiologically versatile. 

 Large numbers of microorganisms of various kinds live in the mud or sand 

 where they influence the activities of sedentary or burrowing animals, the 

 diagenesis of bottom deposits, and certain properties of the overlying 

 water. Viable microorganisms have been demonstrated in most samples 

 of bottom deposits examined for their presence regardless of the depth 

 of the overlying water, distance from land, latitude, or the composition 

 of the bottom deposits. 



Numbers of bacteria in sediments: — Certes (1884a) found appreci- 

 able numbers of bacteria in all except four of 100 sediment samples, some 

 of which were collected from water depths as great as S,ioo meters on the 

 Talisman expedition, but his results have no quantitative significance be- 

 cause he analyzed the samples only after prolonged storage. Employing 

 plating methods, Russell (1892) found from 25,000 to 300,000 bacteria 

 per ml. of mud from the Bay of Naples as compared with 10,000 to 30,000 

 bacteria per ml. of mud in the vicinity of Woods Hole, Massachusetts. 

 The bacteria from the Bay of Naples were generally different from the 

 species isolated at Woods Hole, and at both stations the bottom flora dif- 

 fered somewhat from the flora in the overlying water. 



Drew (191 2) demonstrated an average of 160,000,000 bacteria per 

 ml. of mud from the sea floor near Andros Island in the West Indies. Pre- 

 dominating in the lime-rich mud was an organism which Drew described 

 as Bacterium calcis. Gee (19326) estimated that the order of magnitude 

 of the bacterial population of mud from the Florida Keys was hundreds of 

 thousands per gram (wet basis). Lloyd (1931a) found up to 300,000 bac 

 teria per gram (dry basis) of mud from the Clyde Sea. 



Incidentally, the water content of recent marine sediments ranges 

 roughly from 30 to 99 per cent, a factor which should be taken into ac- 

 count in expressing quantitative results. Most mud quantities are ex- 

 pressed on a wet or natural weight basis because this is more representa- 

 tive of the spatial relations of the microorganisms. Unlike soil, in which 

 there may be marked seasonal fluctuations in the water content, the water 

 content of marine bottom deposits varies but little from time to time. 



In the calcareous deposits around the Bahama Islands, Bavendamm 

 (1932) counted up to 16,800,000 bacteria per gram of wet mud. The bac- 

 terial population decreased sharply with core depth. In this same region 

 Smith (1926) found an average of 565,000 bacteria per gram of calcareous 

 mud. Unless otherwise stated all counts refer to aerobes. 



Sediments from the Channel Island region off the coast of southern 

 California were found by ZoBell and Anderson (19366) to contain up to 

 several million viable bacteria per gram (wet basis). Like other workers 

 who have made such studies, they found that the topmost layers of marine 

 sediments generally contained many more bacteria per unit volume than 

 did surface sea water. The bacterial content of the water of the mud- 



