Chapter I 



GENERAL INTRODUCTION 



The ocean, which covers nearly three-fourths of the earth's surface, 

 is the home of a vastly diversified plant and animal population. Exclu- 

 sive of insects, about four-fifths of all animal species known to man dwell 

 in the sea, and more than 8000 species of marine plants have been 

 described. 



Although the ocean has been described as the ''world's largest and 

 most efficient septic tank," there are some land-locked biologists who 

 question the existence of bacteria in the sea beyond the littoral zones 

 influenced by contamination from the land. The high salinity of sea 

 water, the paucity of organic matter, the abundance of natural enemies, 

 the processes of sedimentation, the germicidal effect of ultraviolet radia- 

 tions near the surface, high hydrostatic pressures at great depths, and 

 unfavorable temperatures have been credited by some with making the 

 marine environment virtually uninhabitable by bacteria and allied 

 microorganisms. However, it is now known that such microorganisms are 

 widely distributed in sea water and on the ocean floor where they influence 

 chemical, physicochemical, geological, and biological conditions. 



The importance of bacteria in the sea : — The critical examination of 

 water samples from the euphotic zone and of mud from the ocean floor 

 reveals the presence of a biochemically versatile microflora. Some of 

 these microorganisms mineralize organic matter. Others oxidize ammonia 

 to nitrite or nitrate, transform sulfur compounds, liberate phosphate, or 

 otherwise affect the chemical composition of sea water and bottom de- 

 posits. Marine bacteria play an indispensable role as producers of plant 

 nutrients, and the bacteria themselves may be ingested by certain ani- 

 mals as a source of food. 



There are several ways in which marine microorganisms tend either to 

 decrease or increase the hydrogen-ion concentration of sea water or mud, 

 and their activities influence the oxidation-reduction potential. The dis- 

 tribution of oxygen, nitrogen, hydrogen, and probably other gases in the 

 sea is influenced by microbial activity. 



As geological agents, marine microorganisms influence the diagenesis 

 of sedimentary materials in many ways. By their effect on the hydrogen- 

 ion concentration and carbon dioxide tension of sea water, bacteria influ- 

 ence calcium carbonate precipitation. They are believed to be respon- 

 sible for the deposition of iron under certain conditions, and they affect 

 the state of oxidation or reduction of many mineral constituents of marine 

 sediments. Accumulating evidence suggests that marine microorganisms 

 play an important role in the formation, migration, and accumulation of 

 petroleum. 



Besides being essential for a complete understanding of chemical, 

 geological, and biological phenomena in the sea, a knowledge of marine 

 microbiology has numerous utilitarian applications. Bacteria are very 

 troublesome in the spoilage of foods and other marine products of com- 

 merce. As primary film formers, they influence the attachment of seden- 



