4 Marine Microbiology 



and its bottom sediments. Besides the basic task of studying 

 microorganisms for their own sake, the marine microbiologist 

 must also be concerned with (a) the effects of microorganisms 

 on higher plants and animals and the productivity of the sea, 



(b) stimulating and inhibitory effects of microbial metabolites, 



(c) microbes as agents of disease, (d) their role as geochemical 

 agents and in the diagenesis of marine sediments, ( e ) microorgan- 

 isms as indicators of the origin, movement, and properties of 

 water masses, (f) a study of tlie unique properties of marine 

 microorganisms which might contribute fundamentally to a bet- 

 ter understanding of the origin and processes of life, ( g ) problems 

 of microbial corrosion, deterioration, fouling, and spoilage of 

 materials of economic significance, (h) fate in the sea of micro- 

 organisms of sanitary significance, and (i) many other problems. 



SALINITY OF NATURAL WATERS 



Approximately 72 per cent of the earth's surface is covered 

 with water. Exclusive of juvenile water in the primary lithosphere, 

 more than 98 per cent of the world's water occurs in the sea 

 or its sediments ( 18 ) . About 1 per cent occurs in polar and 

 continental ice. Inland waters (freshwater lakes, rivers, reservoirs, 

 marshes, soil moisture, circulating ground waters) and atmos- 

 pheric moisture account for less than 0.2 per cent of the world's 

 water. 



The salt concentration in the hydrosphere ranges from less 

 than 1 ppm in certain alpine lakes, increasing in amounts in river 

 mouths and estuaries to about 35%c in the open ocean. Ten 

 times this amount, or full saturation, occurs in certain land- 

 locked salt water bodies. Remote from the influence of melting 

 ice, large rivers, heavy rainfall, or excessive evaporation, the 

 sahnity of ocean waters ranges from 33 to 38 %c. In many 

 localized coastal areas ocean water gradually blends with fresh 

 water from rivers or rain to become brackish. Excessive evapora- 

 tion in other localized areas where there is little mixing may 

 result in superhalinity as in salt marshes and salt lakes. 



The majority of the microorganisms when taken directly 

 from the open ocean (water as well as bottom sediments) re- 



