ZoBell 



16 



Marine Microbiology 



points out that a small correction must be introduced for changes in sea 

 water resulting from the heat of fusion and the heat of dilution, the cor- 

 rected factor being 12.08. Therefore the osmotic pressure of sea water at 

 0° C. equals 12.08 X A. If the osmotic pressure at 0° C, OPo, is known, 

 the osmotic pressure at any other temperature, OPt, can be calculated 

 from the following formula: 



OPt = OPo X 



273 + t 

 273 



The osmotic pressure, density, and salinity of sea water of different 

 chlorinities are summarized in Table III. The osmotic pressure of sea 

 water of average salinity, 3S.oo°/oo, is 23,07 atmospheres at 0° C. or 24.69 

 atmospheres at 20° C. 



Table III. — The salinity, density, freezing point, and osmotic pressure of sea water of 

 dijfferent chlorinities at o" C, calculated from Knxjdsen'j (iqoi) Hydrographical Tables: — 



Chlorinity C/oo) 

 Salinity (Voo) 

 Freezing point (°C.) 

 Osmotic pressure (atmospheres) 

 Density (at 0° C. referred to 

 dist. water at 4° C.) 



17.00 



30.72 



— 1.67 



20. 17 



19.00 



34-33 



-1.87 



22.59 



1.02758 



19.38 



3S-OI 



-1. 91 



23.07 



I. 02814 



37-94 

 -2.08 



25-13 

 I . 03049 



Most marine organisms are stenohaline, or adaptable to only slight 

 changes in salinity or osmotic pressure. Those which are able to live in 

 water having a wide range of salinity or osmotic pressure are termed 

 euryhaline. Certain crustaceans and the salmon are outstanding exam- 

 ples of euryhaline organisms. Some bacteria thrive in fresh water and 

 others live in the most concentrated brines, but most of the bacteria and 

 allied microorganisms found in the sea at places which are remote from 

 possibilities of terrigenous contamination tend to be stenohaline (see 

 Chapter VIII). Contrary to popular conception, marine microorganisms 

 tolerate hypertonic solutions no better than they tolerate hypotonic 

 solutions. 



The hydrostatic pressure of sea water is primarily a function of depth 

 and secondarily of temperature, chlorinity, compressibility, and latitude. 

 For practical purposes the effect of atmospheric pressure on the hydro- 

 static pressure is not generally considered. In fact, for biological purposes 

 only the depth need be considered. 



Roughly, the hydrostatic pressure increases one atmosphere for each 

 ten meters, an atmosphere being 15 lbs. per square inch or the weight of a 

 760 mm. column of mercury. At a depth of one mile the pressure approx- 

 imates one ton per square inch. There are few land-dwelling organisms 

 which can tolerate such pressures. Very little is known concerning the 

 effect of pressure on marine organisms but certainly it does not exclude 

 life from the abyssal regions of the sea. Living organisms have been re- 

 covered from the greatest depths dredged. Bacteria appear to be more 

 abundant in bottom deposits than elsewhere in the sea, regardless of the 

 depth of overlying water or the pressure. 



The pressure influences the solubility of substances although the effect 

 of pressure on the chemical or physical properties of sea water is consider- 

 ably less than that of temperature or salinity. The effect of pressure on 

 sampling apparatus must be taken into consideration because unless ade- 

 quately protected, thermometers and other instruments will be broken by 

 the pressure at great depths. 



