CHAPTER 4 

 RESPIRATION 



The properties of the components of the blood are highly adapted to 

 the function of preserving the constancy of the environment of cells 

 and tissues and to the functions of transporting carbon dioxide and 

 oxygen. For example, the buffer action of a mixture of carbonic acid 

 and its salts is unsurpassed as a means of maintaining a nearly neutral 

 reaction through direct neutralization of acid or base. . . . Not less 

 remarkable is the adaptation of the properties of haemoglobin to the 

 transport of oxygen. All of these functions are performed, however, 

 not by the blood alone, but in co-operation with the lungs, the kidneys, 

 and other organs. 



L. J. Henderson, 1928. Blood: a study in general physiology 



THE ENVIRONMENT 



In addition to water and salts nearly all marine animals are dependent 

 upon a supply of oxygen. The sole exceptions are certain worms which can 

 live for long periods as facultative anaerobes in oxygen-deficient environ- 

 ments, e.g. intestinal parasites and certain inhabitants of muddy shores. 

 The distribution of oxygen and carbon dioxide in ocean water has been 

 described on previous pages (13, 14). Oxygen levels in most marine 

 environments are adequate to sustain life. As we have already noted, 

 oxygen is depleted in deeper waters of certain enclosed basins and fjords, 

 frequently with production of H 2 S, producing lifeless zones. In restricted 

 areas the phytoplankton may accumulate to such a degree that it outstrips 

 herbivores. This material rains upon the bottom, and its gradual decay 

 exhausts the oxygen supply of the water, producing anoxic layers which 

 sometimes occupy a substantial proportion of the water column. Under 

 these conditions heavy mortality of animal life results. 



The littoral environment presents certain peculiar conditions. During 

 the night, when the tide is out, the oxygen content of inter-tidal pools may 

 become greatly depleted, depending upon population-density, plant- 

 growth and other factors (149). The subsurface layers of muddy shores 

 and banks are frequently anoxic owing to decay and oxidation of organic 

 matter. Periods of oxygen scarcity are encountered by burrowing littoral 

 animals during tidal ebb, and various devices are employed for coping 

 with such emergency conditions. Certain inhabitants of the littoral region 

 are amphibious, and here also we find a few species of predominantly 

 terrestrial groups, adapted for submergence, and certain species of marine 

 origin adapted for aerial respiration. Various aspects of respiration among 

 animals have been reviewed by Krogh (100), Guieysse-Pellissier (72) and 

 Bishop (10). 



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