Physiological Significance of Light in Marine 



Ecosystems 



HERMANN FRIEDRICH 



histitut fiir Mecresjorschiing, Bremerhaven, Germany 



GENERALLY speaking physiological research has two different 

 aims: (1) it recognizes fundamental life processes within cells and 

 protoplasm and (2) it assists in understanding the functional 

 relations of organisms as a whole to their environment. In other 

 words, the first objective of research is the individual organism 

 itself, whereas the second is its relationship to environment. 

 Naturally these are closely related and there is considerable 

 overlapping between the two. However, different methods are 

 necessary, and a clear distinction between them is possible. The 

 title of this paper indicates that I shall deal only with the second 

 aspect of the research, which may be called ecological physiology. 



There are two methods used in ecological-physiological research. 

 It is possible to find correlations between the appearance, distri- 

 bution, abundance, and behavior of organisms and the distribution 

 of environmental factors and their fluctuations. The parallel 

 variations both of the organisms and of factors in their environ- 

 ment suggest conclusions that a given reaction depends on a 

 certain factor. Vertical migrations of zooplankton, which parallel 

 fluctuations in light intensity, provide a classic example for 

 reasoning based on this sort of evidence. 



Naturally there are many disadvantages in making such 

 statistical comparisons. Only the more obvious interdependencies 

 are detected, and exact information of physiological conditions 

 within the organisms is lacking. Also, the method fails almost 

 completely when reactions of the organisms are determined by 

 several environmental factors. To some extent, these disadvantages 

 can be overcome by laboratory experiment. In tests it is possible 



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