UTILIZATION OF SOLAR ENERGY 1?V AQUATIC ORGANISMS 



37 



incident on tlie surface of lakes or oceanic 

 areas is absorbed by the water itself or by 

 detritns and that only a very small part 

 can be ntilized by plants or animals. We 

 conclnde tliat aqnatic organisms are exist- 

 ing under very unfavorable circumstances 

 in regard to the utilization of solar energy. 

 It is for this reason that tlie intensity, 

 amount, and composition of the light are so 

 frequently found to be limiting or highly 

 significant factors in the aquatic environ- 

 ment. Attack on the unsolved problems 

 outlined above is therefore urgent, and the 

 extension of our present observations into 

 other bodies of water and particularly over 

 longer periods of time is of tlie greatest 

 importance. 



Summary 



The amount and nature of daylight in 

 natural waters depends upon the surface 

 loss, the selective absorption of the water 

 itself, and the selective action of particulate 

 and dissolved material. Further changes 

 in the ilhunination result from differences 

 in transparency with depth and with the 

 season, dilferences in the length of day, and 

 differences in the angular distribution of 

 the light. 



The biological significance of ultraviolet 

 in natural waters is in doubt, but the visible 

 component of light is important in the regu- 

 lation of the activity of many animals, in 

 the vision of fish, and especially in the 

 photosynthesis of the plants. Since the 

 utilization of light is very low even under 

 the most favorable circumstances, it is un- 

 derstandable that light is so frequently a 

 limiting factor in the aquatic environment. 



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