LIGHT IN MARINE ECOSYSTEMS 265 



indicate arbitrary units of temperature-conditioned respiration. If 

 we assume that the optimal respiration rate is reached at a level 

 of five such units, then the animal will live near the surface during 

 darkness (A). By increasing the light, there will be an increase in 

 respiration say by four arbitrary units. Total respiration would 

 then rise to 9 units which far exceeds the optimum. Animals will 

 then leave the surface zone and descend to a level where respiration 

 is again at an optimum of five units conditioned by light and 

 temperature together (B). It is stressed that this is merely a 

 tentative idea and needs further investigation. Furthermore, there 

 may be other factors which influence respiration, as for example, 

 the quality and quantity of food or metabolic substances in the 

 environment derived from other animals and plants. 



An increase in temperature and light intensity as well as dilution 

 of sea water will cause an increase in respiration. That does not 

 necessarily mean that the mechanism for a reaction is the same in 

 all organisms. A rise in temperature induces an increase in the 

 entire metabolism; fluctuations in salt content cause a change in 

 the state of hydration of the protoplasm and releases osmoregu- 

 latory processes; the effect of light may be found in its efTect on 

 any endocrine system. These questions must be investigated. 

 It should be noted that the two sexes may react quite differently 

 as may the various developmental stages. In addition, there may 

 be some adaptations which differ in their reactions in the field 

 and in the laboratory. 



Finally, two other phenomena must be mentioned in connection 

 with the climate of light in the sea. There are vitamins whose 

 synthesis is dependent on light. Thus, none of them can be pro- 

 duced at great depths. Deep-sea animals may suffer for their lack 

 or get their supply in a roundabout way. The cartilaginous nature 

 of the skeleton in deep-sea fishes, for instance, is said to be due to 

 an avitaminosis. In this connection, the following points must be 

 considered. (1) According to Fisher (Fisher et al., 1955; Fisher and 

 Goldie, 1959), the Euphausiacea are especially rich in carotenoids 

 and in vitamin A. These animals undergo extensive vertical 

 migrations and serve as the principal source of food for other 

 animals at greater depths. Thus, vitamins are transported through 



