LIGHT IX MARIXE ECOSYSTEMS 263 



respiration in August depends on the stronger light intensity at 

 that time. These examples stress the need for further research on 

 the combined effects of light and temperature. Indeed, it will be 

 desirable to compare animals from the eulittoral, sublittoral, and 

 bathyal as well as those from equatorial and polar regions. 



There is still another factor to be investigated in connection 

 with light. From many ecological comparisons and experimental 

 investigations we learn that penetration of marine organisms into 

 brackish water depends on the temperature and oxygen content 

 of the water (see references in Remane and Schlieper, 1958). 

 Evidently this also depends on light, for many animals seem to 

 prefer dark habitats on entering brackish or fresh water. I also 

 wish to remind you of the numerous inhabitants of caves (see 

 summary by Thienemann, 1950) and of coastal ground water. 

 Remane and Schulz (1935) pointed out the eventual dependence 

 on light. According to Sernow (1958), Brodski discovered Forami- 

 nifera living in springs of the Karakorum Desert in salinities of 

 5 to 11 %Q, whose nearest living relatives are found in the 

 Mediterranean. The hydroid polyp Cordylophora lacustris prefers 

 shady or dark places when living in fresh water (Roch, 1924). 

 Kinne (1956, 1959) also has some interesting data on this animal. 

 The amphipods Talitrus and Orchestia and their relatives live on 

 beaches above the high water mark. They protect themselves 

 against the light by burrowing into the sand. According to Rullier 

 (1954) "I'abri est necessaire pour les tubes jeunes" of the brackish 

 water polychaete Mercierella. Furthermore, the effect of light 

 should be taken into consideration in the so-called brackish water 

 submergency of Remane (1940, 1955, 1958). 



Without doubt we can establish by statistical comparison a 

 correlation between darkness or weak light intensities and the 

 dilution of sea water. From this, we may deduce that penetration 

 of marine organisms into dilute sea water is facilitated by the 

 absence of light. This idea must be verified by experimental work. 

 There is, however, one contradictory fact. Phototactic and photo- 

 tropic reactions in some animals are affected by factors other than 

 light, such as temperature, salt content, oxygen, or carbon dioxide. 



In short, we have considered the following phenomena. (1) Light 



