ECOLOGICAL FACTORS 



401 



(Fig. 221) and is also dependent on temperature. At 15° C. it is 

 15 foot-candles for Macrocystis, 38 foot-candles for Fucus serratus 

 and 32 foot-candles for Laminaria saccharina. 



Assimilation is affected not only by light intensity but also by 

 temperature and both factors need to be studied together. Some 

 recent work on Macrocystis pyrifera in California has shown that 

 the net photosynthesis varies not only with depth, as evidenced by 

 the rates exhibited by blades from different positions on the plant, 

 but also with temperature. 



Table 17 



Plants 1-4 all reached the water surface. 



Ehrke (1931) suggested that there is a correlation between the 

 temperature at which maximum assimilation takes place and the 

 average temperature of the month of maximum development (see 

 table below). 



Table 18 



Optimum temperature Av. temperature in months 

 for assimilation of max. development 



Genus 



17° C. 

 o°C. 



17° C. Aug.-Sept. 

 0° C. winter and early 

 spring 



Fucus, Enteromorpha 

 Delesseria 



