276 



THE BIOLOGY OF HYDRA : 1961 



The primary carbon fixation observed in hermatypic coelenter- 

 ates was due to photosynthesis l3y zooxanthellae. The boring algae 

 were present in only very small amoimts in our samples and it is 

 assumed that their contribution to the total productivity was also 

 very small. Owing to uncertainty of the proportion of the plant 

 biomass in corals, the data are given in terms of total nitrogen, e. g. 

 animal plus plant. The highest calcification and productivity rates 

 were observed in the hermatypic algae. The two species of HaUineda 

 behaved like the hermatypic corals in that calcification was much 

 faster in light than in darkness, but in Amphiroa there was a nega- 

 tive correlation between photosynthesis and skeletogensis. We be- 

 lieve that light inhibition of calcification in this species is pro- 

 duced by a shortage of available carbonate due to competition for 

 CO2 as a common substrate by extremely high levels of photosyn- 

 thesis. This problem is now being investigated in our laboratory. 



There is a positive correlation between the calcium deposition 

 rate and the photosynthetic rate as measured by the specific pri- 

 mary productivity, e. g. the amount of organic matter produced in 



TABLE 1 

 Specific calcification and productivity rates of hermatypic and ahermatypic organisms. 



