T. F. GOREAU 275 



posited ill the skeleton as CaCO^, and that these are brought to 

 the calcification site by separate pathways ( 3 ) . In order to test this 

 directly we developed a technique in which the uptakes of Ca"*' 

 and C^^ carbonate were measured simultaneously in a variety of 

 calcareous coelenterates and algae, under natural conditions in the 

 reef. As before, light and dark runs were carried out simultane- 

 ously, the experiments lasting lietween five and six hours. After 

 washing and drying the specimens, activities due to Ca^' and C^^ 

 deposited in the skeleton were quantitatively isolated, and sep- 

 arated from the C^^ activity fixed in the coenosarc as organic mat- 

 ter by photosynthesis of the zooxanthellae. A detailed description 

 of this technique will be published later. 



The data in Table I summarises results of field experiments 

 carried out for the purpose of measuring simultaneously calcium 

 and carbonate transfer rates from the medium into the test organ- 

 isms. The plants and animals used in these investigations, and list- 

 ed in Table I, belong to three different ecological categories: Group 

 1 consists of shallow water ahermatypic coelenterates which contri- 

 bute only insignificant amounts of calcareous matter to the reef; 

 Group 2 contains three hermatypic coelenterates which are chiefly 

 reef framework builders; Group 3 has three hermatypic algae, the 

 remains of which form the bulk of the fine calcareous lagoon and 

 slope sediments. All these species are found in the actively grow- 

 ing part of the reef rampart at Maiden Cay, Jamaica, where these 

 experiments were carried out. 



The first two columns of Table I give the transfer rates of Ca"*^"^"*" 

 and HC^^O^g into the mineral skeleton, the third column gives 

 the rate of photosynthetic fixation of C^'' into organic matter, e.g. 

 the primary producti\'ity. In the ahermatypic coelenterates lacking 

 zooxanthellae, there are no significant light-dark differences in the 

 calcium deposition rates, but in the hermatypic coelenterates con- 

 taining zooxanthellae and in the hermatypic algae, these differ- 

 ences are extremely pronounced. An exception was the red alga 

 Ampliiroa where the calcification rate in darkness was much higher 

 than in light. Not unexpectedly, the organic carbon fixation val- 

 ues observed in ahermatypic species were extremely low, and were 

 probably due to heterotrophic exchange, or photosynthesis of bor- 

 ing algae in the skeleton. 



