PHOTOSYNTHESIS IN CORAL - ALGAL ASSOCIATIONS 



J. Morgan Wells and Anna H. Wells 



Wrightsville Marine Bio-medical Laboratory 



Wilmington, North Carolina 



ABSTRACT 



Measurements of the rates of photosynthesis or respiration 

 of coral-algal systems were made under a variety of natural 

 light conditions and artificially imposed darkness. The 

 maximum photosynthetic rate was found to be from 1.1 to 2.9 

 times the respiratory rate, depending on species. This 

 means the potential exists for corals to obtain a major 

 portion of their nutrition from algal symbionts. 



INTRODUCTION 



The existence of physiological symbiosis involving algae and invertebrates is a 

 well-known fact (1-4) . While there has been considerable speculation as to the 

 exact nature and magnitude of the interdependence of algae and invertebrates, 

 little direct quantitative information is available. 



On the basis of changes in the oxygen concentration and plankton densities of 

 water flowing over coral reefs, Odum and Odum (5) have concluded that coral 

 reefs are essentially self-sustaining systems and are not dependent on outside 

 sources of nutrition. Kawaguti (6) reports on excess of O2 over CO2 production 

 in some reef corals. Likewise, Wells and Haxo (7) have measured a three-fold 

 increase in Oo production in light over consumption in darkness in several 

 species of tridacnid clams and coral Pocillopora damicornis . While such measure- 

 ments do establish the maximum photosynthetic rate of the association, they do 

 not in themselves define the contribution which the photosynthetic products make 

 to the metabolic budget of the invertebrates. 



Muscatine (8), however, has shown that in the presence of homogenated animal 

 tissue, zooxanthellae from the respective animal (coral or tridacnid clam) lib- 

 erate from 35-5070 of the photosynthetic products, of which glycerol comprised 

 about half. Liberation of photosynthesates was negligible in the absence of 

 animal homogenate. 



Goreau (9-10) has suggested still another aspect of the relationship of coral 

 and algae, that being the facilitation of calcium deposition by the photosyn- 

 thetic activities of the algae. This view is supported by his finding that 

 carbonic anhydrase inhibitors reduce the rate of calcification as much as 517o 

 in light, and the inhibitor and darkness another 34%. 



OBJECTIVE 



It was the purpose of this investigation to determine the magnitude of the poten- 

 tial contribution of zooxanthallae to the metabolic budget of corals. In situ 

 measurements of photosynthetic capacity and respiration of coral-algal systems 

 were made under a variety of natural light conditions, and in artificially 

 imposed darkness. 



VI-239 



