EQUIPMENT AND METHODS 



Rates of photosynthesis and respiration were determined by measuring rate 

 changes in the oxygen pressure in closed plexiglass vessels containing coral. 

 The vessels were either 8" diameter hemispheres placed over the corals or for 

 small isolated corals a 3" diameter by 3" high cylinder with a lid. The hemi- 

 spheres were sealed to large coral heads with clay or when placed over small 

 heads on the sand, the edges were covered with sand to prevent mixing with out- 

 side water. The clay sealant did not alter photosynthesis or respiration when 

 placed in the small sealed container with coral, and was thus considered inert 

 as far as these measurements were concerned. 



Each vessel was equipped with two ports, each with an attached lOcc glass 

 syringe. Mixing was accomplished by pushing water back and forth between the 

 syringes via the coral vessel. After mixing (4 cycles), one syringe was 

 removed and the contents were passed through a small curvette containing an oxy- 

 gen electrode. The leads from the oxygen electrode assembly passed into the 

 TEKTITE II habitat and the meter readout was positioned in the window of the 

 wet lab. This arrangement allowed an aquanaut to inject oxygen samples into 

 the electrode curvette and read the meter through the window. Figure 1 contains 

 photographs taken during this operation. 



Measurements were made at time intervals from 15 minutes to 3 hours, and the 

 rates of photosynthesis or respiration were calculated from the slope of the 

 oxygen pressure vs. time curve. Light intensity measurements were made at the 

 same time with a submarine photometer. To determine whether diurnal patterns 

 of dark respiration existed, measurements of respiratory rates were made at 

 various times of the day and night with the coral containers covered with a 

 black opaque plastic sheet. 



RESULTS 



Figure 2 is a plot of relative rates of oxygen production or consumption by 

 Acropora cervicornis as a function of time of day. Integration of the curves 

 above or below the compensation line (zero rate line on the graph) gives a 

 value of net oxygen production or consumption for the 24-hour period. The ratio 

 of oxygen production to consumption may be considered as the photosynthetic 

 potential of the coral-algal association, and used as a maximum value for the 

 possible contribution of algal photosynthesates to the carbon budget of the 

 corals. ■'■ These values are tabulated in Table 1 for several species studied. 

 Table 2 contains the ratios of the maximum observed rate of photosynthesis to 

 respiration. The data in Figure 2 also show that respiration during artifici- 

 ally imposed darkness during daylight does not differ significantly from that 

 during night. This was true of all species studied. 



Refer to the basic equation of photosynthesis relating carbon to oxygen: 

 6CO2+6H2O > Cg H]^2 Og + 6 O2 



VI-240 



