In addition, there was a significant impact of CO2 on LEDR per cm2 of coral skeleton, and dark respiration and LEDR per µg Chlorophyll c2. Crawley et al. (2010) observed an increase in LEDR per symbiont cell with increasing CO2, whilst dark respiration remained constant. In higher plants, increases in LEDR but not dark respiration may be due to increased levels of carbon fixed by the Calvin cycle, and not to increases in chlororespiration, photorespiration or the water-water cycle (Reddy et al. 1991 and Parys and Jastrz, 2006 cited in (Crawley et al., 2010)). Hence, the increased availability of carbon dioxide may be enhancing the amount of carbon fixed by the Calvin cycle. Our measurements of photosynthesis may not have picked up this increased production of end-products as we measured oxygen evolution rather than carbon fixation.