Carbon and oxygen isotopic ratios, measured along the growth axis of branches from colonies of the scleractinian coral Acropora formosa collected at 2 and 12 m depth at Yonge Reef (Northern Great Barrier Reef, Australia), were compared to metabolic rates. Measurements of primary production, respiration, temperature and irradiance were carried out in situ twice, in winter and in summer, and skeletal isotopic analyses were performed at 2 reference points corresponding to metabolic measurements. There was no evidence of any relationship between oxygen isotopic ratio and productivity. Skeletal delta13C values and the rates of productivity showed a statistically significant positive relationship as predicted by the model proposed by Goreau (1977a: Proc 3rd Int Coral Reefs Congr 1:395-401); delta13C increased as a function of increasing productivity. The scattering of delta13C observed particularly during summer demonstrates that the relationship between delta13C and primary productivity is not very tight and that other internal and external parameters probably operate to explain the delta13C variability.
Acropora formosa · Productivity · Skeletal delta13C and delta18O
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