δ¹³C Values in Marine Organisms from the Great Barrier Reef

Abstract

The carbon isotope composition of marine organisms collected on the Great Barrier Reef near Lizard Island, Australia, was determined. Emphasis was placed on photosynthetic organisms including algae, zooxanthellae, angiosperms and symbiotic systems. The photosynthetic organisms had δ¹³C values ranging from -5.1 to -32.40,. Symbiotic systems and non-photosynthetic organisms had δ¹³C values within this range. CO₂ released by acid treatment from coral, shell and cone carbonates had δ¹³C values between + 3.9 and - 2.70,. The results with photosynthetic tissue generally are interpreted in comparison to terrestrial plants as showing a major assimilation of CO₂ into organic compounds via ribulosebisphosphate carboxylase in the marine ecosystem. However, a few photosynthetic organisms exhibited δ¹³C values between - 5.10, and - 110, and could be assimilating CO₂ via phosphoenolpyruvate carboxylase. A unified scheme is presented for the pathway of carbon assimilation in the reef from the sea water through both autotrophic and heterotrophic metabolism, and finally to calcification.