Effect of Elevated Carbon Dioxide on Two Scleractinian Corals: Porites cylindrica (Dana, 1846) and Galaxea fascicularis (Linnaeus, 1767)

Abstract

This study reveals the effect of elevated p CO 2 on Porites cylindrica and Galaxea fascicularis . The corals responded differently under elevated p CO 2 . Zooxanthellae cell density, cell mitotic index, and photosynthesis rate of P. cylindrica decreased drastically under the elevated p CO 2 . At the end of the experiment, P. cylindrica suffered from a declining calcium carbonate precipitation rate. G. fascicularis increased its respiration rate and expelled 71% of its symbiotic zooxanthellae algae under elevated p CO 2 . Photosynthetic pigments in the remaining zooxanthellae algae increased from 1.85 to 11.5 times to sustain its photosynthetic outputs. At the end of the experiment, G. fascicularis managed to increase the rate of its calcium carbonate precipitation. Increase p CO 2 in the atmosphere may affect species diversity of coral reefs.