Change of coral carbon metabolism influenced by coral bleaching

Abstract

Organic carbon production (photosynthesis-respiration) and inorganic carbon production (calcification-dissolution) of two massive scleractinian corals, Favites sp. and Porites sp., were measured in a mesocosm, at the early and late stages of the 1998 coral bleaching event. Air-sea CO₂ flux was also measured directly on the surface of seawater, and carbon budgets were calculated from these measurements.
Net organic carbon production was 15.8mmol C m^-2 d^-1 at the early stage of coral bleaching and decreased to 9.5mmol C m^-2 d^-1 at the late stage of coral bleaching. Net inorganic carbon production also decreased drastically from 11.2mmol C m^-2 d^-1 at the early stage to -7.0mmol C m^-2 d^-1 at the late stage of coral bleaching, which was caused by the decrease in calcification in the daytime and increase in the dissolution of carbonate at night. Air-sea CO₂ fluxes were -1.8mmol m^-2 d^-1 at the early stage and -1.1mmol m^-2 d^-1 at the late stage, respectively, which indicates absorption of CO₂ from air to seawater.
The gross primary production/respiration ratio (=1.2) at the early and late stages of bleaching was nearly constant, which suggested that the biological activity of zooxanthellae does not alter significantly at the late stage of coral bleaching. The calcification rate was remarkably reduced compared to photosynthesis. Coral bleaching severely damaged on the physiological activities of corals, and had a large effect on the carbon metabolism in coral-algal symbiosis.