BENO,, C.; GILCHRIST,, S.L.; New College of Florida; New College of Florida: Contributions to the carbonate budget of reef building corals: dissolved organic matter and CO₂

Ecological interaction between corals and the oceanic environment have been suggested to be fundamental in global climate change. Carbon dioxide levels have been associated with global warming and the greenhouse effect. This �greenhouse gas� is naturally stored in calcium carbonate formations and released with the death of coral reef communities but excess CO₂ and lowered pH inhibits coral growth. Corals and other calcifying reef organisms metabolize carbon in two ways: organic carbon production and consumption, or CaCO₃ deposition. The role of dissolved organic matter (DOM) in coral nutrition has not been extensively considered heretofore regarding the oceanic carbon cycle. We decided to investigate whether DOM would influence CaCO₃ deposition and therefore supplement the endosymbiotic contribution to the coral energy budget and promote skeletal structure. Because CO₂ is produced by deposition of CaCO₃, we used this as a measure of growth. Measured carbon flux on the reefs of Roatan, Bay Islands, Honduras revealed significant contribution of DOM in the metabolism of Massive Starlet Coral (Siderastrea siderea) and Boulder Brain Coral (Colpophyllia natans) and greater coral growth was associated with elevated DOM usage. Results suggest that organic carbon flux, calcification and gas exchange can provide valid measures of coral growth and that higher DOM levels could contribute significantly to CaCO₃ deposition and metabolism. Further work in this area may facilitate improvement of oceanic-atmospheric interaction models.