Abstract Summary
Scleractinian corals secrete calcium carbonate skeleton to form the solid foundation of the reef matrix. This process of calcification both captures (at geological time scales) and releases (at annual time scales) CO2 at a rate of 0.6 moles for each mole of CaCO3 deposited. Due to the small amount of carbon released, reefs are not included in blue carbon calculations, however, reefs have high rates of primary production, and it is likely that the carbon released by calcification is consumed in other biological processes on the reef, such as photosynthesis by associated macrophytes, and is stored within the reef system. Corals also contribute to the ocean carbon cycle through photosynthesis and respiration. They recycle their nutrients efficiently, so that carbon sequestered into the coral reef stays within the reef system, and organic matter is converted to inorganic carbon stores in coral skeletons and reef sediments. Reef crevices house organic debris, with high organic carbon content, and herbivores produce faecal pellets which sift down into long-term sediments where the carbon processed from algal tissues can be stored for millennia. Loss of hard coral results in the large-scale release of long-term carbon stores. The cycling of carbon on reefs is more complex than that of other shallow coastal ecosystems and their actual role as blue carbon repositories has not been clarified. The balance between organic carbon release and storage on modern coral reefs has not been assessed. This study evaluates the key functional groups for carbon sequestration and storage on Caribbean reefs, and measures their physiological processes to calculate a 'carbon budget' for degraded reefs vs. high-coral cover reefs. Using water sampling and in-situ incubation to measure metabolic rates of reef organisms, we demonstrate the amount of carbon captured within a small area of reef, and by sampling at degraded areas of reef we can project how this will change under future climate conditions. Demonstration of the carbon storage properties of healthy reefs will support restoration of critical reef habitat and structure, and guide protection measures as part of the Blue Carbon Initiative regulations.
