XVI International Botanical Congess

High rate calcification in coral reefs is light dependent. Proton pumping by calcifying cell membranes, bicarbonate neutralization, the production of CO2 and removal by algal symbionts and free-living algae is responsible for most calcification. With dense algal turfs the most predictable subcommunity, coral reefs have high primary production rates supported by bicarbonate-derived CO2. Nutrient supply is largely provided by cyanophytes, a flexibility in algal requirements and proton-driven uptake from overflowing oligotrophic waters. With a biodiversity likely exceeding three million species in 43 phyla, tropical reefs in their most vigorous form are dependent upon rapid calcification and continued oligotrophic status. Global eutrophication, along with other disturbances, leads to a phase shift to large macroalgae, and a loss of calcification and biodiversity.