Carbon dioxide flux and metabolic processes of a coral reef, Okinawa

This study investigates carbon dioxide flux associated with calcification, photosynthesis and respiration on a coral reef atoll near Okinawa, Japan. M etabolic activity and nutrient concentrations were routinely measured at th ree study sites: (1) on the reef flat, (2) in the lagoon, and(3) 10-50 m of f the reef. Sampling was undertaken during low spring tide events, when the atoll was temporarily emerged, over five periods in 1993-95. Two of the fi ve sampling periods included both day and night sampling. Alkalinity, Disso lved Inorganic Carbon (DIC), Dissolved Oxygen (DO) and pH varied slightly a mong sampling periods, however there were no differences in the range of va riation. Compared to the lagoon and open waters, the reef flat had signific antly lower alkalinity and DIG, and significantly higher DO and pH during t he day. Delta DIC reached a maximum shortly before sunrise and was closely coupled with total alkalinity over the diel cycle. Rates of net organic car bon production and calcification for the reef flat were estimated at 12 mmo l m(-2) h(-1) and 9 mmol m(-2) h(-1), respectively, although calcification was low (i.e., under the detection limit) at night. The respiration rate of the reef flat was approximately 6 mmol m(-2) h(-1). A comparison of CO2 re leased by calcification and net organic production indicates that this reef flat acted as a sink for atmospheric carbon dioxide in the daytime, but ac ted as a source at night, and that the net CO2 diel budget was almost equal ly balanced.