Simultaneous measurement of the gross and net primary production of the benthic community and the net input of organic carbon delivered by currents to the coral reef flat of the north shore of Moorea, French Polynesia, confirms that carbon fixation by bottom-dwelling autotrophs, including algal symbionts in corals and benthic free-living algae, is the major source of new organic matter to this system. However, particulate organic carbon, including plankton, detritus, and macroalgal fragments originating primarily on the fore reef and reef crest and carried onto the reef flat by currents contributes up to 13% of the net organic carbon input to the zone nearest the reef crest. These results are typical of the many reef flats worldwide that experience unidirectional flow.