Consumption by herbivorous fishes of macroalgae exported from coral reef flat refuges to the reef slope

Much of the production by macroalgae on the broad, sandy reef-flat of the fringing reef of Moku o Loe in Ka-ne'ohe Bay, Oahu, Hawai'i, is transported to the leeward outer reef flat and reef slope areas by wind-driven currents. The export of algae from the inner reef flat can amount to an average delivery rate over a year of 163 g wet weight d(-1) m(-1) of leeward reef crest (2.45 g C d(-1) m(-1)). This export is equivalent to estimates of the production of fixed carbon by grazed turf algae on the hard substratum at the outer edge of the reef. Grazing by herbivorous fishes resident on the reef slope and outer reef flat area can prevent the development of accumulations of this transported macroalgae in these habitats or gradually eliminate accumulations; however, when rates of delivery are high, long-lasting accumulations of macroalgae can develop between and on top of living corals. Broad sandy reef-flats have often been reported to have stands of macroalgae which are not utilized by herbivorous fishes, and the production of these stands may often be transported to other leeward habitats. The reason for the development of herbivore-free refuges for algae could be the relatively low preference herbivores have for macroalgae in comparison with the more nutrient-rich filamentous algal turfs available on the hard surfaces of the outer reef flat and reef slope.