Algal food supply and grazer demand in a very productive coral-reef zone

Abstract

Benthic algal-community net primary productivity (NPP) and herbivore ingestion rates were quantified for the productive zone dominated by the aggressive surgeonfish Acanthurus lineatus (Linnaeus) on the windward crest of Davies Reef, Great Barrier Reef, northeastern Australia. The aim was to evaluate whether or not food supply could be a limiting factor for grazers. Grazing accounted for 65° o of NPP in carbon terms during summer, and 43° o in winter. The most important grazers were the resident territorial surgeonfish Acanthurus lineatus (41° o of NPP in summer) and damselfish Stegastes apicalis (De Vis) (15° o). Grazing rates increased 1.8-times, while NPP increased only 1.2-times, between winter (mean ambient temperatures 23°C) and summer (28°C), but in both summer and winter grazing was significantly less than NPP. NPP which was not accounted for by grazing may have been lost through secretion of dissolved organic matter by algae, export of algal fragments from the zone and decomposition in situ, processes which have been little studied.