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Abstract

During the annual synchronous release of gametes by corals, a large amount of energy-rich organic material is released to the reef environment. In November 2001, we studied a minor spawning event at Heron Island in the Great Barrier Reef (GBR), Australia. Laboratory experiments showed that egg release by the staghorn coral Acropora millepora amounted to 19 ± 15 g dry mass (mean ± SE, n = 8) per m2 coral surface. Carbon content reached 60.1 ± 4.0% and nitrogen content 3.6 ± 0.4% of the egg dry mass. During this minor spawning period, Acropora corals from the reef crest released 7 g C and 0.4 g N as eggs m-2 reef. In situ experiments (n = 11) using stirred benthic chamber measurements revealed that the sedimentary O2 consumption (SOC) of the lagoon sediments increased sharply immediately after the coral spawning. Extreme SOC rates of 230 mmol O2 m-2 d-1 were reached 2 d after the event, exceeding the pre-spawning rate by a factor of 2.5. This maximum was followed by a steep decrease in SOC rates that gradually levelled off and reached pre-spawning values 11 d after the event. The immediate and strong response of SOC shows that the coral spawning event provides a strong food impulse to the benthic food chain. Our results demonstrate high decomposition efficiency of permeable carbonate reef sands and underline the role of these sediments as a biocatalytical recycling system in the oligotrophic reef environment.