Rapid recycling of coral mass-spawning products in permeable reef sediments

During the annual synchronous release of gametes by corals, a large amount of energyrich 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 m 2 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 O 2 consumption (SOC) of the lagoon sediments increased sharply immediately after the coral spawning.Extreme SOC rates of 230 mmol O 2 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 prespawning 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.