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

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 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 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.