MEPS 271:159-166 (2004)  -  doi:10.3354/meps271159

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.

KEY WORDS: Corals · Mass spawning · Permeable sediments · Sedimentary oxygen consumption · SOC · Coral reefs · Recycling