Biogeochemical responses following coral mass spawning on the Great Barrier Reef: pelagic-benthic coupling

This study quantified how the pulse of organic matter from the release of coral gametes triggered a chain of pelagic and benthic processes during an annual mass spawning event on the Australian Great Barrier Reef. Particulate organic matter (POM) concentrations in reef waters increased by threefold to 11-fold the day after spawning and resulted in a stimulation of pelagic oxygen consumption rates that lasted for at least 1 week. Water column microbial communities degraded the organic carbon of gametes of the broadcast-spawning coral Acropora millepora at a rate of > 15% h(-1), which is about three times faster than the degradation rate measured for larvae of the brooding coral Stylophora pistillata. Stable isotope signatures of POM in the water column reflected the fast transfer of organic matter from coral gametes into higher levels of the food chain, and the amount of POM reaching the seafloor immediately increased after coral spawning and then tailed-off in the next 2 weeks. Short-lasting phytoplankton blooms developed within a few days after the spawning event, indicating a prompt recycling of nutrients released through the degradation of spawning products. These data show the profound effects of coral mass spawning on the reef community and demonstrate the tight recycling of nutrients in this oligotrophic ecosystem