Rapid egg transport following coral mass spawning at Ningaloo Reef, Western Australia

During mass spawning of tropical corals, extremely dense accumulations of eggs develop throughout the water column, the fate of which depends on physical conditions, such as topography, currents, and prevailing winds. We measured egg transport [mainly acroporid corals and the palolo worm, Eunice viridis (Gray, 1847)] during a mass spawning at Ningaloo Reef, Western Australia, in April 2010. We tracked changes in egg and embryo abundance in the lagoon over five consecutive days with plankton tows at the sea surface immediately after spawning and four and 16 hours later, and characterized the flow regime with drifter deployments. Egg dispersal was rapid with a pronounced decrease in concentration within four hours of spawning, from approximately 10⁶ to 10¹ and 10⁴ m^-3 for corals and E. viridis, respectively, on the peak date; few eggs or embryos remained within the lagoon after 16 hrs. Changes in concentration of eggs and embryos along transects inside the lagoon and perpendicular to the reef flat reflected the local hydrodynamics and high flushing rate, providing empirical support for a biophysical model from the same site.