Ciliary propulsion and metachronal coordination in reef coral larvae

Larval dispersal is critical to the survival of coral reefs. As the only motile stage of the reproductive cycle, coral larvae choose a suitable location to settle and mature into adult corals. Here, we present the first detailed study of ciliary propulsion in the common stony reef coral Acropora millepora . Using high-speed, high-resolution imaging, particle image velocimetry, and electron microscopy, we reveal the arrangement of the densely packed cilia over the larval body surface, and their organisation into diaplectic (transversely propagating) metachronal waves. We resolve the individual-cilium’s beat dynamics and compare the resultant flows with a computational model of a ciliary array, and show that this form of ciliary metachronism leads to near-maximal pumping efficiency.