In-situ spawning of the studied species. (A) At ~30 minutes prior to spawning, Acropora eurystoma colonies can be observed in a 'setting' mode, in which egg-sperm bundles are already visible at the mouth-opening of each polyp. (B) Synchronized whole-colony spawning of A. eurystoma. (C) Partial spawning of Platygyra lamellina without the formation of egg-sperm bundles, in contrast to (D) Synchronized whole-colony spawning of egg-sperm bundles by P. lamellina. (E) Acanthastrea echinata spawning and (F) a male Galaxea fascicularis colony. Scale bars indicate ~1 cm.