Specimen collection and species identification

The collection of 11 A. digitifera is explained in our previous study [13]. In brief, a branch fragment was collected from each of 11 A. digitifera colonies in Sesoko, Okinawa, Japan. Gametes from four A. tenuis were collected in the field in front of Sesoko Station (Tropical Biosphere Research Center, University of the Ryukyus). Gamete-collecting devices were set above each individual colony, and bundles of gametes were brought to the laboratory and mixed to allow fertilization. Larvae were reared by daily transfer to fresh seawater and maintained at approximately 26 °C. Six larvae of A. tenuis were preserved in RNAlater (Waltham). Species were identified based on morphology by Dr. Kazuhiko Sakai for A. digitifera and by Dr. Masayuki Hatta for A. tenuis. Collections of samples were approved by the Aquaculture Agency of Okinawa Prefecture (permit numbers 28–31 and 27–1).