Fused embryos and pre-metamorphic conjoined larvae in a broadcast spawning reef coral

Abstract

Fusion of embryos or larvae prior to metamorphosis is rarely known to date in colonial marine organisms. Here, we observed for the first time the embryos of the broadcast spawning coral Platygyra daedalea could fuse during blastulation and further develop into conjoined larvae, and the settlement of conjoined larvae immediately resulted in inborn juvenile colonies. Considering the frequent record of synchronous spawning events and spawn slicks in the field, fusion of embryos might be a naturally occurring phenomenon, and act as an adaptive strategy to form pre-metamorphic united larvae and larger recruits, thereby promoting early survival. However, whether fusion of embryos is common in spawning corals and its implications deserve further investigation.