Sexual reproduction of Hawaiian black corals,with a review of the reproduction of antipatharians (Cnidaria: Anthozoa: Hexacorallia)

Abstract. Black corals (Cnidaria: Antipatharia) are ecologically important members of the sessile invertebrate fauna, but due to their typical deep‐water environments (>50 m), very little is known about their basic biology, including reproduction. We used histological techniques to examine the sexual reproduction of members of eight species of antipatharians collected from the Hawaiian Islands over a wide depth range (10–1327 m). Gametes of all species examined were found in association with the primary transverse mesenteries, which in some cases reached into the cavity of lateral tentacles. Specimens contained either spermatocysts or oocytes, but never both within the same individual, suggesting either a gonochoric or a sequentially hermaphroditic mode of reproduction. No developing embryos or larvae were observed in any of the samples, indicating that fertilization and larval development likely occur externally in the water column and not internally within polyps. We compared our results with previously published information on the sexual reproduction of antipatharians. Our review suggests that in antipatharians, more generally, (1) entire colonies are either female or male (although sequential hermaphroditism cannot be ruled out in most cases and has been reported previously for one species), (2) gametes are confined to the primary transverse mesenteries in most species, and (3) there is no evidence of internal fertilization. Further studies are needed to determine whether gonochorism or sequential hermaphroditism is more prevalent within the Antipatharia, whether dimorphic polyps occur within this taxonomic order, and to examine the reproductive seasonality and larval behavior of individual species.