Hermaphroditic spawning by the gonochoric pillar coral Dendrogyra cylindrus

Scleractinian corals typically reproduce sexually as either gonochoric (separate male and female) or hermaphroditic (producing both eggs and sperm) colonies. The Caribbean pillar coral Dendrogyra cylindrus has been classified as gonochoric, but multi-year spawning observations at a Florida Keys site revealed incidences of hermaphroditism. Separate clonal colonies (ramets) of a single genet released either male or female gametes. Furthermore, 22% of observed ramets produced both eggs and sperm within different regions of a single colony. Over multiple years, one ramet switched from female to hermaphrodite, one from male to hermaphrodite, and one from hermaphrodite to male. Proposed evolutionary mechanisms include size- or age-based energy allocation, environmental energy allocation, or chemically induced change in a single-sex region. Because of the low population density of D. cylindrus in the Florida Keys, sexual partners are scarce, and hermaphroditism may be a strategy to yield higher rates of successful sexual reproduction. The findings also have implications for future restoration efforts aiming to strategically outplant individuals to maximize in situ fertilization.