Induced sexual reproduction ex situ reveals bidirectional sex change of the coral Montastraea cavernosa

Induction of gonad maturation and synchronized spawning of corals ex situ has been mostly used to propagate corals for restoration, but it also provides a unique opportunity to study the reproductive biology of species. We present, for the first time, the induction of gonad maturation and synchronous spawning of the coral Montastraea cavernosa in a laboratory. This was achieved by mimicking the annual temperature, sun and moon cycles experienced in the northern portion of Florida’s Coral Reef. Similarly to field observations, peak spawning of M. cavernosa colonies in the laboratory occurred 5–10 nights after the full moons of July, August, and/or September, 75–125 min after sunset. This coral species was known as gonochoric, meaning colonies are either females (release eggs) or males (release sperm). Yet, three consecutive years observing the same colonies ex situ revealed that these corals are capable of changing sexes annually, and they can do so in both directions. Spawning observations and histology showed corals shifting from male to female, others shifting from female to male, and several changing sex one year and reverting to their original sex in the following year. The sex change was not related to size, nor likely socially driven. A greater number of colonies was observed to shift from female to male when food provision was reduced. Further studies are required to determine if food availability drives sex change in this species.