Optimization of a spawning‑induction protocol for the prediction of natural coral spawning

Abstract

Many scleractinian corals only spawn once a year, so opportunities for collecting their gametes are limited. Consequently, the induction of spawning in coral would be useful, not only for studies on the mechanisms of coral reproduction, but also for stock enhancement. A spawning-induction method using hydrogen peroxide (H₂O₂) has already been developed for coral, but most adult corals died after exposure to H₂O₂. In the present study, a comparison of the effects of low concentrations of H₂O₂ (0.5–1.5 mM) on adult corals indicated that 1 mM H₂O₂ was the upper threshold for inducing spawning without harmful effects. In addition, the effect of repeated exposure to H₂O₂ on the same colony, and the relationship between the timing of H₂O₂ exposure and the lunar phase, were investigated. The success rate of induced spawning was dependent not on H₂O₂ concentration but largely on the time lag between exposure to H₂O₂ and timing of natural mass spawning. Spawning was induced in ≥ 70% of coral colonies when they were exposed to H₂O₂ within the 2-day period prior to a natural mass spawning event. The described technique is not only useful for the collection of artificially induced coral gametes, but also for estimating the specific timing of natural mass spawning of coral.