Controlled out-of-season spawning of reef-forming corals using offset environmental cues

The global climate crisis has heightened the urgency for developing interventions to enhance resilience and recovery of coral reef ecosystems. However, research programs are often bottlenecked by availability of coral early life stage material due to the annual nature of coral mass spawning. We present a proof-of-concept of “out-of-season” spawning, utilising aquarium control technology to induce spawning in multiple Great Barrier Reef (GBR) corals held in long-term indoor aquaria. By applying a 6-month offset environmental profile encompassing seasonal temperature, photoperiod, and lunar cues, we induced synchronised coral spawning during austral autumn/winter between 2022-2023. We also “phase-shifted” the hour of sunset by four hours on spawning nights, creating a more favourable time window (i.e., minimising late nights) for gamete fertilisation. Spawning occurred on comparable nights after full moon (NAFM) and at similar times after sunset (TAS) to wild conspecifics, with 2023 cohorts showing the closest alignment. Gamete fertilisation was successful for six species: Acropora millepora, Acropora loripes, Acropora hyacinthus, Acropora elseyi, Acropora austera, and Montipora aequituberculata producing ~1.8 million larvae. We outline physiological insights into environmental regulation of coral spawning synchronicity and discuss the potential for out-of-season spawning to accelerate coral research and enhance reef restoration programs.