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 programmes are often bottlenecked by availability of coral early life stage material owing to the annual nature of coral mass spawning. We present a proof-of-concept of 'out-of-season' spawning, utilizing aquarium control technology to induce spawning in multiple Great Barrier Reef (GBR) corals held in long-term indoor aquaria. By applying a six-month offset environmental profile encompassing seasonal temperature, photoperiod and lunar cues, we induced synchronized coral spawning during austral autumn/winter between 2022 and 2023. We also 'phase-shifted' the hour of sunset by four hours on spawning nights, creating a more favourable time window (i.e. minimizing late nights) for gamete fertilization. Spawning occurred on comparable nights after full moon (NAFM) and at similar times after sunset (TAS) to wild conspecifics, with 2023 cohorts showing the closer alignment. Gamete fertilization was successful for six species: Acropora millepora, Acropora loripes, Acropora hyacinthus, Acropora elseyi, Acropora austera, and Montipora aequituberculata, producing ca 2 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 programmes.