Corals grown in an offshore “coral nursery” at Fitzroy Island on the Great Barrier Reef have spawned for the first time, four years after being planted. A team at the Reef Restoration Foundation has observed Acropora corals, each about 1 metre in diameter, spawning at the island’s Welcome Bay nursery site. Foundation marine biologists and volunteers grew several species of branching and bushy corals on underwater frames that were then planted in patches of bare reef in 2018. Coral spawning is an annual event: multiple species synchronously release sperm and eggs en masse. On the Great Barrier Reef, billions of bundles float to the surface, fertilise and develop into larvae that form new coral colonies when they settle. Sign up for Guardian Australia’s free morning and afternoon email newsletters for your daily news roundup Azri Saparwan, a marine biologist at RRF, described the spawning as “a beautiful milestone” that was contributing to the recovery of corals. The Fitzroy Island corals were grown from fragments that had survived a mass bleaching event, with the hope that they would be resilient to marine heatwaves in future. “We always know climate change is the biggest threat,” Saparwan said. The 2022 mass bleaching event was the first to ever occur during a cooler La Niña year, which had been hoped to provide a recovery period for corals. It was the sixth in recorded history and the fourth mass bleaching event since 2016. A major challenge to reef restoration is the small scales they work on. Some experts estimate that improving coral cover on the Great Barrier Reef by just 1% would require growing 250m large corals. The RRF has established 33 coral nurseries, each of about 100 corals, Saparwan said. “Even if you plant one or two million corals, that would not be as much as what the Great Barrier Reef can hold,” he acknowledged. The reef, which is roughly the size of Italy, consists of more than 3,000 individual reefs. “Reef restoration is not a panacea for greater effort to mitigate the effects of climate change and carbon emissions. That should be the first thing we should be looking at,” said Nathan Cook, a marine scientist at Reef Ecologic. But Cook said restoration projects could “make a difference in small localised scales”, and likely assisted the health of the reef at places where they operate. Bleaching events over the previous six years hopefully served to “test the corals that they are trying to grow and reproduce, and … enable researchers from the Reef Restoration Foundation to be able to naturally select those that are more resilient”, Cook said. The foundation is largely a community effort, with support from about 50 volunteers including divers working in the tourism industry. “These community-based projects do help people to connect to environments that they maybe don’t have a close connection to [otherwise],” Cook said. The Great Barrier Reef Marine Park Authority granted a permit in 2017 for the pilot offshore nursery at Fitzroy Island to go ahead.