‘A beautiful milestone’: coral grown in Great Barrier Reef nursery spawns for first time

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.

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.