Coral gardeners regrow 12 hectares of reef off a Pacific atoll

A six-year effort to rebuild a damaged coral reef off the Pacific atoll of Tavua has restored around 12 hectares of living reef, according to a report by the scientists and local divers behind the project. The team says fish numbers on the replanted sections are now close to those on undamaged reefs nearby, a sign that the restored areas are working as habitat rather than simply looking green.

The reef was badly affected by a period of unusually warm water and a cyclone in the same year, which together killed much of the branching coral on the atoll's sheltered side. The Tavua Reef Institute, a small research station run with the atoll's community council, began growing coral fragments on underwater frames shortly afterwards.

A nursery under the sea

Pieces of healthy coral are hung on rope lines and metal trees in a nursery in calm water, where they grow quickly for around a year. Divers then attach them to the reef with marine cement or cable ties. More than 90,000 fragments have been planted so far, most of them by a team of 30 local divers trained by the institute.

Dr Sigrid Ellefsen, a marine ecologist who has led the monitoring, said survival rates had improved as the team learned which corals did best where. "In the first year we lost almost half of what we planted," she said. "Now survival is above 80 per cent, because we choose fragments from colonies that came through the heatwave."

We are not just replanting a reef. We are trying to plant one that can cope with the water it will live in.

The project is small compared with the scale of the threat. Restoration costs around €40,000 per hectare, and scientists stress that planting cannot replace action on rising sea temperatures. But Owen Mbeki, who chairs the atoll's community council, said the reef was the island's main source of food and protection from waves, and that young people now saw a future in caring for it.

The institute is sharing its methods with three neighbouring islands, and a group of researchers from the Wrenhaven Marine Institute is due to spend a month at the station next year to study how the restored reef recovers after storms.