Australian Scientists Pioneer Larval Regeneration of Damaged Coral Reefs

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Coral spawning in action (Photo: Gary Cranitch / Queensland Museum)

Researchers from Southern Cross University in Queensland, Australia, in partnership with the Great Barrier Reef Foundation, have reported the success of a pioneering project to re-populate the heavily damaged reef using coral larvae grown in tanks after sperm and eggs were collected during mass coral spawning events.

The Great Barrier Reef has been devastated in the past few years by a series of mass bleaching events, caused by rising ocean temperatures in the wake of a particularly stong El Nino weather pattern. Bleaching, which occurs when symbiotic zooxanthellae algae – which provide coral polyps with nutrients and colour – is ejected due to the elevated temperature, can eventually lead to coral death if the temperatures do no return to normal and the algae are not re-acquired.

During the coral spawning of November 2016, lead researcher Professor Peter Harrison and his team collected vast quantities of sperm and eggs ejected during the mass spawning, and used them to grow over a million individual coral larvae, which were then returned to the reef under the protection of mesh tents. Under normal conditions, sperm, eggs and larvae all constitute the diets of a variety of reef fish.

Returning to the reef in November 2017, the team discovered to their delight that the surviving juvenile corals had successfully established themselves on the reef.

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Professor Harrison and a research assistant mixing coral sperm and eggs (Photo: Gary Cranitch / Queensland Museum)

'This is the first project of its kind on the Great Barrier Reef to successfully re-establish a population of juvenile corals from larvae settling directly on the reef,' said Southern Cross University’s Professor Harrison, who co-discovered the mass coral spawning phenomenon known as 'sex on the reef' some 30 years ago. “This pilot study carried out on Heron Island shows that our new techniques to give corals a helping hand to conceive and then settle, develop and grow in their natural environment can work on the Great Barrier Reef,' he said, adding that the research not only applies to the Great Barrier Reef but 'has potential global significance – it shows we can start to restore and repair damaged coral populations where the natural supply of coral larvae has been compromised.'

The project was made possible through a donation to the Great Barrier Reef Foundation from the former chairman of Goldman Sachs, Australia and New Zealand, Stephen Fitzgerald, who is now based in the UK. 'Working with the Great Barrier Reef Foundation board for many years, I’ve seen first-hand what’s been happening with our reef, and reefs around the world, facing such adversity from the impacts of climate change,' said Mr Fitzgerald. 'When I heard about the amazing success Peter was having with his work, I knew I had to help.'

'It’s wonderful to have another tool in the arsenal for our Great Barrier Reef,' said Anna Marsden, managing director of the Great Barrier Reef Foundation. 'We’re increasingly looking to innovations like larval ‘reseeding’ to help coral reefs rebuild and adapt so they can live through everything the world is throwing at them and survive into the future. There is much more to be done but this is definitely a great leap forward for the Reef and for the restoration and repair of reefs worldwide'

Other reef regeneration initiatives around the world have involved 'coral gardening', the process of taking broken coral structures and transferring them to a location where they are more able to grow or, as in the case of the Philippine's Biri Initiative, 'planting' them on man-made structures such as concrete reef buds and iron cages, a process that is both time-consuming and expensive. Although Biri's Project 250 has proved successful, coral gardening has had limited success in other areas.

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One of the mesh tents used to protect the coral larvae in situ from predation (Photo: Gary Cranitch / Queensland Museum)

The new research was not without its challenges, including the need for the careful rearing of coral larval cultures and complex diving operations on the reef by the research team, who worked closely with the Great Barrier Reef Marine Park Authority to implement the ground-breaking project.

'In recent years, the impacts of climate change on the Great Barrier Reef have undoubtedly accelerated, as we saw with back-to-back years of coral bleaching,' said Great Barrier Reef Marine Park Authority chief scientist, Dr David Wachenfeld. 'Innovative science like larval reseeding is one piece of the puzzle of protecting the Reef into the future.'

'The success of these first trials is encouraging,' added Dr Wachenfield. 'The next challenge is to build this into broader scale technology that is going to make a difference to the Reef as a whole.'

Based on the success of the 2016 pilot project, the Australian Government is investing funds to advance Professor Harrison’s larval reseeding research, which include the investigation of techniques to increase the scale of the delivery method to larger areas of affected reefs, and the collection of larger amounts of natural coral spawn.

'With this new funding from the Australian Government and continued support from the Great Barrier Reef Foundation and the Great Barrier Reef Marine Park Authority, our research team used the technique again this month at Heron Island to collect and ‘match-make’ coral spawn, producing mass quantities of coral larvae to deliver new coral ‘babies’ onto the reef,” Professor Harrison said.

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Professor Harrison and his team checking the coral's progress (Photo: Gary Cranitch / Queensland Museum)

The results are encouraging, as studies have shown that following the worldwide bleaching events of 2015 and 2016, 21 of the 29 coral reefs listed as UNESCO World Heritage Sites have been affected. Although there has been a global pause in bleaching events and recovery in some areas, future warming of the oceans may prevent damaged coral from recovering in time, and causing further degradation to the reefs.

The success of the pilot project around Heron Island brings with it 'great promise' in the mass larval restoration approach to coral reef regeneration. It is hoped that using natural coral spawn - which brings with it the potential to generate many millions of larvae from a range of different coral species, will be able to be applied on a much larger scale.

'I’m excited to announce that we’ve already observed successful settlement of the new coral larvae this year – so it’s worked,' said Professor Harrison. 'We’ll be monitoring the growth of both coral colonies and working to further refine the technique for potentially broader application in the future.'






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