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Date released
26 June 2025

In the early 1980s, Peter Harrison, then a young PhD student at James Cook University, was among a small group of PhD students who first discovered the mass spawning of coral on Australia’s Great Barrier Reef.  

Peter was the lead author of a paper, published in the prestigious journal Science, that described the phenomenon of many coral species spawning in mass, synchronised events. This transformed marine science’s understanding of coral reproduction, which is essential for coral and reef recovery. It also set in train a research career that has become important to the future of coral reefs around the world. 

Just months after the spawning discovery, the Great Barrier Reef suffered its first known mass bleaching event. This kind of climate change impact has become progressively more frequent and more extreme, and has killed vast tracts of coral globally. The loss of coral reefs threatens the livelihoods of more than 300 million people worldwide who rely on them for food, income and coastal protection.  

Today, Professor Harrison’s work is recognised internationally as developing the most viable approach for larger-scale reef recovery to date. He leads continuing research as the founding Director of the Marine Ecology Research Centre at Southern Cross University. 

However, this crucial research almost never happened. Professor Harrison spent 20 years working on coral breeding and re-establishment techniques while trying to secure funding to test his theories on a sufficiently large scale – until his work came to the attention of ACIAR. 

Two men inspecting something under a microscope
Professor Peter Harrison (rear) and Dr Dexter dela Cruz at Australia’s Lizard Island Research Station. Photo: Southern Cross University

Risk and reward 

ACIAR Research Program Manager, Fisheries, Dr Chris Barlow, who oversaw ACIAR’s initial support for the reef restoration projects led by Professor Harrison, describes the past 2 decades as an instructive example of doggedness, and of classic science risk and return.  

‘In this case, high risk but potentially high returns,’ said Dr Barlow. ‘Peter’s concepts hadn’t been tried or tested at all in 2010. Some eminent reef scientists were sceptical. ACIAR knew this, but also recognised Peter’s high standing as a scientist. Because of the importance of coral reefs, we decided to take a risk, accepting also that it required a long-term commitment. 

And it has paid off enormously. The initial ACIAR-supported research in the Philippines is now flowing back directly to Australia, where it is being tested as a management option for the Great Barrier Reef.

The support for Professor Harrison’s work proved to be the start of an enduring relationship and a turning point for applying coral spawning research to larger-scale restoration of damaged reefs.

‘The initial ACIAR project supported the first test of my ideas in 2012, working with colleagues at the Bolinao Marine Laboratory, which is part of the University of the Philippines,’ said Professor Harrison. ‘That’s where I also met an impressive master’s graduate, Dexter dela Cruz.’ 

Professor Harrison invited Dr dela Cruz to do his PhD at Southern Cross University, a decision ACIAR supported by offering the young researcher a John Allwright Fellowship. Dr dela Cruz has since been recognised as Southern Cross University’s International Alumnus of the Year for 2024.

Scuba diver above coral with outstretched arms
Professor Peter Harrison diving on coral reefs in the Philippines. Photo: Dexter dela Cruz
2 scuba divers under the water inspecting coral
Professor Peter Harrison with 4-year-old corals grown from larvae at Heron Island lagoon in 2020. Photo: Southern Cross University

Larval-based restoration  

Dr dela Cruz’s PhD research included experiments to test Professor Harrison’s concepts for larval-based restoration. Initial trials involved culturing coral larvae in the laboratory and then releasing them onto degraded reefs. It wasn’t long before this work started bearing fruit.  

Within 3 years, larval restoration trials restored corals that were able to breed and complete the full coral life cycle. Microscopic sperm and eggs collected after a spawning event were cultured to larval stage in the laboratory, then settled onto highly degraded reef areas where they successfully grew to juvenile and breeding adult stages to sustain a natural reproduction cycle. 

Professor Harrison has since expanded the research to produce innovative methods and insights that enable much larger-scale mass larval culture directly on reefs. In particular, he and his team have made their processes portable, no longer requiring a laboratory. This means Professor Harrison can expand the impact of his work. 

He has now trained and equipped local communities in many regions of the Philippines, Australia and the Maldives. Local partners can now undertake mass coral larval rearing and settlement to catalyse recovery of their damaged reef areas. After 2 to 3 years, those communities are seeing restored corals dominating formerly degraded reef areas and an increased abundance of fish as coral habitats are restored. 

Pools of hope 

The reef-based larval restoration method involves collecting coral spawn using surface skimmers, spawn cones or larger-scale spawn catcher nets, during the natural coral spawning cycles on a healthy reef. The spawn from many corals is carefully transferred into a large container for 1 to 2 hours to facilitate cross-fertilising and increased genetic diversity. The fertilised embryos are then transferred into floating culture pools. These are inflatable 4x4-metre pontoons that support fine-mesh underwater enclosures in which the coral larvae develop.  

Inflatable square on top of water
Mobile inflatable larval rearing pools enable local communities to gather coral spawn to grow millions of larvae to help restore their own reefs. Photo: Peter Harrison

When larvae are ready to settle (after 4 to 6 days of development), the pools are floated over the top of a degraded section of reef and the larvae released down a pipe to settle and develop into new coral colonies. Some larvae are also settled onto dead coral or limestone tiles in the larval pools before transfer to the reef. 

The larval pools and net systems developed by Professor Harrison have reared hundreds of millions of embryos and larvae. The systems are now being rolled out as a knowledge-transfer program for reef communities in Australia, the Philippines and the Maldives, and new work is planned in Indonesia. A wide range of local community stakeholders, and some tourism operators whose businesses are based on coral reefs, have also joined the program. 

Professor Harrison said this ‘scaling up’ of the program has become even more crucial in recent years as bleaching and marine heatwaves become more extreme. ‘Mass bleaching events in 2023 and 2024 were two of the worst years yet, so we really are in a race against time to scale up restoration while improving effective global action on climate change before it becomes too late.’ 

Scuba diver inspecting a coral reef
Professor Peter Harrison diving on the Great Barrier Reef, which is benefiting from ACIAR-supported coral restoration research. Photo: Juergen Freund

Long-term commitment 

Today, Profession Harrison can still be found in scuba gear, working on a reef, the early decades of frustration just memories in the wake of his determination. His crucial alliance with ACIAR and extensive collaborations and partnerships have provided a path to pass the baton of coral restoration to the next generation of young and passionate scientists. 

The long-hoped-for reward for scientists and for ACIAR will be the health and survival of coral reef ecosystems, protecting the millions of people who rely on reefs for their livelihoods. 

ACIAR Projects: ‘Restoring damaged coral reefs using mass coral larval reseeding’ (FIS/2014/063); ‘Regional coral restoration networks and appropriate technologies for larger-scale coral and fish habitat restoration in the Philippines and Australia’ (FIS/2019/123) 

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