How science is delivering millions of healthy coral babies onto damaged reefs

Published 8 November 2020
Scuba diver emerging from the ocean surrounded by coral reef Professor Peter Harrison surrounded by corals (credit Great Barrier Reef Foundation).

It has been described as the biggest orgasm in the world. A spectacular natural phenomenon of corals spawning in a massive and coordinated frenzy, much like a giant underwater fireworks display.

Spawning of a branching coral underneath the water
The particles floating above this branching coral are its microscopic eggs and sperm, released when the species spawns (credit Peter Harrison).

Incredibly, coral spawns only once a year, usually in late October or early November. For years, not a lot was known about the sexual reproduction of coral. Some thought that fertilisation happened within the coral, with fully formed coral babies being released, continually rejuvenating through this efficient self-fertilising process.

Yet in 1981 a small group of curious marine biology PhD students – among them Peter Harrison – discovered otherwise. While diving by torchlight on the Great Barrier Reef one night after a full moon in late October of that year, they watched in wonder at the most amazing sight: an ‘underwater snowstorm’ of millions and millions of microscopic eggs and sperm that filled the water in a mass mating ritual.

The Great Barrier Reef is the largest living thing on Earth, with rich corals spanning an area visible from space. But its rich coral beds are under increasing pressure from warmer water, severe cyclones, coral bleaching and poor water quality from run-off. If cyclones become more severe and regular, and the bleaching more frequent, the coral reefs will have less time to rejuvenate between each event.

However, in a world-first, the Great Barrier Reef Foundation and its partners – including Southern Cross University – have successfully pioneered a technique dubbed ‘coral IVF’ or larval reseeding. It is the first project of its kind to re-establish a population of juvenile corals from larvae settling directly on the reef in the hope the coral withstands the increasing threats to the reef.

The coral IVF program is one of more than 60 projects being delivered by the Foundation who immediately saw the potential of this game-changing technique and, with its research partners, now aims to accelerate the regrowth of corals and deliver new life to the reef.

Southern Cross University’s partnership with the Foundation has enabled Professor Peter Harrison, who witnessed that ‘sex on the reef’ mass spawning event 39 years ago, and his team to perfect this innovative technology.

“I was part of the team that discovered the annual mass coral spawning and I can only describe this magical event as an underwater snowstorm with millions of tiny coral eggs and billions of sperm being released into the water,” Professor Harrison says.

“I had the idea to capture the spawn that would otherwise drift away and end up as fish food or disintegrate without fertilising the dying reefs.

“We collect spawn from heat-tolerant corals that have survived bleaching, and rear millions of baby corals in specially designed tanks and coral nursery pools on the reef before delivering them onto target areas of damaged reefs to restore and repopulate them.”

Divers use fine mesh nets to capture the microscopic eggs and sperm that float to the surface.

The spawn is then placed in floating enclosures where they grow for up to a week before reseeding the baby corals (larvae) onto damaged reefs.

Pool structure in the ocean containing coral spawn

The specially designed larval pool, designed by Professor Harrison, that captures the coral spawn (credit Juergen Freund)


“The baby corals settle onto those reefs and in a few years they will grow to the size of dinner plates and beyond, at which point they’ll sexually reproduce and create their own coral babies – re-establishing the breeding populations on damaged reefs,” Professor Harrison says.

The research builds on the enormous success of Professor Harrison’s earlier work in the Philippines, restoring hectares of coral reefs degraded by dynamite fishing. He has been working there since 2012 and research has shown that re-seeded corals can grow into “dinner plate-sized adult colonies within three years and they were able to sexually reproduce”.

There is great promise in the mass larval restoration approach as it has the potential to make a difference to reef recovery on a global scale. The success of this research shows that coral populations where the natural supply of coral larvae has been compromised and damaged can be restored and repaired.

In another world first, robots are giving nature a helping hand by playing ‘stork” and delivering coral babies onto damaged reefs as part of the coral IVF technique. Known as LarvalBots, they are loaded with the coral larvae and cruise just above the reef, spitting out the baby coral directly onto the targeted areas.

Working in partnership with the Foundation, Queensland University of Technology’s Professor Matt Dunbabin says that the LarvalBot invention has been phenomenally successful.

“By thinking out of the box we’ve been able to combine coral ecology and robot technology to give nature a helping hand,” Professor Dunbabin says, explaining how a trial this year re-seeded an area of 3-hectares in just six hours.

“We’re also expanding the LarvalBot fleet as there’s been significant interest from around the world to use them to spread coral larvae where it’s most needed.

“We’ve also designed a new LarvalBoat inflatable system so in the future the bots can be fitted in backpacks and the two can be transported and used together.”

However, Professor Harrison and the Foundation continue to work on more cost-effective methods to help scale up the technology.

“We’re now looking into how we can partner with tourism and private vessel operators, acting as citizen scientists, to collect larvae and release them back onto the reef, to enable us to deploy this restoration technique across many more reef sites,” Professor Harrison says.

While coral IVF has been hailed a success “it is just one technique that is being investigated as part of the world’s largest coral reefs program”, explains Dr Cedric Robillot, Great Barrier Reef Foundation executive director of the Reef Restoration and Adaptation Program.

“The success of this innovation gives us hope for the future as it gives us a method of restoring priority reefs by re-establishing their breeding populations.”

For Great Barrier Reef Foundation managing director Anna Marsden, saving the reef is a huge task but “we’re already making an impact, and it is innovations such as coral IVF that give us hope.

“It truly is inspirational and proves what can be achieved by bringing people and science together to save our irreplaceable reef and its marine life,” Ms Marsen says.


By Anne-Maree Gale for the Great Barrier Reef Foundation. Article published in The Weekend Australian magazine, Nov 7-8 2020

Media contact: Sharlene King, media office at Southern Cross University +61 429 661 349 or