It's a sunny day on the pontoon floating above Moore Reef, off the coast of Cairns, and tourists are strapping on snorkels and zipping into wet suits, ready to experience one of the world's natural wonders.

Key points: Marine biologists say this year's coral spawning — in the nights after the full moon in November — released three times more eggs and sperm than last year

Marine biologists say this year's coral spawning — in the nights after the full moon in November — released three times more eggs and sperm than last year Researchers capitalised on this and captured billions of egg and sperm bundles in special floating coral nurseries

Researchers capitalised on this and captured billions of egg and sperm bundles in special floating coral nurseries These nurseries will help 'baby' coral develop before researchers settle the larvae onto the reef — to increase their chance of survival

Few of them may know it but, when night falls, the massive marine ecosystem beneath their neon-flippered feet will become the stage for an event marine scientists dream of.

Colloquially, the annual spawning of coral on the Great Barrier Reef is known as the world's largest orgasm.

"It really feels like you're in the midst of an underwater snow storm, or blizzard," Katie Chartrand, a senior researcher with James Cook University's TropWATER research group, said.

"It's an amazing thing to be able to see."

It's known not only for its surreal beauty, but as a key step in the ongoing survival of the reef — one that takes place over a few nights following an end-of-year moon, as coral regenerates.

Marine biologists at Moore Reef off Cairns say this year's coral spawning released three times more eggs and sperm compared to last year. ( Supplied: Pablo Cogollos, Sunlover Reef Cruises )

But in conjunction with tourism operators and reef conservation group Citizens of the Great Barrier Reef, scientists from three universities are seizing this small window of opportunity.

Their goal is to effectively outpace nature, trying to fast-forward the rate at which the reef reproduces.

"It is suggested that one out of every million coral larvae fully settle into the grown adult colony, so that process is very inefficient naturally by Mother Nature's hands," Ms Chartrand said.

"We're trying to enhance the numbers — rather than letting the winds and currents let these larvae float away … we want to ensure we maximise the number that actually find some degraded areas or open reef area to settle on to."

Spawn kept in coral nurseries

The researchers camped on the pontoon overnight on Sunday, anxiously awaiting the rare night-time spawn.

It's been hailed as a success, with some marine biologists saying they have witnessed three times the volume of eggs and sperm as last year.

Researchers watched as a portion of the billions of egg and sperm bundles moved into columns, then were captured in specialised floating coral nurseries.

"These inflatable pools will hold these bundles as they develop from an early embryo stage into a full-blown coral larvae, which is the initial baby that then will settle back down on the reef in around five or six days," Ms Chartrand explained.

Coral spawns on the outer Great Barrier Reef around two to six nights after the full moon in November. ( Supplied: Gabriel Guzman, Calypso Reef Imagery )

This is the second year the project — sometimes labelled IVF for the reef — has taken place, but this year's project is taking place on a significantly larger scale.

The scientists have also introduced a secret weapon of sorts: a symbiotic algae that, testing has shown, will give the baby corals a much-needed energy boost.

"The reason we need to put algae into these corals is that's what naturally occurs on the reef within the first week of settlement," project leader and coral IVF pioneer Professor Peter Harrison said.

"But many of the coral larvae end up dying during that first period.

"So what we're trying to do is add like a battery pack back into the larvae as soon as possible to increase their energy and therefore increase their survival and growth rates."

Researchers racing against time

In the coming weeks and months, researchers will keep track of the settlement rates of the microscopic larvae.

If successful, their interventions will yield baby coral in about six or nine months' time.

But more broadly, the hope is that the biodiversity of Moore Reef — a source reef, meaning it contributes to the biodiversity of reefs elsewhere — will be reproduced before it and other reefs are damaged by threats, climate change chief among them.

"With the larval restoration project, we're trying to buy time," Professor Harrison said.

Peter Harrison has been researching the Great Barrier Reef for 40 years. ( ABC News: Jesse Thompson )

"We know that increasing climate change impacts are going to occur on the Great Barrier Reef and other reefs all around the world, and every reef system on the planet is losing corals faster than they're naturally replenishing.

"We're getting desperate to intervene to capture the remaining genetic diversity that's in these populations and try to restore corals while we can."