Spectacular footage provides hope to scientists

Those who have experienced the spawning firsthand say it’s like being in a “reverse snowstorm” where millions of eggs and sperm stream upwards from the coral below.

This year was particularly spectacular.

Great Barrier Reef Legacy director and marine biologist Dr Dean Miller said it was the “best coral spawning event and the most encouraging moment I’ve seen on the Great Barrier Reef since 2016”.

The spawning only happens once a year between October and December and can only be predicted by looking at the phase of the moon, water temperature and the tide.

As Dr Miller explains, “corals are stuck to the bottom of the ocean and they can’t get up to meet other corals”, so they have developed an alternative method to reproduce.

This involves coordinating the timing of the release of eggs and sperm, increasing the chance of them meeting each other at the surface.

“It’s extremely effective — they have created the largest living structure using this method,” Dr Miller told news.com.au.

“I liken it to an underwater blizzard or snowstorm in reverse, everything is coming up from the bottom where the corals are, and floating to the surface,” he said.

“You are surrounded by millions if not billions of individual coral eggs and sperm of all different colours.”

Divers can distinguish the eggs from the sperm as the eggs are generally bigger.

Dr Miller said the event was up there with the “northern and southern lights” as a “very spectacular thing to witness and be part of”.

This year he managed to capture the spawning at the reef north of Port Douglas across three nights, after the full moon in November.

It has been particularly heartening for him to see the mass of activity this year as three coral bleaching events since 2016 have dampened previous events.

Corals are not heavily reproductive after bleaching events due to heat stress so there has not been the same abundance of spawn in previous years. The bleaching also impacts the number of corals that spawn and the diversity of those that do spawn are reduced.

“To have a successful spawning event means the reef is in a state of recovery and repair,” Dr Miller said. “This is how the Great Barrier Reef regenerates.”

While this is a positive moment for the reef Dr Miller said more needed to be done to protect its future.

“We’re certainly not out of the woods in terms of climate impact,” he said.

“This is predicted to be a potential coral bleaching year so we still need to do everything we can to ensure the Great Barrier Reef remains ‘great’ forever.”

This includes action on climate change as well as activities on the ground to ensure the reef’s health and resilience.

Dr Miller said parts of the reef were 1000 years old and this is part of the problem.

“We are asking them to adapt to heat stress within their lifetime,” he said.

The United Nations has warned the world is on track for 2.7C of warming, and even if we are successful in keeping temperature rises down to 2C by around 2050, the world’s coral reefs would virtually be wiped out.

Originally published as Stunning footage of Great Barrier Reef spawning provides hope to scientists