Great Barrier Reef: How a Spectacular Coral Spawning Event Helps Raise Heat Tolerant Corals

Great Barrier Reef: How a Spectacular Coral Spawning Event Helps Raise Heat Tolerant Corals

It’s nearly 10 p.m. and Dr Kate Quigley is still waiting. Using red lights to minimize disturbance to animal behavior, she inspects corals.

Quigley, who studies reef restoration at the Australian Institute of Marine Sciences, looks for “little red dots all over the surface.” A spotty appearance is a hallmark sign that a coral is about to spawn, releasing sperm and eggs in bundles that resemble small bubbles.

Depending on the species, they can be hot pink, purple, or blue. “It’s almost like shaking one of those snow globes,” Quigley says. “You see all the little particles in the water. “

Dr Kate Quigley looking for “little red dots” a sign that a coral is about to spawn. Photography: Marie Roman / AIMS

Quigley works at AIMS ‘National Sea Simulator, a large facility in Townsville where more than 3 million liters of filtered seawater are pumped daily, home to large numbers of coral colonies. At SeaSim, as it’s called, the buzzes are calibrated to specific temperatures and partial pressures of carbon dioxide – the latter for ocean acidification experiments.

The spawning of corals, which takes place en masse once a year, is one of Earth’s great biological spectacles. Quigley compares the scale and magnitude to the annual migrations of mammals in Africa.

From top to bottom of the Great Barrier Reef, for several days after the November Full Moon (this year November 19), several species of corals synchronize the release of their sperm and eggs. In the ocean, billions of these beams float on the surface of the water, fertilize and develop into larvae that eventually settle on the reef and form new colonies of corals.

Researchers hope to breed Great Barrier Reef corals that are more resistant to extreme heat events - video
Researchers hope to breed Great Barrier Reef corals that are more resistant to extreme heat events – video

Corals housed at SeaSim spawn in captivity at the same time as they spawn in the wild. For several consecutive days this week, Quigley and his colleagues worked late into the night, carefully collecting spawning packages for a selective breeding program.

Each breeding coral is kept in its own separate container, so that its bundles can be isolated. Many are housed in outdoor tanks, under moonlight, which is an important signal that triggers the spawning event. For corals kept indoors, the SeaSim has finely calibrated facilities that allow scientists to replicate both the timing and intensity of sunlight and moonlight.

A researcher from the Australian Institute of Marine Science’s coral spawning facility. Photograph: Roslyn Budd / AIMS

“We are now able… to replicate these natural signals that corals would need,” says Quigley. She and her team have only collected hundreds of breeding corals in the past fifteen weeks. Leaving marine invertebrates in their natural environment for as long as possible also maximizes their exposure to spawning signals they would get in the wild, which includes a rapid rise in temperature at this time of year.

Breeding for heat resistance

The Great Barrier Reef is home to over 3,000 individual reefs, a patchwork of marine life about the size of Italy. There is a natural temperature gradient from north to south: the waters in the northern part of the reef, closer to the equator, are warmer.

“These corals [north] are better able, thanks to the exposure they have undergone during their lifetime, to withstand high temperatures, ”explains Quigley. “In the south of the Great Barrier Reef, it’s colder there, so when [corals] affected by a heat wave, they are much more vulnerable.

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Natural differences in heat tolerance form the basis of Quigley’s breeding research. At the end of last year, she developed a machine-learning algorithm that produces GPS coordinates showing where the most heat-resistant corals are found.

Last week, she and her team returned from an expedition to the far north of the Great Barrier Reef, 875 km from SeaSim. Using his algorithm, they collected hundreds of potentially heat-resistant corals, which had survived the high temperatures of the mass bleaching events of 2016, 2017 and 2020.

Researcher collects coral in Wood and Martin Reefs
A researcher collects coral from Wood and Martin Reefs for spawning at the National Sea Simulator. Photography: Marie Roman / AIMS
Broodstock collection in far north Queensland
Collection of broodstock in the far north of Queensland. Photography: Marie Roman / AIMS

After spawning in the SeaSim, scientists will breed the most heat-resistant corals with more vulnerable specimens collected from the southern Great Barrier Reef. The process of mixing spawning is “no different than mixing cocktails in specific proportions,” explains Quigley. “We can control who is the mother and who is the father… we are able to create baby corals that have a mixture of these genes. “

Research speeds up a natural process called gene flow. Research shows that the genetic material of corals, including heat-adaptive genes, propagates naturally through the reef. “There is a movement of genes,” Quigley says. “However, it’s probably going to happen too slowly for the kind of warming we’re getting right now. “

Accelerating the spread of genetic material is one of many techniques being explored to help make the reef more resilient, says Dr Line Bay, who leads the reef recovery, adaptation and restoration team at AIMS.

Corals live in symbiosis with microscopic algae, which play an important role in their growth and survival. “We have several projects examining how these algae affect coral health and whether we can influence… heat tolerance of corals through direct selection of algae,” Bay said.

Climate change “a very important threat”

In the SeaSim, tank temperatures can be increased to test how well corals – either those that are selectively bred or those that have heat-tolerant algae – can withstand the heat of bleaching events.

The Intergovernmental Panel on Climate Change report predicts that under 2 ° C of global warming, 99% of coral reefs will shrink. “As we move forward, we know the water is going to get warmer, not only much, much warmer, but also much faster,” Quigley said.

For the first time this year, the team hopes to selectively breed a species of Porites coral – slow-growing massive corals that look like boulders. If successful, this will be the sixth species included in the program.

Broodstock collection in far north Queensland
According to scientists, the number one priority to save the reef is to reduce carbon emissions. Photography: Marie Roman / AIMS

The Great Barrier Reef contains around 400 different species of coral, estimates Professor Terry Hughes, an internationally renowned coral reef scientist at James Cook University.

AIMS research sheds light on characteristics of wild corals following recent bleaching events, says Hughes. “This tells us about their heat tolerance, it tells us if this heat tolerance is changing.

“We’re also getting much-needed information about how the barrier reef is wired in terms of the movement of larvae from one place to another – gene flow. “

Hughes, who heads the ARC Center of Excellence for Coral Reef Studies, says one obstacle for coral restoration projects is the huge scale they have to work on to have an impact.

“If you wanted to improve the coral cover [on the Great Barrier Reef] … By 1%, you would need corals that are 250m wide, ”he says. This would involve raising fast-growing coral species for about five years to bring them to the size of a plate. “As a route to intervention, ladder will always be the biggest challenge. “

Bay stresses that reef restoration “is not a quick fix. Climate change is a very significant threat to coral reefs and we need strong action on climate change to give us the best chance of survival in the future, ”she said.

Quigley agrees. “When you think of the scale of the ecosystems that are affected, like the Amazon, like the Great Barrier Reef, these are huge and complex ecosystems that people have studied for a long time, but we are only scratching the surface in terms fundamentally understanding how they work.

The number one priority to saving the reef is reducing carbon emissions, says Quigley. Management practices, such as water quality regulation, crown-of-thorns starfish removal programs, and fisheries management, will also help alleviate pressure on the ecosystem.

“And then, third, we can look at these innovative restaurant concepts,” she says. “We can start to think… what kind of restoration can we develop now, while there is still time. “


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