Searching for the secret to coral reef survival

Researchers in north Queensland are breeding heat tolerant coral, hoping it might be one of the solutions needed to prevent disaster when the next marine heatwave hits the Great Barrier Reef.

The reef is located off the northeast coast of Australia and it stretches over 2,300 kilometres and encompasses an area of approximately 344,400 square kilometres. That makes it as big as Italy. It is comprised of over 2,900 individual coral reefs and 900 islands.

The reef is not only a UNESCO World Heritage Site but also a critical habitat for a vast array of marine life, including numerous species of fish, coral, and other marine organisms.

But as relentless heatwaves swept through the azure waters in 2016 and 2017, researchers observed and meticulously collected coral specimens. This period would be etched into the annals of coral history as a cataclysmic event, a heatwave that would bring about unprecedented devastation to the delicate ecosystem.

“When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die,” says Professor Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University.

“Averaged across the whole Great Barrier Reef, we lost 30 percent of the corals in the nine-month period between March and November 2016.”

Little did they know that the very corals they were carefully documenting would bear witness to the stark reality of climate change, marking a turning point in the struggle to preserve one of the world’s natural wonders.

Australia had lost close to half of the corals in shallow-water habitats across the northern two-thirds of the Great Barrier Reef due to back-to-back bleaching events.

It was thought the Great Barrier Reef was doomed.

Yet, in a remarkable turn of events, the once-embattled coral is making a resilient comeback following the devastating losses. This resurgence wasn’t a result of good fortune; rather, it is a testament to the delicate balance between environmental conditions and the reef’s ability to adapt.

But the reef’s luck may be running out as hotter El Niño conditions return, driving warmer ocean temperatures and increasing the risk of bleaching. “We have to fear that we will have another big event with lots of mortality like in 2016 and 2017. In an El Nino, we have extended periods where we don’t have cloud cover, and therefore the bleaching tends to be more damaging in those years,” said University of Queensland senior lecturer Dr. Selina Ward.

World Wildlife Fund Australia head of oceans Richard Leck agrees: “The reality is for anyone who cares about the reef is that the best we  can do is cross our fingers and hope that it’s cloudy or there’s a storm. […] We’re playing Russian roulette with the reef now, and it is inevitable that we will have a significant bleaching event in years to come.”

What if it wasn’t left to chance, though? What if the future of this ecological system was instead in the hands of innovative solutions to bolster the Great Barrier Reef’s resilience.

In a special editorial feature in Science, researchers unveiled strategies to accelerate the natural evolution of heat-tolerant corals, employ next-generation aquaculture for mass coral reproduction, and engage in collaborative decision-making with First Nations groups to strategically place these corals onto the reef.

The thing about coral is that no two are alike. They exhibit varying degrees of heat tolerance, with some capable of enduring higher temperatures for extended periods, while others undergo bleaching at lower temperatures.

Global bleaching thresholds have increased by 0.5°C in the past decade, suggesting that reefs are becoming more tolerant, potentially due to the adaptation of surviving species.

 To combat the escalating marine heatwaves threatening the Great Barrier Reef, breeding heat-tolerant coral is a must. But in order to do that, scientists must delve into the intricacies of coral microbiomes. Understanding the nuanced differences in heat tolerance among various coral species is fundamental; researchers investigate which corals exhibit superior heat resistance and then seek to unravel the genetic mechanisms that underlie this resilience. By identifying specific genetic markers and studying individual corals in warmer waters, they can pinpoint those with a higher likelihood of passing on heat-tolerant traits to subsequent generations in both aquaculture facilities and natural field conditions.

The team also enhanced the coral’s resilience to temperature-induced bleaching by fortifying the heat tolerance of its microalgal symbionts. These minute algae cells inhabit the coral tissue, contributing to the overall health and adaptive capacity of the coral in the face of changing environmental conditions. And the ‘assisted evolution’ methods, tested in laboratories, show promise for mass production.

“This breakthrough provides a promising and novel tool to increase the heat tolerance of corals and is a great win for Australian science,” says Queensland University of Technology’s Adjunct Professor Claudia Vickers (former Director of CSIRO’s Synthetic Biology FSP).

Traditionally, coral restoration has been a slow and expensive process conducted by hand in small laboratory aquarium facilities. But researchers in Townsville have been working on making the methodology faster. By settling selected baby corals on small tabs in modular sheets and attaching them to protective structures in the ocean, the scientific teams can significantly increase survival rates.

“Performance in the lab is one thing, finding a suitable home for these new recruits is another,” says the Great Barrier Reef Program.

Trials outlined in the Science article show that carefully chosen reef locations demonstrate the feasibility of large-scale production using boats or robots, automating coral rearing. While currently applicable to around 50 coral species on the Great Barrier Reef, the goal is to expand these technologies further. Ensuring the success of heat-resistant baby corals requires robust ecological models and decision-making processes that consider economic, social, and environmental factors.

As conservation efforts evolve from protecting ecosystems to actively aiding adaptation, time becomes a critical factor. In the face of accelerating disruptions, the collaborative efforts of scientists, Traditional Owners, and the broader community are essential to secure a vibrant and resilient future for the Great Barrier Reef. The science is commendable, the problem is scale.

The clock is ticking, and the need for action – both on the reef, and globally to stop warming – is urgent.