A light misting for the Great Barrier Reef

Two scientists with a massive misting cannon and a drone walk on to a sports field. No, it’s not the starting line of a joke, but the early phase of a new trial exploring a novel approach to preventing coral bleaching on Australia’s precious but beleaguered Great Barrier Reef (GBR).

The research, run by scientists from the Queensland University of Technology (QUT) and Southern Cross University, is part of the Reef Restoration and Adaptation Program (RRAP), a partnership between the Australian Government and the Great Barrier Reef Foundation to prepare the natural wonder for the ravaging impacts of climate change.

The GBR has experienced massive bleaching events in its recent history, including in the summer of 2019-20, when 60% of the corals surveyed by scientists were shown to have suffered either moderate or severe bleaching. 

According to RRAP director Cedric Robillot, the reef’s single biggest threat is climate change, though the reef, which is actually a nexus of connected reefs covering an area larger than the UK, Switzerland and Holland combined, isn’t on its deathbed just yet – mild or moderately bleached corals can make a comeback

According to Joel Alroe, an atmospheric scientist at QUT, the experiment at the University’s sports field was a test run of the team’s prototype sprayer system, designed to spray a fine mist of seawater across large areas of the reef, with the goal of shading and cooling the water to prevent bleaching during stressful weather conditions.

The team rolled the mister out onto the playing field and turned it on, then measured how much incoming sunlight the mist prevented from shining on the field’s surface.

Reef mist experiment 25112021 2058 min
Zoran Ristovski and Joel Alroe, atmospheric scientists at QUT, in front of the misting cannon they hope to use to help mitigate coral bleaching on the Great Barrier Reef. Credit: QUT

“We measured changes in the ground-level solar radiation and sampled the plume from an eight-metre mast installed mid-field to understand the microphysics of the mist plume and the plume’s dispersal,” Alroe says.

“The team’s initial results showed that, under the right conditions, a single sprayer could generate a short-lived plume capable of blanketing a sports field and producing a measurable reduction in the incoming sunlight.”

But how does an on-land test translate to the reef? 

“Our aim is to reduce the sun’s intensity over the reef by generating a low-lying mist directly over the ocean surface during extended periods of still and hot weather (known as the doldrums) when the coral is most at risk of stress and bleaching.

“We know that these conditions are one of the factors causing reef damage and that clouds and fog effectively reflect a proportion of the sunlight, reducing the impact on the underlying reef.”

The next step, according to QUT atmospheric scientist Zoran Ristovski, is to take the mister out on the high seas and see how it works – the first ship trials have already been conducted.

“If this method is successful, the sprayer system would then be scaled up to produce larger plumes capable of shading vulnerable reefs.

“This misting idea is intended as a short-term protection for areas of the reef. When the water temperature is high, the corals become stressed and vulnerable to intense sunlight and UV rays, leading to bleaching. So, the misting could be needed for several days at a time to shade the surface and reflect the UV until the weather conditions become more hospitable.”

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