Scientists have selectively shaded bleached corals on the Great Barrier Reef – gaining critical in-field data to inform future large-scale interventions that could help coral reefs become more resilient in the face of climate change.
Last summer, following localised bleaching near Lizard Island, a science team from the Australian Institute of Marine Science (AIMS) installed three levels of underwater shade structures over areas of bleaching coral colonies experiencing heat stress.
The team returned to Lizard Island Research Station, in the far northern Great Barrier Reef, in spring to survey the sites to see how recovery of bleached colonies compared between the shaded and unshaded reef communities.
The experiment is set to determine if reducing light intensity can help corals survive severe heatwaves as well as answer other important reef restoration questions.
AIMS coral ecophysiologist and project leader Dr Neal Cantin said apart from water temperature, there were three main drivers that raised the risk of coral mortality during a heatwave: intense sunlight, water clarity and the speed of water flow through the reef.
“If we can eliminate one of these main drivers of bleaching, such as intense sunlight during peak heat wave conditions, we might be able to ease the corals’ stress level enough to help reduce mortality,” he said.
“This shading experiment will provide critical information to tell us the best way we can intervene and help corals survive future bleaching events.
“It’s allowing us to see in real-time, under real-world reef conditions, how corals respond to these high stress periods.”
The intention of the experiment is not to trial shade structures as an intervention, but rather to inform the bigger engineering approaches to reduce light on a larger scale, such as cloud brightening or fogging.
The cloud brightening intervention, led by Southern Cross University’s Dr Dan Harrison, involves spraying trillions of nano-sized ocean salt crystals into the air to reflect sunlight away from the ocean surface and cool coral reefs.
“Cloud brightening is one of the most promising interventions that could potentially be applied to the entire Great Barrier Reef during a coral bleaching event,” Dr Harrison said.
“This AIMS shading experiment is filling key knowledge gaps and providing essential data to ensure the successful development and implementation of cloud brightening.”
AIMS Research Program Director Dr Britta Schaffelke said marine heatwaves were predicted to become more intense and more frequent due to climate change.
“This means higher temperatures will last longer across greater areas of the Reef, leading to more bleaching more often,” she said.
“If we can engineer approaches that can reduce the intensity of sunlight over reefs during the peak summer periods that drive bleaching, we might be able to reduce the bleaching related mortality.
“While reducing emissions is the most critical long-term solution to protect coral reefs, restoration and adaptation initiatives can play a significant role in protecting the reefs from the escalating effects of climate change.”
The AIMS project is part of the Australian Government’s Reef Restoration and Adaptation Program with the Great Barrier Reef Foundation – a program fast-tracking interventions to help reefs resist, adapt and recover from the effects of climate change.