Australian researchers have found corals build "cloud umbrellas" to protect themselves from the scorching sun, and say coral loss through bleaching events could have wider ramifications for weather and agricultural production along the Queensland coast.
A team of scientists from Griffith University, Southern Cross University and the University of Southern Queensland analysed satellite data spanning 15 years to find corals produce and release aerosols into the atmosphere to create a barrier of cloud cover to help keep themselves cool.
Associate Professor Albert Gabric from Griffith University said the study looked at a 100 square kilometre area around Heron Island in the southern Great Barrier Reef.
"The corals can get stressed by strong levels of irradiance or indeed warming, warm temperatures and ocean temperatures," he said.
"And what we've seen is a correlation or a connection between the amount of aerosols above the reef and the amount of stress the corals are undergoing."
Associate Professor Gabric said coral polyps produced "quite large quantities" of miniscule compounds, which underwent chemical transformations when they reached the air to form small particles in the lower atmosphere.
"The importance of these particles is that water vapour can condense around them," he said.
"So they form what's known technically as condensation nuclei, and are therefore very important in the creation of clouds and the modification of cloud properties like the brightness of clouds, and even the lifetime of clouds."
"So if you have a lot of these aerosol particles being emitted it basically changes the physics of clouds over that area.
"Without saying that corals are consciously going through that, over evolutionary timescales where we're talking millions of years or hundreds of millions of years, it's certainly possible corals have evolved a protection mechanism."
Artificial cloud cover for corals
Associate Professor Gabric said it might be possible to mimic the phenomenon by spraying sea salt into the air above the reef to generate aerosols to create cloud cover for corals.
"But on a large scale this would be quite expensive, so we need further research on how best to maintain and encourage natural coralline aerosol emissions," he said.
The findings were published in the journal, AMBIO.
Further bleaching could weaken corals' ability to protect themselves
Associate Professor Gabric said scientists were doing further studies to find out what impact bleaching had on corals' ability to influence clouds.
He said his PhD student Rebecca Jackson was specifically analysing satellite data over parts of the reef that had been bleached, including a major bleaching event in 2016.
"Very interestingly what she's found is the aerosol levels increased before the bleaching event, presumably as the corals have been stressed, and then after the bleaching event there's actually an abrupt drop in aerosols," he said.
"We can understand that because post-bleaching, the corals have expelled their symbiotic zooxanthellae, and we know that zooxanthellae are a source of these compounds.
"The concern there is of course if bleaching continues due to warming of the oceans, the corals will lose this protective mechanism, and therefore bleach more in the future and be more susceptible to warming."
Possible link between coral and clouds
Associate Professor Gabric said a decline in coral health could have wider implications for Queensland's climate, and subsequently on agricultural production.
"If the distribution of clouds is intricately connected to the health of the coral reef, and as we know clouds produce rain, then the continuing demise of coral reefs and that impact on cloud cover could certainly influence agriculture along the Queensland coastline.
"In other words, a decrease in rainfall, which we already know agriculture in Australia is very sensitive to."ABC