Corals control their climate with clouds

A Southern Cross University (SCU) research team has discovered that coral reefs may be able to control the climate and protect themselves from coral bleaching by creating their own cloud cover.

But that process could be under threat from high nutrient levels and increasing temperatures, according to research leader Associate Professor Graham Jones.

Dr Jones and his PhD students have spent the last 14 years studying the reef and have found that corals contain a chemical which helps to form clouds when released into the atmosphere. The chemical, dimethylsulphide (DMS), transforms into an aerosol of tiny particles on which water vapour can condense, forming clouds.

The finding, which was reported in the New Scientist (February 5), explains a phenomenon observed hundreds of years ago.

“We have had plenty of anecdotal evidence that clouds form over coral reefs. When you sail up to coral atolls or large coral reefs you can often see cloud banks forming over them. Early Pacific Islanders navigated back to their reefs after fishing expeditions by looking for those cloud formations over the reefs,” Dr Jones said.

“We believe this is a natural process that the coral reefs may use to regulate the amount of sunlight they receive, and keep water temperatures slightly cooler than if there were no clouds present. Whilst we know that phytoplankton play a vital part in regulating Earth’s climate, no one had looked at whether coral reefs might have a similar role.

“What we want to see now is what’s happening when the corals are stressed by increasing temperatures and high nutrient levels. The cloud cover is absolutely vital for the corals survival and the process which produces that may be breaking down.”

Dr Jones said research conducted by PhD student Esther Fischer in the laboratory indicated that when there were high nutrient levels, the corals did not produce as much DMS.

For the in-shore coral reefs in the Great Barrier Reef that could provide clues to the mass coral bleaching episodes that occurred in 1998 and 2002, when over 600 reefs bleached due to high seawater temperatures.

“The reef is not getting the protection it had 20 or 30 years ago and we need to find out the reason for that. It could be a combination of two effects – high temperatures caused by greenhouse gases and high levels of nutrients from the land.”

Dr Jones will be working with the Australian Institute of Marine Science near Townsville later this year to conduct further testing on the release of DMS from corals and to examine the links between coral reefs and the local climate.

“We need to gather a multi-disciplinary team to look at these natural aerosol substances in the atmosphere over the Great Barrier Reef and how they affect sunlight.”

Photo caption: Bleached corals in the Great Barrier Reef showing loss of colour and unable to produce DMS. Photo: Ray Berkelmans, AIMS.