Last December, marine biologist Caitlin Lawson made her way to the Great Barrier Reef.

Like countless others, she was there for the annual spawning of the corals. However, she was armed, not with expensive photographic equipment, but small plastic containers rigged with tubing.

Her mission? To collect the gaseous chemicals released by the corals (as well as their algal and bacterial symbionts) before, during and after the spawning event.

Volatile gasses

All organisms release volatile gases and the mix of these gasses emitted is an indication of the organisms’ health and can even influence how it copes with stress.

This process has been much studied in the case in terrestrial organisms, but not so in underwater organisms.

Until now.

Analytical chemistry

After collecting the samples at the Great Barrier Reef, Dr. Lawson (from the UTS Climate Change Cluster) and her team used advanced analytical chemistry techniques to characterise and measure the volatile chemicals released by the corals.

The findings of this study, which was published in the Global Change Biology journal, focused on two common reef-building corals—Acropora intermedia and Pocillopora damicornis—and the effect heat stress (read climate change) had on their gaseous emissions.

“Our results provide the first insights into the range of gases produced by reef-building corals and highlight a diverse suite of compounds that may play potentially important—but previously unrecognised—roles in maintaining healthy reef functioning,” said Dr Lawson.

Heat stress

During heat stress experiments in which the water temperature was increased by five percent, the abundance and chemical diversity of the corals' gas emissions fell significantly; this occurred across all the coral species in the study, illustrating the corals’ compromised ability to cope with increasing temperatures.

In addition, a total of 87 volatile chemicals were detected from the two species. Surprised at the large amount, coauthor Dr Jean-Baptiste Raine said in a press release that the number was “just going to keep growing, the more we look into it and the more species we start to investigate."

Most of the chemicals identified were associated with climate regulation, so it was possible that a change in the chemical composition would affect climatic factors like the local cloud cover.

Coral stress

In terms of modelling climactic processes, Lawson speculates that the chemicals being released into the atmosphere by the corals may be a significant source that have been overlooked.

And because the presence of volatile chemicals has been known to be an indicator of illness in some animals, it is possible that the mix of chemicals released by corals may be used as a measure of coral stress and disease.

Coral communication

Lawson was also keen to explore the chemicals as a means of communication: “I get really excited about the signalling that could be happening between different species of corals, or whether they have certain smells that they'll release that might attract grazing fish if there's too much algae. Is there a certain smell that indicates corals are more vulnerable?”

“With the increasing frequency of heat stress events—and it is looking likely that bleaching will occur again in early 2021—it is even more important that we understand coral emissions as they may prove to be a key tool in our efforts to monitor and conserve coral reefs,” she added.