Scientists in Saudi Arabia are studying how microorganisms might help corals adapt to warmer ocean temperatures.
Corals harbour a microbiome that consists of microorganisms like bacteria, viruses, fungi and archaea that help them function and thrive. The microbiome is not set in stone; as the short-lived bacteria can adapt more quickly than the long-lived corals, this may be the key to protecting the corals in the face of rising temperatures.
“Our challenge is to untangle and understand the symbiotic interactions between corals and other organisms,” said Associate Professor of Marine Science Christian Voolstra at the Red Sea Research Center in King Abdullah University of Science & Technology (KAUST).
In a study led by KAUST, the researchers designed an experiment in which they monitored coral-bacterial interactions over time and studied their responses to the changes in water temperature.
They did this at two reef pools off Ofu Island in the National Park of American Samoa, which were in close proximity to each other and hosted the coral species Acroporahyacinthus. The temperatures in the two pools were different: the temperature of one rarely exceeded 32 degrees Celsius while the other fluctuated between 25 and 34 degrees Celsius.
After transplanting some coral fragments from one pool to the other, the scientists monitored them and their associated bacteria in both their native and new environments.
After seventeen months, a short-term heat-stress experiment showed that the corals that had been transplanted to the warmer pool had changed their associated bacteria and were more heat resistant.
“Their microbiome was similar to the corals native to the warmer pool. This suggests that bacterial associations are flexible and can potentially help corals adapt to changing environments--an exciting outcome!” said Professor Voolstra.
Further analysis of the microbial communities showed that the higher-temperature microbiomes had a higher-carbohydrate metabolism and a more functional sugar-transport system.
The next step of the research involves proving that specific bacteria can directly contribute to the host's thermal tolerance. "We can do this by showing that the absence of a bacterium renders the coral host heat sensitive, whereas an association with the same bacterium makes coral more heat tolerant," said Professor Voolstra, adding that finding the right bacteria was like finding a needle in a haystack.