A team of researchers from the Australian Institute of Marine Science believes that a trio of viruses are infecting algae in the Great Barrier Reef and leading to the process of coral bleaching by attacking their Symbiodinium cells, which are crucial for their health.
In order for corals to thrive, they must possess a healthy symbiotic relationship with photosynthetic algae called Symbiodinium, which are single-celled organisms that reside in coral tissue and the source of up to 90 percent of the reef's nutrients. However, this relationship breaks down under elevated temperatures, which can halt the photosynthesis process and lead to the potentially fatal process of bleaching.
The research team, led by marine biologist Karen Weynberg, revealed that on top of the stress of climate change, there are three distinct viruses attacking the Symbiodinium cells in the Great Barrier Reef, as evidenced in their observations of the photosynthetic algae living in a lab culture consisting of samples collected from along the reef.
"In the cultures that we have... there seems to be this ongoing, persistent viral infection," Weynberg said. "It seems like Symbiodinium is really under attack, quite heavily, from three different types of viruses."
Weynberg and her team imaged and sequenced the genome of the viruses, revealing that it is highly likely that they are hindering the algae's ability to photosynthesize and, in turn, stimulating the process of coral bleaching.
Interestingly, previous research has shown that Symbiodinium cultures that are exposed to stresses - such as higher temperatures or ultraviolet light - typically experience rises in "latent viruses," pointing to climate change as a factor that could be adding the to problem. For example, a previous study found that the Great Barrier Reef is infected with a herpes-like virus and suggested that the outbreak stemmed from its increased vulnerability due to detrimental environmental conditions.
"I initially set out to repeat those experiments," Weynberg said. "But what I actually found was that, regardless of exposing the Symbiodinium in culture to stressors, the culture already had this persistent, prevalent infection going on... The viruses were actively replicating."
"This was completely unexpected," she added. "I was seeing viruses in my stress-free controls."
The findings were presented at the 2016 Ocean Sciences Meeting in New Orleans, La.
