For reef-building corals, not just any symbiotic algae will do, new research shows.
The findings are important because they amount to another danger sign for the world’s coral reefs, which rely on a partnership with the millions of phototrophic algae they host to obtain food.
Global climate change is threatening the reefs in part because the symbionts, dinoflagellates of the genus Symbiodinium, can be stressed by warming oceans to the point of dysbiosis – a collapse of the host-symbiont partnership, which results in a phenomenon known as coral bleaching.
Earlier studies had suggested the more heat-tolerant Symbiodinium trenchii might be able to take the place of other, more sensitive species of Symbiodinium.
But an international research group that included Virginia Weis, Eli Meyer and Camerron Crowder of Oregon State University found that likely won’t be the case.
“Our research suggests that while S. trenchii might be able to establish a population in a host, it’s not correct to say it will be a beneficial partnership for the coral,” said Weis, professor of integrative biology in OSU’s College of Science.
Findings were published today in the Proceedings of the National Academy of Sciences.
Weis and collaborators at Victoria University of Wellington in New Zealand, the University of Melbourne and Stanford University worked with the sea anemone Exaiptasia pallida, commonly called Aiptasia, an established model for studying the type of symbiosis upon which coral reefs rely.
“Corals are really hard to grow in a lab,” Weis said. “They’re very fussy, they’re slow growing, and many of them are endangered. But this anemone grows very fast and is easy to manipulate.”
Aiptasia anemones were colonized separately with S. trenchii and their native symbionts, S. minutum.S. trenchii has been observed to invade corals after bleaching – when the corals become stressed and lose their algae.
“When we challenged Aiptasia with the regular symbiont, it went as expected,” Weis said. “There was no immune system response, and there was productivity – we could see signs of the host getting sugars and nutrients from its symbiont.”
But with the introduction of S. trenchii, it was a much different story.
“We got a completely different set of signals,” she said….