Researchers at the University of Southern California have made a discovery that may bring hope for the world’s corals.
Thus far, things have looked pretty grim for corals. About half of the world’s corals have been lost due to warming seas that make their world hostile. This is what’s responsible for “coral bleaching,” in which the normally vivid and floral creatures become pale and dead. This phenomenon happens because algae live symbiotically with corals, and when the corals are stressed they expel their algae.
But in aquariums at USC and at the Australian Institute of Marine Science, the researchers have found that some corals can “shuffle” the algae that are their symbionts in order to potentially gain an evolutionary advantage in a changing environment. Adult corals with this ability can also pass it along to their offspring.
This phenomenon had never been seen before, until scientists began captive breeding research in labs in the U.S. and Australia.
“What we’re finding is that corals can pass their shuffled complement of algal partners, or symbionts, to their offspring to bestow a potential survival advantage, and that’s a new discovery,” said USC Assistant Professor of Biology Carly Kenkel. “We care about this because coral reefs do so much for us. A reef provides a breakwater for storms, fish protein people need, and biodiversity we love and find beautiful.”
Scientists have known for a long time that coral and algae have a symbiotic relationship. The two creatures live as one: the coral is a soft-bodied polyp animal similar to a sea anemone or jellyfish, and algae live within the cells of the coral polyp. The corals provide the algae with safety from predators and substances for photosynthesis, and the algae produce oxygen, help remove wastes, and supply the coral with energy. The corals use this energy to make calcium carbonate, the rigid architecture that builds reefs, and the algae contribute to the corals’ beautiful colors. But when environmental stresses occur, the partnership is disrupted.
In their research, the scientists focused on two consecutive coral spawning seasons—one under normal conditions during 2015, and one during the global mass coral bleaching event of 2016. Using DNA sequencing, they screened which corals showed the ability to shuffle their symbionts and if the change was reflected in their offspring. They found that the number and type of algae cells differed considerably from 2015 to 2016, as measured by cell densities and photosynthesis output.
“To our knowledge, this is the first evidence that shuffled [symbiont] communities…can be inherited by offspring and supports the hypothesis that shuffling in microbial communities may serve as a mechanism of rapid coral acclimation to changing environmental conditions,” the study’s authors wrote.
So, corals may be more adaptable to the changing climate than previously thought—but is it enough?
Corals face a huge challenge as ocean warming increases: according to a UN report, the world’s coral reefs are the epicenter for climate change impacts and species loss. If the world warms another 0.9 degrees Fahrenheit, which is increasingly likely given the current U.S. administration’s lack of concern and lack of belief in global warming, coral reefs could dwindle by 70 to 90 percent. If the global temperature rises 1.8 degrees, 99 percent of the world’s corals will be in trouble.
“Corals have more mechanisms than we thought to deal with climate change, but they’re fighting with a tiny sword against a foe that’s like a tank,” Kenkel said. “Their adaptability may not be enough. They need time so they can adapt.”