Communication between corals and algae may be impaired by climate change

The intricate symbiotic relationship between reef building corals and algae seem to rely on a delicate communication process between the algae and the coral, where the algae is constantly telling the coral that the algae belongs inside it, and that everything is fine. Without this communication, the algae would be treated as any other invader, e.g. a parasite, and be expelled by the coral’s immune system.

Researchers now fear that increased water temperature will impair this communication system, something which might prove to be the final blow for corals already threatened by pollution, acidification, overfishing, dynamite fishing, and sedimentation caused by deforestation.

According to a new report, a lack of communication is likely to be the underlying cause of coral bleaching and the collapse of coral reef ecosystems around the world.

Reef building corals can defend themselves and kill plankton for food, but despite this they can not survive without the tiny algae living inside them. Algae, which are a type of plants, can do what corals can’t – use sunlight to produce sugars and fix carbon through photosynthesis.

“Some of these algae that live within corals are amazingly productive, and in some cases give 95 percent of the sugars they produce to the coral to use for energy,” said Virginia Weis, a professor of zoology at Oregon State University. “In return the algae gain nitrogen, a limiting nutrient in the ocean, by feeding off the waste from the coral. It’s a finely developed symbiotic relationship.

If this relationship were to collapse, it would be death sentence for the reef building corals.

Even though the coral depends on the algae for much of its food, it may be largely unaware of its presence, said Weis. We now believe that this is what’s happening when the water warms or something else stresses the coral – the communication from the algae to the coral breaks down, the all-is-well message doesn’t get through, the algae essentially comes out of hiding and faces an immune response from the coral.”

This internal communication process, Weis said, is not unlike some of the biological processes found in humans and other animals.

Researchers now hope that some of the numerous species of reef building corals found globally and their algae will be more apt at handling change.

“With some of the new findings about coral symbiosis and calcification, and how it works, coral biologists are now starting to think more outside the box,” Weis said. “Maybe there’s something we could do to help identify and protect coral species that can survive in different conditions. Perhaps we won’t have to just stand by as the coral reefs of the world die and disappear.”

The new research has been published in the most recent issue of the journal Science and was funded in part by the U.S. National Science Foundation.