Coral communicates with the algae that give many reefs their colour — which could explain why reefs around the world are dying, scientists say.

Genetic analysis shows that coral has surprisingly complex genomes, sharing some of the same genes as human beings, which help it to maintain a delicate symbiotic relationship with the algae living within its body. These algae are crucial to the coral’s survival and also give reefs their vibrant hues.

The disruption of these “conversations” with algae could be behind the collapse of coral ecosystems around the world, researchers believe.

The warming of the world’s oceans, coupled with the acidification of sea water, is putting coral under great stress. Reefs around the world are being bleached as the loss of algae drains the coral of colour until, eventually, it dies.

It is estimated that more than 20 per cent of reefs are already dead, leaving the rich eco-systems that surround them on the verge of collapse.

Virginia Weis, of Oregon State University, a co-author of a discussion paper in the journal Science, said scientists had guessed that corals and algae must communicate, but until now had been unable to show how. “What has changed all of this is genomics,” she told The Times, adding that genes important in the communication between microbes and humans were also present in corals.

Corals are tiny individual polyps that secrete calcium carbonate to form external skeletons. Over time, these build into the huge reefs found in tropical waters around the world. Within the bodies of the coral live algae, which use photosynthesis to produce sugars vital to the coral’s survival.

Professor Weis said: “Some of these algae that live within corals are amazingly productive, and in some cases give 95 per cent of the sugars they produce to the coral to use for energy. In return the algae gained the nitrogen they neededby feeding off the waste from the coral.

“It’s a finely developed symbiotic relationship. The algae use a variety of molecules to signal to the coral that all is well and that it is not an intruder,” she said.

“Even though the coral depends on the algae for much of its food, it may be largely unaware of its presence. We now believe that what is happening when the water warms — or something else stresses the coral — is that the communication from the algae to the coral breaks down, the ‘all is well’ message doesn’t get through, then the algae essentially come out of hiding and face an immune response from the coral.”

Professor Weis said that the knowledge would not on its own prevent bleaching, “but understanding this communication — and how it varies with the myriad different coral-algae combinations across the globe — might help us to predict how corals will respond to rapid warming and help us to predict their ability to adapt and tolerate the change”.

In their discussion of the latest research in Science, Professor Weis and Denis Allemand, of the University of Nice Sophia Antipolis, in the South of France, also say that the calcification process that creates reefs is governed by the same gene that controls skeletal development in humans.

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