The cause of a mystery disease that is killing off a rare coral on the southwest coast of Britain has been identified by marine biologists from the University of Plymouth.

Scientists from the university have established that colonies of the pink sea fan, which is on the international Red List of threatened species, have become infected with bacteria.

A species of bacteria known as Vibrio splendidus is killing the cold-water corals by producing enzymes that attack their tissue. Some scientists suspect that the disease may be linked to higher water temperatures which stress the corals and reduce their natural resistance, or help harmful bacteria to thrive.

Pollution might also be responsible, though experts behind the research emphasise that they do not yet know what is causing the infections.

The pink sea fan, Eunicella verrucosa,is among the most spectacular of the soft corals native to the waters around the British Isles.

Though most people associate coral reefs with warm tropical waters, there are also many species that thrive in cold water.

In 2002, scientists discovered an outbreak of disease among pink sea fan populations off the island of Lundy in the Bristol Channel, in one of Britain’s only marine protected areas.

Many colonies began to die, and other outbreaks of the mystery disease have since been recorded off Plymouth and in Lyme Bay, The cause has been traced by a Plymouth team headed by Jason Hall-Spencer, one of Britain’s leading coral experts.

Much of the key work has been done by James Pike, an undergraduate student studying marine biology and oceanography, as part of his final-year project.

Mr Pike used underwater surveys and laboratory studies to identify the Vibrio splendidus bacteria. The research is published in the journal Diseases of Acquatic Organisms.

Dr Hall-Spencer said: “Many people know about tropical coral reefs but are completely unaware that British waters contain a huge diversity of life, including these corals.

“Diseases increasingly affect tropical corals but this is the first record of disease affecting cold-water corals.

“Pink sea fans are fully protected under UK legislation and are listed as a threatened species on the international Red List, so it is vitally important to find out why these protected species are dying.”

He said that while it is unlikely to be possible to treat the disease directly, the findings should raise awareness of the need to protect domestic cold-water corals from damage.

“Lots of people are concerned about coral disease and bleaching in tropical waters, but no one has been looking at the corals on our own doorstep,” he said. “Yet disease is happening here too.”

Colin Munn, a microbiologist working with the team, believes that global warming or other human influences could be contributing to the coral disease. He said: “It appears that the normal balance of microbes populating the sea fan has been disturbed, allowing disease-producing organisms to take over.

“What triggers this is still unclear, but it could be due to extreme temperatures or pollution.”

Dr Hall-Spencer, however, pointed out that the pink sea fan is at the northern end of its natural range in British waters, and that it is accustomed to hotter temperatures. But, warmer waters could be benefiting the bacteria that cause the disease, he said.

Scientists at the Zoological Society of London are attempting to breed the pink sea fan coral in the laboratory, which could eventually offer a means of preserving it, Dr Hall-Spencer said.

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