Herpes has devastated 26 percent of France's oyster production since the summer of 2008. Halfway around the world in Australia, the virus killed 10 million oysters in three days.
Researchers suspect climate change risks compounding the losses.
To learn more about how the virus and warmer ocean water affects Pacific oysters, researchers at CSIRO, Australia's national science agency, and the University of Tasmania are using dental gum to attach heart-rate monitors to a half-dozen of them. Another dozen Pacific oysters are wired up in an indoor lab, where light and temperature are modified to gauge changes in the oysters' physiological reactions.
"You can stand at a fence and look at your cow or your sheep, but you can't do that with an oyster," said Nick Elliott, research group leader at the Commonwealth Scientific and Industrial Research Organisation's agriculture flagship, which is leading the research team in Hobart, Tasmania. "Their faces don't tell you how they're performing."
Elliott hopes the oysters' reaction will answer questions plaguing a 3.3 billion-euro global industry grappling with a herpes virus that can have a 100 percent mortality rate. Results may also shed light on how to mitigate the effects of a warming ocean on a global fisheries and aquaculture industry that provides as much as 16.5 per cent of the protein eaten by the world's population, according to the World Health Organization.
Ostreid herpesvirus-1, also known as Pacific Oyster Mortality Syndrome, can kill most of a farm's stock of young shellfish in a day and has been linked to oyster deaths in Europe, Australia and New Zealand. It mostly strikes oysters that are under a year old, according to French research group Institut Francais de Recherche pour l'Exploitation de la Mer.
In Europe, the virus starts killing oysters when water temperatures reach about 16 degrees Celsius.
Combined land and ocean surface temperatures have warmed 0.85 of a degree Celsius since 1880, according to the Intergovernmental Panel on Climate Change. Continued emissions of greenhouse gases will cause further warming and changes in all parts of the climate system, it said in a 2014 report.
Temperatures this year are on course for their highest globally since records began, with oceans bearing the brunt of the heat and the United States and Canada spared the worst, says the World Meteorological Organization.
The ocean absorbs about a quarter of the carbon dioxide released each year from human activities, increasing its acidity and making it harder for animals to form shells. Oysters are susceptible to changes in water chemistry, temperature and the availability of food, such as algae or plankton, because they are filter feeders, according to the National Climate Change Adaptation Research Facility in Southport, Australia.
"When you're farming oysters, you're not actively feeding them," said John McCulloch, a research engineer in the digital productivity flagship at the CSIRO. "It really relies on the natural mix of algae as a food source, and that will vary quite significantly with even small changes in climate."
A warmer climate is already being felt 17,000 kilometres away from Tasmania in Maine, where the state's mudflats have become acidic enough in some spots to kill young clams. Rising acidity robs seawater of carbonate ions, an essential ingredient used by animals like shellfish and corals to build their shells, according to the New York-based National Resources Defense Council.
Oyster herpes doesn't harm people and is unrelated to the virus that infects humans. You won't catch it by eating affected oysters. Not that you would want to get anywhere near it. Sea creatures eat the meat from dead oysters and any left after the shellfish comes out of water smells rotten.
Oyster lovers in France are already paying more to satisfy their yen. Wholesale prices for French oysters have surged 36 percent since December 2008, data from the National Institute of Statistics and Economic Studies in Paris show.
The herpes virus slashed France's Pacific cupped oyster harvest to 82,000 metric tonness in 2012 from 103,799 tons in 2008, when the virus first appeared, and 110,800 tonness in 2007, according to the Food and Agriculture Organization of the United Nations.
The sensors on the Tasmanian oysters may pick up changes in the animal if it is able to detect the virus or if there is a trigger that could indicate to a farmer to take the oysters out of the water so they don't get herpes, said CSIRO's Elliott.
While herpes infections have occurred before in the U.S., Japan and Europe, "in 2008 in the summer in France, something changed," said Richard Whittington, professor of animal health at the University of Sydney. "It appears there was a mutation in one of those historically common viruses to turn it from being an occasional nuisance to a killer. And it was a killer in unprecedented proportions."
The virus was identified in New Zealand in 2010 and can be found in three estuaries in Australia's New South Wales state. It has also been detected in wild Pacific oysters in the state's Brisbane Water estuary. In the Hawkesbury River in New South Wales, the virus killed 10 million oysters within three days, according to University of Sydney's Whittington.
Pacific oysters are only a small part of the New South Wales industry, whereas South Australia and Tasmania produce the Pacific variety almost exclusively, according to Graham Mair, program manager of production innovation at the Adelaide-based Australian Seafood Cooperative Research Centre.
Australia's oyster industry is worth about A100 million dollars (67 million euros) each year, according to the government.
While no one knows how herpes travelled to Australia or New Zealand, it may spread via its food.
The virus could attach itself to plankton particles, according to the University of Sydney's Whittington. Researchers from the university have been able to filter water, separating the plankton that has the virus attached, and safely rear baby oysters, called spats. The project has also shown that raising oysters by 30 centimetres, giving them more time out of the water each tide cycle, helps older oysters. Animals in the middle of that range aren't really helped by either and are still susceptible to herpes, he said.
In New Zealand, where production tumbled by as much as 60 per cent, scientists are trying to breed animals that are resilient to the virus.
The Australian Competition and Consumer Commission this month approved a levy on the purchase of spat for as much as 10 years to allow research into developing herpes-resistant animals.
"If the virus moves to Tasmania and South Australia, then our national oyster industry is in very big trouble," said Mair, of the Seafood Cooperative Research Centre.
Phoebe Sedgman – Bloomberg News
— With assistance from Rudy Ruitenberg in Paris.