By Craig Welch
It’s not clear if a virus wiping out millions of sea stars is being influenced by climate change. But scientists say rising temperatures likely will make ocean disease outbreaks more problematic in the future.
The shellfish pathogen that hit California’s Channel Islands in the 1980s began to quickly kill one of the tideland’s most important animals — black abalone.
But what unnerved scientists was what they learned next: Whenever ocean waters grew warmer, the deadly infection known as withering syndrome spread and killed even more abalone.
By the 2000s, this phenomenon had helped transform black abalone into an endangered species — and a symbol of how much climate change may one day influence the spread of marine diseases.
Long before a virus would kill West Coast sea stars by the millions, scientists had begun to wonder when a major human-caused marine-disease outbreak would strike. Now they’re wondering if so-called sea-star wasting disease is an example of the threat they predicted — or just part of a natural cycle they don’t yet understand.
This month, scientists announced they’d identified the culprit responsible for a mass die-off of 20 species of starfish that started in Washington last year, and then spread to Southern California and north to Alaska. The cause was a virus that had been found in sea stars since at least the 1940s. But it had never killed anywhere near as many creatures or across so vast an area.
It’s too soon to say whether the sudden explosion of this starfish disease is linked to environmental changes wrought by humans, such as global warming or ocean acidification, which is the souring of seas by carbon-dioxide emissions.
But scientists say the die-off may be the most extensive marine-disease event ever documented. Few experts believe it will be the last.
“The most dire interpretation of the sea-star event is that it could just be the first in a wave of similar events,” said Bruce Menge, a marine-biology professor at Oregon State University.
In fact, from work with corals and eelgrass, dolphins, seals and fish, researchers increasingly are finding that climate change is likely to affect disease susceptibility and transmission in a host of important ways.
“A warmer world is a sicker world,” said C. Drew Harvell, a marine epidemiologist and coral-disease expert from Cornell University who has played a key role in studying the sea-star die-off. “A warming world can cause disease to increase, both by compromising the host and because a lot of microorganisms become more virulent or are happier at warmer temperatures.”
A parasite that affects East Coast oysters offers one of the clearest examples of how a warming world may change ocean diseases.
The pathogen can kill masses of oysters but was rarely seen north of the Chesapeake Bay. Then, in the late 1980s and early 1990s, a warm-water system allowed the parasite to quickly spread from Maryland to Cape Cod, Mass., and beyond. There, it infected more oysters faster than before and killed them far quicker.
Many pathogens tend to get knocked back by cold winters. But as the marine world continues to warm, their survivability and suitable habitat just expands.
“In my opinion, we’re going to see more infectious-disease outbreaks in the ocean,” said Colleen Burge, a research associate at the University of Washington and lead author of a major study of ocean pathogens published last year. More....