UC Santa Cruz researchers say densovirus may be responsible for wiping out West Coast starfish

Posted with permission from SEAFOODNEWS.COM

[San Francisco Chronicle] by Peter Fimrite – November 18, 2014

Scientists have identified a virus that they believe is the mysterious killer that is wiping out starfish along the Pacific coast, but they can’t figure out why it suddenly became so deadly or whether it will continue its reign of destruction.

The pathogen believed responsible for causing millions of sea stars along the coast of California to wither and die was identified as a densovirus, a type of parvovirus, researchers at UC Santa Cruz and Cornell University said Monday.The disease was found not only in the tissues of its victims, but in brittle stars, which are closely related, and sea urchins.

It was also in seawater and sediments collected from affected areas, including Santa Cruz and Monterey, according to a paper published Monday in the Proceedings of the National Academy of Sciences.  Strangely, the virus was also detected in museum specimens dating back to 1942, meaning the disease has been lurking for decades but only recently turned deadly, said co-author Peter Raimondi, chairman of the ecology and evolutionary biology department at UC Santa Cruz. The virus wiped out starfish along huge swaths of the coast from Mexico to Alaska starting last year and has recently gone on a rampage through the Olympic Coast, in Washington state.

“What is unresolved is why it is so virulent,” said Raimondi, who leads the Pacific Rocky Intertidal Monitoring Program, which has been documenting the spread of the disease along the West Coast. “This virus has been around for at least 70 years, which brings up the question of why now?”

Another conundrum, said Raimondi, is the fact that the virus is present in other species, like sea urchins, which have not been dying nearly as much as starfish.

“Even if they don’t get infected, they carry it,” Raimondi said of the sea urchins. “That could be very problematic with respect to recovery.”

The mysterious pathogen, dubbed sea star wasting disease, was first detected in the summer of 2013 in Southern California. It was then found in tide pool areas along the coast of Monterey and has since spread through Oregon, Washington, British Columbia and southern Alaska. The telltale sign of the syndrome was that it caused starfish to become mushy and deteriorate until body parts began falling off.  Dead and dying starfish have been found close to shore and deeper underwater.

The disease even found its way last year into the filtration system of the Monterey Bay Aquarium, which uses seawater in its tanks. The virus has ravaged 20 varieties of starfish, going through a kind of progression, usually starting with the Ochre star, the purple or orange starfish most commonly seen in intertidal regions, Raimondi said. The pathogen has also ravaged the population of sunflower stars, the largest sea stars in the world. Short-spined sea stars and giant sea stars have also been hit hard. Raimondi said starfish feed on a variety of invertebrates, including mussels, sea urchins, clams and snails, which could be a source of the spreading disease.

The pathogen can also spread in the water almost like the common cold among the dense, often interwoven, populations of starfish, he said.The disappearance of starfish could have serious consequences by shifting the ecological balance of the sea. Mussels and other starfish prey could begin to overpopulate areas where their numbers were once controlled, Raimondi said. As a result, he said, fish, invertebrates, crabs and other species that feed on algae, plants and other sea life that thrive when starfish are in control will be marginalized and forced to look elsewhere for food.

Signs of hope

There is a light, however, amid the darkness. Huge numbers of baby sea stars have appeared in previously devastated sites in the Monterey Bay region, according to surveys conducted this year. In one study site, on a reef called Terrace Point, off Santa Cruz, researchers found more juvenile sea stars than have seen in 15 years of monitoring.

“There were just immense numbers of babies,” said Raimondi, who believes the diseased and dying sea stars went into reproductive mode, shooting out sperm and eggs as an evolutionary response to stress. “If they live, it’s going to mean we are going to have a recovery here in the next few years.”

Problem persists

Raimondi said the discovery of the suspected killer does not resolve the problem, but it helps in the quest to figure out what is going on in the ocean and, perhaps, prepare for change.

“One question is whether this virus evolved and became much more lethal,” Raimondi said. “The other possibility is that there is an environmental stress that is causing sea stars to become more susceptible, for instance warmer water or ocean acidification. It could be both. We don’t know. Our research will be looking at whether this is an isolated example or whether these things could become more common in the future. One question is whether this virus evolved and became much more lethal.”

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