I’ll never forget my visit this past summer to the Lofall dock and nearby beach on Hood Canal in North Kitsap. It was a scene of devastation, in which starfish of all sizes were losing their limbs and decomposing into gooey masses.
My guides on the excursion were three women who had been watching for changes in sea stars as part of a volunteer monitoring program being conducted up and down the West Coast. The three were shocked at what they saw on the trip, as I described in a story for the Kitsap Sun as well as in a blog post in Water Ways.
Now, researchers are reporting that a virus, known as densovirus, appears to be playing a central role in the devastation of millions of sea stars from Alaska to Mexico. Their findings were reported in the Proceedings of the National Academy of Sciences (PDF 1.1 mb).
Many questions remain about the mysterious affliction known as “sea star wasting syndrome.” For one, why were the sea stars affected over such a wide area, all at about the same time?
As described in the report, the researchers went to museums with sea stars preserved in alcohol and found that the virus was present in specimens collected as long ago as 1942 at various West Coast sites. Minor outbreaks of the wasting syndrome have been reported through the years, but obviously something much bigger is taking place now.
A change in the environment, such as ocean acidification, has been suggested as one possibility. A change in the virus, such as we see for the flu virus in humans, is another idea. It could also be related to an over-population among the sea stars themselves.
Jeff Adams of Washington Sea Grant, who is leading the local monitoring program in Kitsap County, said it is good that researchers have found something to go on, but other causative factors are yet to be discovered.
“Why and where; those are two of the things still on the table,” Jeff told me. “What are the environmental factors that drove this much larger die-off? Was it something that made the virus more prevalent or something that made the sea stars weaker?”
Jeff noted that the cause of death may not be the virus itself but rather opportunistic pathogens that attack the sea stars after their immune systems are weakened by the virus.
“Density may have played a factor,” he said. “Sea star populations have been thick and strong over the past 12 years. When you get a lot of individuals in close proximity, you can get sudden changes. Marine populations fluctuate quite a bit naturally.”
Jeff hopes to maintain the volunteer monitoring program for years to come, not just to track the disease but to understand more about the cycles of marine life. Of course, he would like to be able to report on an ongoing recovery of sea star populations from their current state of devastation. Will the recovery occur in patches or uniformly at all monitored sites?
“Ideally, this will run its course, and we will start seeing juveniles showing up over the course of the summer,” he said. “How many of them will disappear?
“Ideally, we will be able to maintain some sites for much longer. For me, as a naturalist, there are lots of questions about natural historical cycles that have not been addressed. A lot of critters are facing challenges (to their survival).”
In Puget Sound, these challenges range from loss of habitat to pollution to climate change, and the predator-prey balance will determine whether any population —and ultimately entire species — can survive.
Linda Martin, one of the volunteers who gave me a tour of the Lofall beach, said she was glad that researchers have identified a viral cause of the sea-star devastation, but it remains unclear how that is going to help the population recover.
Because of the timing of low tide, the three women have not been to Lofall since early October, when the population was “completely depleted,” according to Linda. But they are planning to go back next weekend.
“We are anxious to go out and see if there is anything there,” she said. “We have not seen any juveniles for a long time. Originally, when we started out, we were seeing uncountable numbers of juveniles.”
As for the new findings, I thought it was interesting how the researchers removed tissues from diseased sea stars then filtered out everything down to the size of viruses. After that, they exposed one group of healthy sea stars to a raw sample of the fluid and another group to a heat-treated sample. The raw sample caused disease, but the heat-treated sample did not.
They then used DNA techniques to identify the virus, which was found in larger and larger concentrations as the disease progressed. Check out the research report in the Proceedings of the NAS (PDF 1.1 mb).
Jeff Barnard of the Associated Press interviewed researchers involved in the study and others familiar with the problem.