Sea stars under attack

What is killing our sea stars?

If a mysterious disease keeps spreading, we may no longer see sea stars along the seashore

A year ago sea stars, commonly known as starfish, started disintegrating on the shores of Howe Sound, hit by a mysterious condition referred to as sea star wasting syndrome. The syndrome has decimated sea star colonies from British Columbia to California. UBC marine biologist Chris Harley discusses the effects of this puzzling condition, and what might be causing it.

What is sea star wasting disease, and what is causing it?

The symptoms are dreadful. First, the sea stars get swollen and lose their arms, then eventually die and start to decompose in place. You find pieces of sea star arms that have fallen off and crawled a little ways away—they’ll go about a metre or so before they run out of gas. Once they start showing symptoms, they die within a day or two.

As for what’s causing it, we’re not sure. Sea stars are known to be vulnerable to big disease outbreaks, but nobody’s seen anything of this magnitude before on our coast. Several research groups are working on it, and the best guess is that it’s a virus. But no one has completely narrowed it down.

Is there a link to climate change?

Temperature does matter. We definitely noticed that the number of sick sea stars quieted down last October and over the winter. Over the summer, the numbers grew again. But in terms of a specific trigger, it doesn’t seem like climate change is necessarily to blame since the summer of 2013 wasn’t unusually hot. But seasonally warmer temperatures could be a factor in the spread of the disease.

How does the loss of sea stars impact ocean ecology?

Sea stars are incredibly important ecologically. For example intertidal sea stars are voracious predators of mussels. If you take the sea stars away, the mussels overgrow many other species. As go the sea stars, so goes the shore.

Is there an end in sight to the current epidemic?

I’m very curious to see what will happen over the next 12 months. I’ve got sites around Vancouver that I sample in the winter, because the populations go into deeper water in the summer. Last winter, of the five sites I keep track of, four looked totally fine, and the other had gone from about 1,100 sea stars down to just one. We’ve since gone through a full summer, and more potentially vulnerable populations may have been hit. The good news is that there are reports of lots of juvenile sea stars around. That suggests that the little sea star babies have more food to eat, because the larger sea stars are gone. Hopefully, this is a sign that the populations are rebounding. I’m optimistic that they’re going to come back.

Chris Balma
c 604-202-5047