Why Are So Many Starfish Dying? | National Geographic
From Mexico all the way to Alaska, there has been a massive die-off of sea stars. The estimates are in the tens to hundreds of millions of sea stars that have died in the last couple of years. It's one of the largest mortality events associated with a disease that we've ever observed in the ocean.
In this region, here in the Sailor Sea, there are almost 30 different species of sea stars. You can call it sea star or starfish; they're the same thing. So we've been looking at the effects of sea star wasting disease on populations of sea stars.
Today, we're going to go out and we're going to survey a population of sea stars on Whidbey Island. Several years ago, when we surveyed the population there, there were thousands of sea stars. But we'd had reports recently that individuals were starting to get sick. We’re interested in how that population has changed.
When we're swimming around at the site, we'd see just an arm dangling off a rock, no body nearby. Oftentimes, as sea star wasting disease conditions progress, an individual will be sitting there, and its arm just literally crawls away and rips away from the body.
In addition to that, we're seeing the kind of telltale sign of the disease, which is basically a pile of white goo that is the deteriorated remains of a sea star. We dove here several years ago; star covered the bottom and the walls, and we found less than 20 today. It's just depressing to see this.
One here is the okra star; it's kind of a common intertidal sea star that we have. It's the poster child of sea stars, I would say. You can see this species has five arms; it's missing one of those arms here. And you can see right here are the internal organs that are poking out from that particular wound.
One of the obvious signs of the disease are these white lesions, and that's where the tissue is starting to degrade. If we came back in a couple of days, we would find probably something that looked like this. You know, so this is the result of wasting disease.
To identify the cause of a particular disease is quite difficult, and it's even more difficult in marine organisms. The part that I had was collecting tissue samples. We normally send those tissue samples off to colleagues that will do further analysis, maybe sequence DNA or look at a composition of tissue underneath microscopes.
The work that was done pointed to a virus, a denzo virus, causing sea stars to not be able to defend themselves very well against microorganisms. We know so little about sea star wasting disease that that was a big step in our understanding of the disease.
One of the major concerns when you have a mass die-off is that all the adults, which are the reproducing individuals, are gone. As a result, you can't make new babies. So we were able to identify and observe a couple of juveniles at the site. It's always very encouraging to find the juveniles.
The hope is that those individuals grow up unaffected by the disease and can repopulate those sites.