Marine diseases, sea stars, and why it might matter

A sea star that I found on a collecting trip in September.

 It's deep winter here, the kind that has us shoveling new snow more days than not and the animals on the beach dealing with all sorts of ice and snow, so I have more time for the blog than at other points during the year. It reminds me of my childhood winters elsewhere in the country much more than a normal winter here on the coast. So hi again. This time with content.

There are several conservation issues in the marine realm that make the news with some regularity. Climate change, of course, and overfishing, and the relative new kid, ocean acidification. But the latest issue that's making headlines is a catastrophic decline in sea star populations along the Pacific coast of North America. This decline is sudden and unexplained, and although the evidence is consistent with a disease, no one really knows yet just what that disease might be.

Yes, marine invertebrates get diseases too. Scientists really know very little about what causes diseases in the marine realm, but we do have examples from coral, lobster, and oysters, just to name a few. It seems like we need to add sea stars to that list. There's even some indication that the frequency of diseases has been rising of late, possibly due to changing climates.

Here are links to places around the web that have explained the current sea star issue better than I can:

PBS recently produced a great clip on News Hour about the problem that I strongly encourage you to see. The scientists interviewed here are ones that I have met and interacted with, and people I really respect. It's neat to see them on TV. In fact, one of them has made a previous appearance on this very blog for her work curating the collection of glass invertebrates at Cornell University.

More scientific information is available here from UCSC.  This site shows you the different stages of the disease, and even includes a form for you to report sightings of diseased sea stars (for anyone who might be reading this in the affected Pacific Coast area).


And lastly, here's another great blog post about the subject.

But why does any of this matter? Well, for one thing, sea stars are a group of marine animals that people feel some sort of connection to. They are iconic images of the sea, popping up in jewelry, home decor magazines, and children's cartoons. But they are also important animals in the communities where they occur. Six months ago, I wrote about intertidal zonation on rocky shores. Sea stars are crucial players in keeping mussel beds under control by eating mussels (the stars are pretty voracious predators). In fact, they are the defining example of a keystone species: one that has a disproportionate effect on the community relative to its abundance. Remove the stars from an area, and the whole community structure will change.

So the disappearance of stars due to a mystery disease is pretty troubling. Hopefully scientists can at least figure out what is causing the decline while there are still sea stars left in some of these areas to save.

The underside of the same star. Note the tube feet that they use for moving around (operated by a hydrostatic skeleton) and the mouth of the organism, which is in the center where all of the arms converge. Sea stars eat by ejecting one of their stomachs and digesting their prey before ingesting it.

In the bleak midwinter

My field site under six inches of snow.

The high tide line becomes easily visible in the snow: it is where the water has washed the snow away. The beach itself looked normal, until I looked closely.

Ice in the intertidal. It wasn't even that cold this morning (right around freezing). The local flora and fauna are frequently affected by ice in this area, which will scour the rocks bare and create new habitat.

It was beautiful this morning, above freezing, sunny, and not windy. A nice break in what is promising to be a very snowy week. Conveniently (since I need the snails), this corresponded to a very low spring tide. Because many of my snails have been frozen off the rocks (see the third picture) I had to venture out into deep enough water that the snails had not been frozen yet this winter.