A plague of stars

And I don’t mean plague as in “too many stars to know what to do with,” but as in “disastrous sickness that you don’t want to catch.” Some of the stars in my seawater table have been succumbing to some awful disease lately. A week ago today I noticed that many stars had been busy cannibalizing one of their compadres. Sometimes this just happens, and it doesn’t necessarily indicate that things are about to go south. But when I looked more closely I noticed that the victim, instead of just being eaten, had autotomized its arms. Autotomy occurs in most sea stars and other invertebrates, and in fact is used as a method of clonal replication in some stars and many cnidarians. The species of star that is being affected by this plague (Pisaster ochraceus, the common ochre star) isn’t one that readily autotomizes except in response to some external stress, such as a predator pulling on an arm.

So something was going on in this table. On Monday (Labor Day) I popped in for a quick check and although nobody had lost any arms I couldn’t be absolutely sure that everything was okay. Some of the Pisasters were a little squishy and had arms that were a little twisted. On Tuesday morning there was no autotomy but in the afternoon a star had lost an arm, greatly disturbing the student lab assistant who discovered it. On Wednesday the table looked like an asteroid battlefield:

Large Patiria miniata (bat star) scavenging on dead Pisaster ochraceus (ochre star)

Large Patiria miniata (bat star) scavenging on dead Pisaster ochraceus (ochre star).
Photo copyright: Allison J. Gong 2013

Many of the other Pisasters were also showing signs of sickness: curly arms (visible in the yellow star in the lower right corner of the photo above. Another ominous sign is that some of the apparently sickly stars were kind of squishy, indicating that the water vascular systems were somehow compromised.

Severed arms littered the table.┬áThe autotomized arms retain mobility for quite a while after being cast off–they literally don’t know that they’re dead.

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Autotomized arm of a sick Pisaster ochraceus. The other, intact, star is Orthasterias koehleri, the rainbow star.
Photo credit: Allison J. Gong 2013

After removing the corpses and cleaning the table as best I could I was able to take a closer look at the survivors. I noticed that most of the remaining Pisasters had twisty or crossed arms, and some showed pretty severe stretching in an interambulacral area (“armpit” area between adjacent arms), which I think is the first stage of autotomy.

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Pisaster ochraceus stretched interambulacral area, pulling its own arm off.
Photo credit: Allison J. Gong 2013

The disease progresses very rapidly, and within an hour a star in this condition had pulled off one arm and was working on another.

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Pisaster ochraceus that has autotomized an arm. Injury site is visible as a white area in lower edge of central disc. The autotomized arm is located at the top of the photo.
Photo credit: Allison J. Gong 2013

Unfortunately, this disease also affects other species. My Orthasterias koehleri (rainbow star) decided to join the fun. When I arrived Wednesday morning it was intact. It dropped an arm, I went away for about 40 minutes to take care of tasks in a different building, and when I returned it had lost two more arms:

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Orthasterias koehleri that dropped three arms in about an hour. The autotomized arms are indicated by yellow arrows. The remaining 2/5 of the star are attached to the outside of my urchin tank.
Photo credit: Allison J. Gong 2013

Alas, my one and only Orthasterias succumbed later in the day and was dead on Thursday. Interestingly, the disease does not seem to affect either Patiria miniata (bat stars) or Dermasterias imbricata (leather stars). In fact, the Patiria have been eating pretty well over the past week, scavenging on the carcasses of the plague victims. I don’t know if eating the diseased tissue will cause problems later on.

On Friday I lost two more Pisasters and isolated the Patiria and Dermasterias into tanks. A colleague of mine calls this the Molokai treatment, and I probably should have done it sooner, but I figured that at this point all the stars in the table were exposed to whatever pathogen is causing this disease so at that point why bother? However, I will need to sequester the healthy stars in order to disinfect the table once the disease has run its course, so into tanks they went.

After checking on the stars Saturday morning I am cautiously optimistic that the plague may have run its course. One more Pisaster, that was looking sickly the day before, had died, but my last two appeared healthy. Their arms were not curly, I didn’t see any interambulacral stretching, and they felt nice and hard when I poked at them. All of these are good signs, but I will continue to keep close watch on them. If they make it to Monday we just might be out of the woods.

As of today, one week after I noticed the first severe symptoms, I have lost 80% of my Pisaster collection. To put that in to context, this mortality rate is every bit as bad as some villages that were virtually wiped out by the medieval Black Death.

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10 Responses to A plague of stars

  1. EEE says:

    I’m sure you read your friend Chris’ article about the possible plague spotted off the coast of Vancouver a few weeks ago, and while I would hate to draw conclusions from two far-flung occurrences, this is a spooky timing. I hope things get better for your remaining five armed friends!

  2. algong says:

    Hi Eric (and yes, I know it’s you!)–Yes, I’ve seen Chris’ blog entries, and agree that it may not be a coincidence for wasting disease to have been recorded in the field and in the lab at the same time. If water temperature is part of the equation, we have indeed had warmer-than-usual temps at the lab–several uninterrupted weeks now of 16-17 degrees, which while not unheard of in the late summer is a bit unusual in my experience. So maybe that is a factor.

    I have one remaining 5-armed friend of that species. :(

  3. Amy says:

    The stars in our Sanctuary Visitor Center located in San Francisco all succumbed on October 1, 2013 (the day of the government shutdown). We are now doing some monitoring out in the field in collaboration with PISCO. See more information about the disease and the tracking and documentation of the disease along the entire coastline, http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/index.html.

  4. Dana Bagshaw says:

    We were discussing this at the Monterey Bay National Marine Sanctuary Exploration Center in Santa Cruz.

  5. pauline seales says:

    At Natural Bridges state marine reserve we never noticed diseased Pisasters but now they seem to be gone entirely from the visitor tide pool area

  6. algong says:

    Hi Pauline–I was down at Natural Bridges a few weekends ago and didn’t see any Pisaster at all. The tide wasn’t very low, but even where I was I should have been able to see stars along the lower edges of the mussel beds. Recently John and Devon Pearse did a more thorough search for stars at Natural Bridges and found only a handful or two. Whatever is causing this disease kills the animals very quickly, and they just seem to disappear. It is strange that, in a place that gets as much traffic as Natural Bridges, nobody seemed to see any sick stars….the stars are simply melting away.

  7. Genevieve Kurilec McDonald says:

    We are having very similar issues on the East Coast. Typically I wouldn’t make any comparisons due to the long distance between us but we’ve also seen a substantial decline in our sea star population.

    • algong says:

      I had heard that something similar was happening on the east coast, too. Did you happen to notice if the sea star population had gotten very large before the outbreak of wasting disease?

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