Seeing as today is the third anniversary of the first blog post I wrote about sea star wasting syndrome (SSWS), I thought it would be appropriate to take inventory of my remaining stars and see how they're doing. Right now I have custody of ~10 bat stars (Patiria miniata), 7 ochre stars (Pisaster ochraceus--collected last year for the juvenile survival experiment I did with Scott), and 1 Mediaster aequalis. For whatever reason the M. aequalis hasn't been affected by SSWS so I'm going to disregard it for now. Of the 10 or so bat stars, four live in one of my seawater tables, roaming free-range in quite a large volume of water. The other half-dozen or so live in a tank in a different building. The Pisasters live in 1s and 2s in tanks distributed in two rooms in the same lab.
After the initial horror and shock of the spectacular onset of SSWS, in which we watched stars rip themselves into pieces right before our eyes, what we've seen has followed the standard epidemiology pattern. Any time a novel pathogen enters a population, the individuals that have no immunity or resistance are the first to die. The disease spreads rapidly through the population, wiping out all of these weaker individuals. However, not everyone dies. Even during the Black Death of the 14th century, the very fact that 1/3-1/2 of the human population died of bubonic plague means that 1/2-2/3 survived. Those survivors presumably had some degree of resistance to the disease.
At the same time three years ago that all of my forcipulate stars died, divers were noticing similar phenomena happening subtidally. It didn't take long for us to realize that Something Big was going on, which was eventually dubbed SSWS. Fast-forward three years and now I'm seeing healthy, hand-sized P. ochraceus in the intertidal again. These individuals are certainly survivors from the SSWS outbreak; they were likely small juveniles during the plague, and were able to come out of hiding and expand into open niches after so many of the adults died. Whether or not natural populations will recover completely remains to be seen, but as of right now things look promising.
About a year ago, having gone two years without showing any signs of being sick, one of my bat stars developed lesions on its aboral surface. It's the red star in the middle of that blog post. This star is one of the four that live in my shallow table. It has now been sick for a year. See how it has changed since then:
The lesions have all gotten worse--the largest is about 2 cm long now--and the body margin has some ripples that it didn't have before, but the star is still alive. For a while it wasn't eating, as far as I could tell, but two days ago I watched it eat a piece of fish. Perhaps the return of cooler water is helping this animal survive.
One of its tablemates, however, hasn't been so lucky. I first noticed apparent SSWS damage in a second star several months ago. Today was the first chance I had to look closely at it.
The most noticeable injury to this star is that big interradial divot. It looks like someone took a bite out of the body at that spot. The margins of the wound are white and fluffy, similar in appearance to the lesions caused by SSWS.
For years now this star has had an abnormal spot on its aboral surface. I've been calling it a bubble, for lack of a better word. The bubble may be an over-inflated papulla (skin gill) and it didn't seem to be causing any problems for the star. I'd touch it and it would deflate, then re-inflate almost immediately. When I touched it today, it shrank back a little but didn't really deflate.
If you look really closely at the above photo, you can make out clusters of small, clear, clublike projections. These are papullae, extensions of the internal body lining that project through the skeletal ossicles to the outside and act as gas exchange surfaces. The bubble is many times larger than the normal papullae. Because it has been there for so long, years before the divot in the interradial margin, I don't think the bubble is due to SSWS. I don't even know if it's a wound, or merely an overinflated papulla. The largest star in this table has also had a bubble for many years, but no lesions or wounds indicating SSWS or other disease.
So. Three years after the outbreak of SSWS I still have stars that are sick. They've been sick for a long time and aren't getting worse very quickly, from which I conclude they may eventually recover. At the very least they must have some resistance to the SSWS pathogen because they've managed to survive so far. One more thing. Way back in 2013 when all of the forcipulates were tearing themselves into pieces and melting into piles of goo, these bat stars were among them, scavenging on the dead and decaying tissue. For a while I feared that eating contaminated tissue might cause the disease, but that doesn't seem to be the case, as these two didn't get sick until two years after the initial exposure.
I hope these two stars make it. Cooler water temperatures should help. When they're really sick they stop eating (they haven't eaten much in the past year) but if they're going to eat now I'll keep feeding them. Fingers crossed!