Although the last thing that any of us marine invertebrate biologists want to see again is a wasted sea star, the syndrome has once again been making its presence felt at the marine lab. It has been almost two years since I documented the initial outbreak, and while nobody is convinced that it has entirely run its course, most of us, myself included, had thought that perhaps the first wave had passed. Then, back in March of this year, I saw one of my stars doing this:
Those large white blotches on the aboral surface are open wounds, or lesions, through which some of the animal's innards are protruding. The arm towards the top of the photo has also begun dissolving, literally wasting away into the environment. The lesions eat right through the epidermis, liberating the skeletal ossicles that lie underneath it; I've circled two of them on the right side of the photo and there are two more at the bottom.
The discovery of this wasting animal was alarming and for a while I held my breath whenever I check on stars at the lab, but after several weeks of not seeing any additional sick animals I relaxed my guard and concluded the incident was a one-off. So imagine my horror to walk in this morning and see this in one of my tables:
Sea stars generally don't just lie on their aboral surfaces, and this animal was making no attempt to right itself. See how the margin between the arms is a little wavy? That isn't normal, either, and shows that the animal's ability to regulate its internal water content has been compromised. And while bat stars routinely scavenge by extruding their stomachs through the mouth and digesting whatever it comes into contact with, they don't leave the stomach hanging outside the body when they aren't feeding.
All of which gave me a bad feeling in the pit of my own stomach, which only got worse when I turned the animal over:
The animal appears deflated and has small lesions all over its aboral surface. I was feeling a little deflated myself when I saw this. With stars it can be difficult to determine just how alive (or how dead) an individual is. This one didn't fall to pieces when I picked it up, which didn't exactly surprise me because Patiria is less prone to losing its arms via autotomy than the Pisaster species (ochre, short-spined, and jewel stars) and Pycnopodia helianthoides (sunflower star), in whom one of the symptoms of wasting syndrome is a violent ripping off of one's own arms. I suppose this makes the whole episode marginally less horrific than when I saw my Pisaster stars wasting, or maybe I've become jaded.
In any case, I had to decide what to do with this sick star. It was in a table with half a dozen other bat stars, so whatever it was exposed to or was itself exuding has already been spread to the others. I couldn't leave it there to rot in place, but neither did I want to throw it away if it was still somewhat alive. I turned the animal so it was oral-side-up again and left it alone to see what would happen. If it righted itself I'd assume it was more or less alive and isolate it in a quarantine tank; if it didn't, then all hope was lost and it could be tossed. When I was ready to leave the lab several hours later, it was in the exact same position. Verdict: dead.
So, why now? I've been thinking about this, and here's what I came up with. The densovirus that has been linked to sea star wasting syndrome is always around in the environment. Like other opportunistic pathogens it doesn't usually cause a problem until a host organism becomes stressed or compromised. For the past two years we've been aware of wasting events up and down the coast, which wiped out the most vulnerable individuals. Animals with resistance, however, were able to survive. The survivors may have been weakened, though, and the mild El Niño of 2014 and the much stronger one we have now in 2015 have resulted in water temperatures much higher than normal. I haven't plotted the data yet, but in June and July the water temperature has been hovering at 15-16°C, with jumps this week up to 18.5°C over the past couple of days. These warmer temperatures can be very stressful to animals, which may be just what the densovirus needed to "announce [its] presence with authority" (that's a quote from my favorite baseball movie, Bull Durham). Outbreaks of wasting syndrome are probably caused by a combination of factors: population density of the host animal, presence of the densovirus, overall health of the host, water temperature, water chemistry, and others I haven't thought of. We are certainly not close to a complete understanding of this phenomenon.
At this point I don't have many stars left in my collection. I hope I get to keep them.