I've already written several times about seastar wasting syndrome (SSWS) and you've probably seen your share of photos of wasted, melting, self-mutilating stars. However, you may also be wondering about the current state of affairs regarding SSWS, and whether or not sea star populations have recovered at all since the outbreak began three years ago now. The question "How does SSWS affect the stars?" can be addressed on two different levels: the level of an individual star, and the level of the population of stars. In this post I discuss the first aspect, and in a subsequent post I'll share my observations of sea star populations in the field.
Level 1: SSWS as it affects individual stars
I remember very vividly the feeling I had when I opened the door to the wet lab and glanced into my table to see this:
And after that it only got worse, until (almost) every star was dead. It was interesting to watch how the disease manifests in different species of stars, though. The forcipulates--genera Pisaster (ochre stars), Pycnopodia (the huge sunflower star), Orthasterias (rainbow star)--succumbed quickly and violently. These were the animals that ripped their own arms off, often without showing any prior signs of distress, and then melted away.
On the other hand, other species seemed to be more resistant to SSWS. At least, they didn't succumb right away. Perhaps the disease (if it is indeed a disease) progresses more slowly in some groups of species compared to others. These stars, including the bat stars (Patiria miniata) and leather stars (Dermasterias imbricata), didn't rip their arms off. The only leather star in my care died about a week after the forcipulates bit the dust, and the bat stars seemed fine for months. And when these species got sick they showed different symptoms.
Instead of self-mutilation, the leather and bat stars developed lesions on their skin. The lesions could be very deep, exposing the animal's internal organs (guts and gonads) to the external environment.
The white objects inside the yellow circle are the star's skeletal ossicles, which have fallen away because the tissue holding them in place has been severely eroded. I haven't seen a leather star survive longer than a week once the lesions appear. Bat stars, on the other hand, can and do live for months with lesions. For example, this star of mine first developed lesions back in September 2015:
The lesions were small and superficial, and for a long time the animal didn't actually seem sick. It wandered around its table, remained sticky, and even ate. Now, seven months later, the star is still hanging in there. I took this photo of it yesterday:
The lesion is bigger and deeper and now the innards are exposed. The star is also a little deflated, which might be a bad sign. From what I've observed, once an animal can no longer maintain its internal turgor pressure, it probably can't recover. However, this one isn't totally deflated yet, so I still have hope for it. Heck, this animal has been sick for over half a year now and hasn't died yet. It obviously has some ability to resist the illness, or perhaps it's just dying very slowly.
Just for kicks I zoomed in on the lesion under the dissecting scope, and it actually looks sort of cool. It isn't every day that you can see the internal structures of an animal without cutting it open.
Sea stars don't have a lot of space in the central disc of the body, so they keep their gonads and guts in their arms. Each arm contains a pair of pyloric caeca (extensions of the gut) and a pair of gonads. In the photo above, the whitish ribbons are the pyloric caeca and the tan bits are gonad. Just for kicks I snipped off a piece of the gonad and looked at it under the compound scope. And lo and behold, it's a girl!
Those large round-ish blobs are oocytes in varying stages of maturity. I'm a little surprised to see any developing oocytes at all, given that this poor star has been sick for so long. Maybe this is a good sign. The internal fluid of the animal's main body cavity is essentially seawater, so having the gonads and guts exposed to the outside might not be the direct avenue to infection that it would be for us. From what I can tell the tissue itself looks healthy: it doesn't appear to be decomposing, the oocytes are full and more or less round, and there aren't a lot of ciliates swarming all over it. So I think there's hope for this animal, which has already survived so much, to pull through.
Another bat star that I've been keeping an eye on is a beautiful 8-armed star that was collected by Prof. John Pearse. Somehow I never managed to take a picture of this animal until it got sick about two weeks ago. One of the lab assistants noticed that it looked a little off on a Saturday, and two days later it had some nasty lesions.
Because this bat star went from zero symptoms to ulcerated lesions in two days, we didn't think it would last much longer. The lab assistants isolated it in a tub filled with 0.2-µm filtered seawater and have been changing its water daily. Just as it didn't take long for symptoms to appear, it didn't take long for this individual to show signs of recovery. About five days after first being isolated the star was sticking to the side of its tub, indicating that its water vascular system was still functioning. A week after that, I looked at it again and saw that the lesions seemed to be healing!
The surface of the lesion appears to be more solid, as if the epidermis had been knitted back together. There's still a bit of gonad exposed, though. Is this significant? At this point I'm not sure. The animal will remain in ICU, separated from all other echinoderms, until we are absolutely certain that it has recovered. And of course I may be jumping the gun to say that the animal is recovering at all. Only time will tell. It is, however, extremely refreshing even to think about SSWS without despair, for which I am grateful.