Starfish Wasting Disease!

UPDATE: you can now upload YOUR pictures of starfish wasting disease. They are being tracked at this website (iNaturalist)

Last week I reported on an unusually large die-off of the North Pacific sunflower star, Pycnopodia helianthoides (among other starfish species) in the waters of British Columbia. The story even got picked up by National Geographic!

This sparked some good academic discussion here which I can only hope will lead to some further insight into what is happening.  One useful thing which came up was the mention of something that would be a good follow up to last weeks' report:  Starfish Wasting Disease!

I have spoken of ciliate protist parasites in sea stars before but this is something different.

Details of the post today about Starfish wasting disease is based on this paper in the journal, Diseases of Aquatic Organisms from an article by Amanda Bates, Brett Hilton and Christopher Harley in 2009

Other information is from an account of starfish wasting disease in the Channel Islands by Ginny Eckert and colleagues. This paper is freely available here.

I should also mention that my friend and colleague Dr. Allison Gong has documented an outbreak of wasting disease in her water table at UC Santa Cruz. I've borrowed many of her pictures below. My thanks to her for allowing me to use them! 

What is Starfish Wasting Disease? 
Symptoms of the disease are relatively straightforward:

1. White colored lesions appear and grow rapidly
2. There is a loss of body pressure (i.e., turgor)
3. Body disintegration and autotomy of arms, etc. 
4. and finally death...

Bates nicely outlines the various stages of the disease in her paper focusing on Pisaster ochraceus, the ochre star.

Fig. 2 from Bates' et al. 2009

Allison Gong recently documented these symptoms in her blog

Lesions...

followed by decay and autotomy (i.e., arms begin to shed..)

The effects DO seem very similar to what happened with the Pycnopodia die-off

fr. Jonathan Martin

But what actually causes the disease?? Sadly, we are just beginning to understand it and so we don't actually know WHAT the causative agent is.  Molecular tests for bacteria haven't confirmed anything.
Could it be a virus? A fungus? Some strange combination thereof?

Its also unclear if it is the SAME agent at work in EVERY case. Different species? Different strains? Different diseases?

The symptoms of the disease have been documented widely: on the west coast of North America. From British Columbia down to the Gulf of California. But also in the Mediterranean and the North Atlantic coast of North America.

Nothing yet from the Southern Hemisphere.. Australia, New Zealand, etc.

What Species Does It Affect?
Wasting disease appears to be pretty widespread across MANY starfish groups. 

The symptoms of the disease have been observed as early as 1972 from the east coast of North America in the "common" starfish Asterias vulgaris (now called Asterias rubens, pic on the left)

In 1982, there was a mass die-off of Heliaster kubiniji in the Gulf of California, which was so severe that it led to local extinction in several areas where it had once been abundant. (Image of Asterias by "misenus1", Image of Heliaster by manzanita-pct)

Eckert's account in the Channel Islands however, documents the widest spread where it was recorded affecting TEN species of most commonly occurring sea stars! Not to mention three sea urchins, two brittle stars, and one species of sea cucumber!

Disease outbreaks in these species resulted in die-offs and significant population declines.

In our recent example with Pycnopodia, which looks very much like wasting disease, we saw not just Pycnopodia, but also the sun star- Solaster dawsoni..(pics by Jonathan Martin)

Solaster dawsoni feeds on sunflower stars..

Similarly, Allison observed the bat stars, Patiria miniata feeding on decaying Pisaster ochraceus. Can the disease be conveyed as food? Will we start to see greater spread? 

But again, we don't know the actual agent of wasting disease. The symptoms might be something that happens in parallel as a result of several different agents.

Temperature! The Key to Wasting Disease
Eckert's paper speculated that warmer waters in the Southern California region accompanied the onset of wasting disease in the species they studied.

Amanda Bates & her team study studied Pisaster ochraceus in British Columbia and studied several variables and how they affected the disease. 


Indeed, temperature turns out to be a very important factor in the spread of starfish wasting disease! 

The graph below shows that the prevalence of the disease in starfish under experimental conditions is significantly higher under warmer conditions. This was also reflected by observations in the wild as they saw higher incidence of disease in the summer (June) than in August.

Figure 3 from Bates et al. 2009

One final and important observation that Bates and her team recorded was that the disease prevalence was higher in a protected inlet (GM=Grappler Mouth) versus an open wave-swept area (SB=Scott's Bay). 

This highlights another aspect: What aspect of starfish in the protected inlet vs. the open area to the higher infection rate? 

• Wave action? (and thus more current and temperature circulation)
• Freshwater input? resulting in higher vulnerability? (starfish don't tolerate freshwater very easily) Sewage? 

Aquaria, it was observed, also tended to show higher incidences of infection. 

So, it appears there seems to be a good correlation with wasting disease prevalence and infection strength with higher temperature. Also being exposed to open ocean conditions vs. more enclosed conditions..

Starfish Wasting Disease in the Big Picture

1. Global Warming. If this disease and the ciliate castration parasite are both temperature dependent and we are seeing an across-the-board increase in ocean temperature, this could have significant or even profound effects on populations.  

Higher rates of diseases and greater vulnerability to diseases affecting not just sea stars, but urchins, and other echinoderms could seriously impact populations of these species. 

2. Impact? Many if not all of these sea star species (to say nothing of the other possible echinoderms that could be affected) are what's called keystone species, that is, in an ecosystem their presence (or absence) represents a profound effect on many other species. 

Ochre stars for example affect mussels and other animals in marine ecosystems that cover rocky intertidal bottoms. Sunflower stars are a major predator of everything from snails to sea urchins, and sometimes other starfishes. 

Diseases like this can decimate or remove these ecologically important species resulting in unforseen results! Just consider this case about abalone and otters as one example..