Courtesy kathleenreed via Flickr
It's a story that lends itself to hyperbole. An unknown disease causing the literal disintegration of a large group of animals across a wide geographic area. Sea star wasting disease has been on the minds of every marine science professional for the last two years. And amazingly...wonderfully, this issue has captured the attention of the general public as well. Through traditional media, the internet, and personal experience, sea star wasting has become, I think, the most visible issue facing the oceans today.
In case you haven't heard, throughout the North East Pacific, from Alaska to California sea stars have been dying off in large numbers. The animals begin to show signs of distress by curling their rays in unusual ways. Then white lesions (any kind of damage to tissue) appear on the outer skin. These lesions then disintegrate further until holes appear. Eventually the holes grow so large that limbs separate from their bodies, and the animals crumble into piles of skeletal plates. Some reports have stated that the disease causes the arms to walk away from the body, but that is a blatant exaggeration. Partly because stars don't have brains, their limbs can survive for a surprisingly long time after they've been separated from the central disk. So while the disease does cause the arms to come off, it's not what's causing them to keep moving. Sea stars can even deliberately drop off limbs in an attempt to protect the rest of their body from disease and predators. Then they grow a new ray in it's place.
"We can rebuild him, we have th...." "No that's okay he'll do it himself"
Courtesy Jill Siegrist via Flickr
So why can't the stars regenerate from the damages of the disease, and what the heck is causing it in the first place? Well for the last two years the answer has been a big, fat, "I dunnuh", but that's because researchers have been furiously looking into it, and good experimentation takes time. There has been amazing collaboration between aquariums, research labs, and everyday folks to study the spread and cause of wasting. From this collaboration a new study has identified a virus that is associated with sick stars.
Last year a team of researchers discovered the first virus associated with echinoderms. They found the pathogen inside the tissues of sea urchins on Hawaiian coral reefs. This virus was a type of densovirus which are most commonly found infecting arthropods, like crabs, shrimps, and insects. In the urchins the virus wasn't causing any disease, but as the outbreak of sea star wasting became more severe the scientists wondered if something similar might be at fault.
First they needed to see if there were any viruses in the stars at all, so the scientists separated virus sized particles from the tissues of sick stars and injected healthy ones with this material. They also boiled samples of those particles before injecting other healthy stars; doing so destroys the DNA that viruses could use infect the organisms. Sure enough the stars that received potentially active viruses became sick with wasting and the ones that received the boiled samples did not.
MMMM Nothing like a nice hard-boiled virus to start the day
Courtesy michelle@TNS via Flickr
From there the team ran a viral DNA analysis on the sick animals and found a densovirus that is unique to stars. They named the pathogen Sea Star associated Densovirus or SSaDV for short, and the more copies of the virus the stars were carrying the more likely they were to start wasting. Interestingly the team found that for most stars, the larger the animal, the greater the viral load, but the opposite was true for the sunflower star (Pycnopodia helianthoides). Sunflower stars were one of the first and most heavily impacted by the disease, so I'm curious if this association may have something to do with that. Through this, and some other lines of evidence, these researchers have found a compelling correlation between this virus and sea star wasting.
So is that it? Can we all wash our hands of this and get on with out lives? In short, no. The study confirms the existence of a virus associated with wasting, but it doesn't look at how the virus interacts with the sea stars' cells. It's extremely likely that the virus alone isn't what's causing the stars to die. Especially since the researchers looked at samples of stars collected as far back as 1943 and found the same viral DNA. And when you think about it that makes sense. When you contract a virus you don't get sick purely because the virus is in your body. You get sick because the virus combines with your stress from work, and the bacteria in your environment, and the fact that you stayed up late having drinks, to tax your immune system until it can't suppress the virus anymore and you get symptoms.
There has been extensive coverage of this study, but the problem is that many news outlets are claiming the answer has been found and they have ignored an important takeaway from the paper's conclusion. From the paper itself: "However it remains to be seen how infection with SSaDV kills asteroids, what the role is for other microbial agents associated with dying asteroids, what triggers outbreaks, and how asteroid mass mortalities will alter near-shore communities throughout the North American Pacific Coast." (Hewson et al. 2014). Essentially the author's are saying " this is a good start, but we have a lot to look into."
It's even possible that disease is a normal means for the
environment to handle overpopulation of echinoderms
Courtesy US Fish and Wildlife via Flicker
It all seems a bit bleak, but like I said before there has been an incredible amount of collaboration, and unprecedented visibility to the plight of West coast stars. Knowing the densovirus is associated with the disease won't stop it, but now we have jumping off point to further our understanding. This is a unique opportunity for you, as an interested person, to participate and keep this research alive.
So if I could ask one thing of you all it's this: Keep paying attention. Stay up to date, visit your local aquarium and ask questions, follow researchers on twitter. You can even go out and survey beaches for wasting stars yourself and scientists will use your data. Together we can develop a strong understanding, citizen and scientist alike, of what this disease is and does. So if you make statement about stars, or upload some pictures to social media I encourage you to attach the hashtag #RayOfHope, and we'll see if we can keep the momentum going.
For more information on the study that identified the virus check out this great summary from Ed Yong with National Geographic. Or read the paper yourself for free on the National Academy of Sciences website.
Hewson et al., "Densovirus associated with sea-star wasting disease and mass mortality", Proceedings of the Natural Academy of Sciences, Oct 2014, DOI 10.1073/pnas.1416625111