The humble sea star, beloved by many, symbol of tide pools, and... victim of a horrific melting disease? Yes. In fact, when it comes to sea stars, truth is stranger than fiction.
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| Healthy sea star |
- They have an eye at the end of each arm. You can actually see it if you look closely enough; it's a tiny little black dot. They don't see like you or I do, but they can sense light. If you close your eyes, turn towards the sun, and then wave your hand in front of your face, you can see the shadow of your hand passing over your eyes. This is a bit like how a sea star sees.
- Sea stars have to cling to rocks tightly so that they don't get tossed by the waves. In order to do this, they actually create a glue that sticks to the ends of their thousands of tiny feet. They also make a chemical that will dissolve the glue when they want to pick up their feet again. They can make and undo a glue that works underwater at will!
- Sea stars are voracious when it comes to eating mussels. In fact, they eat so many mussels that if they are removed from an area, mussels take over the rocks so that nothing else can live there. Without sea stars, tide pools fail to exist as we know them.
- The way that sea stars eat is like something out of a horror movie. When they find a mussel, they wrap their arms around it and pull from all directions until the mussel is too tired to stay closed and opens up. When this happens, the sea star spits its entire stomach outside of its body and digests the mussel inside of its own shell.
- Because sea stars eat so many mussels, they became early enemies of fishers. To try to get rid of them, fishers would drag them on the boat, cut them in half, and throw them back into the ocean. What they didn't know was that sea stars can regenerate, so by throwing the sea stars back into the water, they had actually managed to make twice as many sea stars!
So what's up with this wasting disease?
If you are a bit queasy, you may want to skip the upcoming pictures. What comes next is disintegration, decay, and ultimately death, but it is the last step to befall the ill-fated sea star that picks up this mysterious condition. On both coasts, sea stars are literally wasting away. One day they are perfectly normal, bumpy, slow moving animals eating mussels to their hearts' content. The next day, there might be a small lesion on the outside of the animal. The following day, it may have lost some of its legs. The following day, all of its legs may be walking around on their own, completely disconnected from the sea star and spilling their insides behind them. Next comes death. The entire sea star can literally fall apart within days, and yet we still don't know why. That's why this phenomenon is called Sea Star Wasting Syndrome (SSWS). A syndrome is a mysterious medical ailment for which we don't have a clear explanation or treatment. This syndrome is no joke either. Researchers examining one species of sea stars in southern California, Pisaster ochraceus, found that, in some of their study sites, 99% of the sea stars died. That is truly astronomical; it's a tiny, local extinction. While the west coast, stretching from Baja California, Mexico to Alaska, has been impacted most by SSWS, sea stars on the east coast of the US can get it as well.
If you are a bit queasy, you may want to skip the upcoming pictures. What comes next is disintegration, decay, and ultimately death, but it is the last step to befall the ill-fated sea star that picks up this mysterious condition. On both coasts, sea stars are literally wasting away. One day they are perfectly normal, bumpy, slow moving animals eating mussels to their hearts' content. The next day, there might be a small lesion on the outside of the animal. The following day, it may have lost some of its legs. The following day, all of its legs may be walking around on their own, completely disconnected from the sea star and spilling their insides behind them. Next comes death. The entire sea star can literally fall apart within days, and yet we still don't know why. That's why this phenomenon is called Sea Star Wasting Syndrome (SSWS). A syndrome is a mysterious medical ailment for which we don't have a clear explanation or treatment. This syndrome is no joke either. Researchers examining one species of sea stars in southern California, Pisaster ochraceus, found that, in some of their study sites, 99% of the sea stars died. That is truly astronomical; it's a tiny, local extinction. While the west coast, stretching from Baja California, Mexico to Alaska, has been impacted most by SSWS, sea stars on the east coast of the US can get it as well.
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| P. ochraceus with Sea Star Wasting Syndrome. Taken by Alisonleighlilly. |
This is not the first time that sea stars have wasted away. There were mass die-offs of sea stars in the 70's, 80's, and 90's, but nothing on this scale had been seen before. The current blight was first discovered in a survey of the sea stars P. ochraceus in Washington state in 2013, although the disease affects many different species of sea stars. For a while, the cause of the disease was completely unknown, but in 2014 a team of scientists proposed that the disease was caused by a densovirus. The interesting thing about the virus is that it could be found in samples of sea stars collected in 1942, suggesting the disease may have been around for decades before this disaster.
So what changed? One of the leading theories is that temperatures in the ocean got really warm. Warmer temperatures can physically stress animals out, making them more likely to get sick, and ocean temperatures were unusually high in many areas where the outbreak of SSWS was most severe in 2014. Scientists in the lab also saw that adult sea stars in warmer water died faster than sea stars in colder water. In addition, young sea stars were more likely to get sick in warmer water.
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The disease can first appear as lesions, followed by legs that fall off of the main body, leaving gaping wounds. The legs seem to have a mind of their own after, crawling around trailing innards behind them. The central circle of the body may be left, with the legs spreading to the far corners. When the pieces dissolve, all that is left are small, white spines, but not before the decaying arms of the sea stars have left a bitter, rotten smell behind.
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However, this doesn't explain everything. One study found that decreasing water temperatures could help sea stars live longer, but it didn't necessarily stop them from getting sick. Another study looking at the original outbreak in 2013 found that water temperatures were not particularly warm when the disease first emerged. Another theory was that if there were a lot of sea stars densely packed together, they would be more likely to get sick, but a lot of the places hit hard by SSWS did not necessarily have a lot of sea stars to begin with. Finally, although SSWS may be caused by the densovirus, there still isn't conclusive evidence that that is the cause. This leaves scientists with a pile of questions and very few certainties on which to build a plan for protecting sea stars.
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| The arms can dissolve at different rates. This arm was still moving, but you can get a good view of the circulatory system. |
The picture I just painted looks very grim, but there is actually a lot of reason for excitement and optimism. In a recent study, scientists found that the number of new sea stars that survived each year increased 74-fold between 2012 and 2015. In addition, there seems to be a genetic shift in the population to sea stars that are more resilient and don't get the disease as easily. Basically, the disease killed off sea stars without this genetic resilience, but the sea stars that survived produced new, hardier sea stars. It's a wonderful example of nature adapting. In a time of rapid global change, it is heartening to see some things becoming more resilient as opposed to wasting away.
