animals, bizarre, disease, human impact, microbes, oceans

Millions of Dead Sea Stars

I hesitated writing about this story because researchers really do not seem to know at all what is causing this catastrophe, yet, but doing science is primarily about solving mysteries – it’s really part of the scientific process. What exactly is the story? As you may have heard, potentially millions of sea stars (also known as starfish) have died along the Pacific Coast of North America since last summer, when mass mortalities were first found. And while researchers have some good ideas that may explain why this is happening, there’s no hard evidence to support any of them yet. The baffling, devastating condition has been termed the Sea Star Wasting Syndrome (or Starfish Wasting Disease) (giving it a name likely makes us feel like we understand it better than we actually do).

sunflower starfish Pycnopodia helianthoides seastar
The sunflower sea star (Pycnopodia helianthoides) has been one of the species devastated by the mysterious disease in the affected areas. (Image credit: Ed Bowlby/NOAA)

While we don’t know yet what’s causing it, we have a pretty good idea of what a sea star looks like that has Sea Star Wasting Syndrome. First, white lesions appear on the sea star. As these white lesions spread on an arm, the arm deteriorates and eventually falls off (and may continue moving for a little while after becoming detached). The sea star usually dies soon after its legs fall off, which can be just a few days after the lesions first appear. Sick sea stars are often seen with contorted legs that are pulling the body apart. The sea star’s guts may also spill out of its body through holes in its tissue, which has become softened and is basically disintegrating. With such a horrific description, it’s not surprising that this condition has a 95% mortality rate.

Several species of sea star have been found to be affected by Sea Star Wasting Syndrome, but the ones most impacted seem to be the purple sea star (Pisaster ochraceus) and the sunflower sea star (Pycnopodia helianthoides), which can reach more than a whopping one meter in diameter. Sea stars in the waters around British Columbia and Washington state (specifically Puget Sound) have been hit most heavily, as far as researchers can tell. However, similarly sick sea stars have been found in other areas along North America’s Pacific coast, ranging from Alaska to San Diego, California. They’ve been discovered in the wild as well as in captivity (in museums and aquariums). To help researchers keep track of the spread of the disease, a citizen science project is asking people to take pictures of sea stars they find in the wild and use #sickstarfish when sharing the images online.

The current leading hypothesis is that some kind of pathogen – a parasite, bacteria, or virus – is infecting the sea stars and weakening their immune system. While what this pathogen is remains a mystery, it’s thought that its infection leaves the sea stars vulnerable to other infections. Most of the damage done to the sea stars may then actually be due to this secondary infection. (The syndrome is almost certainly not caused by radioactive water leaked from the Fukushima nuclear power plant.) It’s possible that increasing water temperatures may also be playing a role, but this seems less likely since sick sea stars have been found in colder, Alaskan waters as well.

Since sea stars are predators (they eat mostly mussels, clams, barnacles, snails, and other animals), the loss of these animals from an ecosystem will likely have significant consequences. Everything below them on the food chain will be affected.

One lesson this has taught us already is the importance of paying attention to animals we may easily overlook. While we can clearly see there are massive die-offs of sea stars now, it’s difficult to compare this to normal mortality rates since they’re usually not closely monitored in wild sea star populations.


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