By Adria Magrath
A shorter version of this blog article appeared in the Christmas issue of the Vashon Beachcomber.
It seems that you can always count on seeing sea stars when you visit a rocky beach – the Pacific Northwest boasts the largest diversity and numbers of sea stars on the planet- but by most accounts, our local population is in a sudden precipitous decline. One four-year-old recently exclaimed to me “The sea stars are turning into mush!” Indeed, there is a current widespread outbreak of something called “sea star wasting syndrome” that quickly turns these iconic, amazing creatures into a puddle of rotten goo.
This is not the first time this has happened. The syndrome was first recorded in the early 70’s, with localized outbreaks occurring periodically ever since. However, it has never been this extensive in terms of geographic area and species. It was first observed on the East Coast this year, and Vashon Island claims the first recorded incidence on the West Coast. As of this writing, at least 10 species of sea stars are affected as well as a few closely-related animals in the same echinoderm family- like urchins and sea cucumbers. It has been seen from Orange County to Alaska, and from New Jersey to Maine, and in some places it is almost apocalyptic in scale
Symptoms of sea star wasting begin with white lesions and a loss of internal body pressure (turgidity). Because sea stars rely on hydrostatic pressure within its body tissues to function, this loss causes them to deflate and literally lose their grip. The disease progresses rapidly, and in a matter of hours individuals begin to disintegrate- arms fall off and crawl away on their own. Because the sea star literally falls apart while still living, some have coined it the “sea star zombie apocalypse.”
Although precise numbers are hard to come by, at this time, Washington, British Columbia and California seem to be the hardest hit, with populations in protected waters like Puget Sound and the Strait of Georgia in B.C. almost decimated, while areas exposed to open ocean wave action seem to be faring much better, A research station near Monterey Bay in central California found no evidence of the disease in mid-October, but by early November half of the most common sea star species were afflicted and the overall number of sea stars was lower than ever recorded in the 14 years of the station’s history. Some notable species had disappeared entirely. This is a shocking example of how fast this disease is wiping out entire sea star populations in certain areas.
Rayna Holtz, a Vashon Beach Naturalist, has been keeping records for a few years, and her data shows the numbers of sea stars at the same location change from two-dozen individuals in 2011, to 16 in 2012, to zero this year. Granted, there are normal annual changes in abundance and distribution, but finding absolutely no sea stars is unprecedented. Furthermore, on a December 3rd beach walk at the North end, a group of beach naturalists witnessed devastating carnage of dismembered rotting sea star arms littering the beach and the sea stars seemed to be melting off the dock pilings.
Scientists do not have an answer yet, and researchers around the country are studying the molecular nature of the disease, trying to identify whether it is caused by virus, bacterium, fungus, changes in water chemistry or, more likely, a combination of factors. Though much smaller in scale, previous sea star wasting events occurred in 1983 and 1997, with the most recent being in 2008. It is not clear if all of these events share the same causative agent, but studies of those events have strongly implicated warmer water temperatures associated with El Niño years. However, this year the surface waters of the Pacific Ocean have been reported to be colder than average. Interestingly, the wasting symptoms are typical to what ecologists observe in sea stars after stressful events like low-salinity, low oxygen or too-warm temperatures. Aquarium workers also report that these symptoms are typical when marine invertebrates get too stressed.
So is something physical in their natural environment stressing them out?
Ocean acidification is being investigated, but some experts discount it because acidification is pervasive, while the outbreaks seem more localized. The Seattle Times recently published a lengthy story on ocean acidification, and while their evidence was criticized by some experts, it is true that strong winds can pull deeper high-CO2 waters towards the surface (called upwelling) which can lead to temporary localized increases in acidification.
Although expert hypotheses abound, many in the lay public point to Fukushima. While a trending meme on social media, it seems pretty clear that radiation poisoning on such a scale would affect far more than just the echinoderm family. As of this writing there are no other diseased and collapsing populations. And while it is true that tests of carnivorous fish off the coast of Japan show increased radiation, those doses are still lower than the radiation dose in a single banana. The Washington State Department of Health has also been testing fish caught in our waters and has not found evidence of increased radiation.
Many ecologists also note that locations up and down the west coast saw a population explosion of sea stars in recent years and in much the same way dense stands of trees aid the spread of pine beetles, the relative glut of sea stars may have facilitated the severity of the current outbreak. Many experts think this may be an impressive example of the normal boom and bust cycle of natural populations – when naturally occurring pathogens can take hold in overabundant populations. Because sea stars have experienced this before and recovered, it suggests some sort of pathogen lies at the heart of the current mass mortality event, with stressful environmental conditions worsening the infection. Regardless of the cause, Vashon’s sea stars are wasting away before our eyes.
Would you like to help us keep track of our sea star populations? You can report both healthy and diseased sea stars to the Pacific Rocky Intertidal Monitoring Program: http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/
OR send a note on location, date, and photo if possible to Vashon Nature Center and we will report to the local and regional scientists for you: email@example.com
Thanks for your help!
Author Adria Magrath is a biologist, teacher, and Vashon Beach Naturalist.