By Kristin Foss
Imagine a mysterious disease invading a community and targeting key members by quickly causing the body to literally “waste” away into slime! Sounds like a terrible science fiction flick, right? Instead, this bizarre “wasting” epidemic is plaguing sea stars (asteroid echinoderms) along the North American Pacific West coast. From Alaska to Mexico, sea stars are dying in large quantities and essentially devouring themselves.
What exactly is happening to the starfish?
Coined the sea star wasting syndrome (SSWS), the progression of this mysterious disease will literally cause a sea star to “waste” away in a matter of days. Sequential photos of infected sea star individuals reveal that the illness progresses and destroys the body in a period of three days. Typically, lesions develop on the ectoderm (outside tissue) of the sea star, leading to the decay of surrounding tissue, fragmentation of limbs and eventual death. Other symptoms include behavioral changes such as reduced body movement, limb curling and deflation.
In the 1970’s, 80’s, and 90’s similar die offs occurred, but the current outbreak is unparalleled. According to the Pacific Intertidal Monitoring Project at the University of California Santa Cruz, the first case of this episode of wasting syndrome was observed in June 2013 in Olympic National park on the coast of Washington State, where ochre stars (Pisaster ochraceus) were notably degrading and dying off. By 2015, at least 20 species of sea stars have been affected by the sea star wasting epidemic. Due to the extensive geographical spread and number of individuals infected, this episode of SSWS might be the most prolific marine wildlife disease to date.
Scientists have observed certain species succumbing to the disease first in subtidal habitats, said Melissa Miner, an associate specialist with the University of California Santa Cruz and the Pacific Intertidal Monitoring Project. “The sunflower stars (Pycnopodia helianthoides) are nearly always first, [followed by] various species of the ochre sea star, Pisaster,” Miner said. “But the bat star, Patiria, seems to be affected much later, and to a lesser degree. We still don’t have a lot of data on the progression of other species.”
With this disease targeting sea stars, it’s plausible that this illness could affect other species of the phylum Echinodermata. But at this point all evidence points to it only affecting sea stars, Miner said. However, in southern California, the populations of sea urchins have also recently declined due to a mysterious disease. “But the water has been extremely warm [in those areas],” Miner said. “And their declines could very likely be due to something other than SSWS.” Due to the lack of information about this mysterious syndrome, it’s difficult for scientists to identify the culprit.
What are the ecological consequences?
The issue is particularly troubling to many scientists as sea stars are often regarded as keystone species. A keystone species is an organism that plays a crucial role in the balance and way an ecosystem functions. Often, the removal of keystone species can disrupt the balance of other species, causing the entire ecosystem to dramatically alter.
For example, in 1969 researcher Robert T. Paine designed an experiment where he removed one species, Pisaster ocharaceus the sea star, entirely from a subtidal habitat. As a result, the complete removal had a huge effect on the surrounding organisms and ecosystem. Mussels are the major prey item for sea stars in this environment. With the sea stars removed, the mussels overpopulated the system and crowded out other species, completely changing the balance of the ecosystem. In ecosystems affected by SSWS, scientists believe both sunflower and ochre stars to be keystone species. Due to their large influence on other organisms within their ecosystem, these species have the potential to alter the rocky intertidal community they inhabit.
What is causing the disease?
The cause is still a mystery. But researchers are working to identify the agent and additional environmental factors causing the wasting syndrome. According to the Pacific Intertidal Monitoring Project, the top priority is to find out what the agent is and why it’s causing sea stars to waste away. Previous hypotheses of historical mass sea star deaths include storms, large temperature changes, starvation and even pathogens. In the fall of 2013, all major aquariums along the Pacific West Coast noticed mass mortality of captive sea stars. A majority of the aquaria water comes directly from the ocean, and scientists noticed that seawater treated with UV light did not spread the SSWS compared to untreated aquaria. This led scientists to think that the disease might be caused by a viral, microscopic pathogen in the water rather than environmental conditions.
A recent study identified the culprit in the case of the rising sea star mortality: a densovirus. A densovirus is a virus from the family parvoviridae. Through a series of laboratory tests and field observations, researchers concluded that SSaDV, a sea star associated densovirus, is present in high quantities in infected sea star tissue. This specific densovirus has been detected in both sediment and plankton, both providing a medium for the spread of the virus. By testing museum specimens from the early 1940s, researchers discovered the SSaDV might have been present in the waters of the North American Pacific Coast for over 70 years. Due to the research and observations, the densovirus provides the most promising culprit responsible for the wasting sea star syndrome at the moment. But why now? And why is it causing a mass mortality event? More research is needed to understand other factors contributing to the epidemic, and how scientists can help protect these key species.
What can you do to help?
The Pacific Rocky Intertidal Monitoring Project encourages the public to submit observations after spending time diving or tidepooling in these rocky interdidal areas. “We don’t know enough yet about the cause of the disease, so we can’t make suggestions for how [the public] might help in terms of decreasing disease prevalence,” Miner said. But people can submit their observations for both sick and healthy sea stars on the website seastarwasting.org. “These observations are posted to our SSWS tracking map and have been very useful for knowing where the disease is emerging and spreading,” Miner said.
If you like beer, you can help out in a different way. Rogue Brewery created the Wasted Sea Star Purple Pale Ale to raise awareness about the epidemic killing millions of sea stars. To support the effort, the brewery donates a portion of the proceeds toward Sea Star Wasting Syndrome research conducted by the Interdisciplinary Studies of Coastal Oceans (PISCO) at Oregon State University. This unique industry-academia partnership aims to educate the public about the largest marine animal disease as well as supports crucial research.
There is a glimmer of hope as some of the sea stars with the wasting syndrome are bouncing back. “We do see individuals that have lost arms due to the Sea Star Wasting Syndrome, but are currently healthy with arms re-growing,” Minder said. However, these cases in both the clinical and wild settings are still rare.
If you would like to learn more about the Wasting Sea Star Syndrome and current research, explore seastarwasting.org.