Commonly Asked Questions about Sea Star Wasting Disease When was sea star wasting disease first noticed? The first reports of sea star wasting disease were from summer 2013 (June) in the Pacific Northwest. The disease was then noted in Vancouver and central California in late August, Southern California beginning in November 2013, and finally in Oregon in summer 2014. Which sea stars is the disease affecting? The disease has been reported in over 20 species of sea stars, commonly known as star fish, from the Pacific Coast. It was first noticed in the sunflower star, Pycnopodia helianthoides ochre star then in the ochre star Pisaster ochraceus. What are the signs of the disease? There are a key set of signs associated with the disease, although they can differ among species. Typically sea stars will start to show uncoordinated arm movement (resulting in 'pretzeling', or curling up of the limbs). They will then typically take on a 'deflated' appearance and develop lesions on their arms or central disc, followed by disintegration of their external tissues. At this stage, internal organs may protrude out of lesion holes. Sea stars will then lose their arms, before 'melting', which means that their tissues disintegrate. Ultimately, the dead stars decompose, often associated with mat-forming white filamentous bacteria. These mats are frequently reported in areas where large numbers of sea stars have died, and are part of the natural decomposition process of any animal in the marine environment. Where is the disease currently? The current extent of disease is from Sitka, Alaska to Baja California. Scientists are performing extensive intertidal and subtidal surveys to fill in gaps where citizen science groups are not present to report incidence (such as in mid-Oregon). A similar event occurred in Forbes' sea stars (Asterias forbesii) in the Northeastern United States in 2012 and 2013 and mortality is ongoing. Have there been other events such as this? Aside from the previously mentioned mass mortality in the Northeastern United States, there have been other mass mortalities of Californian sea stars in the late 1970s, and in the early and late 1990s. The current event is by far the most spatially extensive event. Previous mortalities have been correlated to oceanographic phenomena, such as El Nino oscillations. This event is also distinctive in involving at least 20 species of West Coast sea stars. What might this mean for the ecosystem? Sea stars are considered a keystone species because small changes in their numbers can affect their prey species and the surrounding ecosystem. The two dominant sea stars affectedPycnopodia helianthoides and Pisaster ochraceus are important predators of bivalves such as clams and mussels in rocky habitats. But as a group, the twenty species of sea stars eat a very wide range of prey. As with the removal of any predator, there is a potential for the organisms that sea stars eat to experience unusual population increase, affecting other species. The effects of the current sea star mortality will be studied by scientists performing long-term monitoring at specific sites where sea stars have been observed for decades. In the short-term, sea star mortality leads to a large increase in organic matter in areas where they have died, which in turn fuels bacterial activity. One effect of this increased activity is the production of foul-smelling gases, such as hydrogen sulfide (rotten egg gas) in the vicinity of decaying stars. What is the cause of sea star wasting disease? Sea star wasting disease is associated with a densovirus that lead researcher Ian Hewson has dubbed sea star associated densovirus (SSaDV). This virus is similar to ones previously seen in tropical urchins, but different from all other known viruses infecting marine organisms. How did Hewsons team come to that conclusion? Through comparison of bacteria and eukaryotic microorganisms (e.g. yeasts) inhabiting healthy and diseased tissues, and histological observations of diseased tissues, the team ruled out those groups since no unique taxa were distinct to diseased tissues and no cellular microorganisms were observed in lesions. They then turned to viruses, since several lines of evidence suggested they may be involved in the disease, notably that the organism moved into research aquariums through sand filters and were eliminated by UV light. Through serially repeated inoculation of viruses from diseased tissues into healthy tissues, they determined that wasting disease was transmissible by a virus-sized organism. By then comparing the types of viruses in the healthy and diseased tissues they discovered the presence of a densovirus which we named the sea star associated densovirus (SSaDV). They then compared the

number of SSaDV copies in healthy and diseased stars and their prevalence (i.e. % in which they could detect SSaDV) and found that they were much higher in the diseased stars. Where did SSaDV come from? Is it new? The team examined the presence of SSaDV in preserved sea stars that were collected between 1923 and present, and could detect the virus in samples as old as the 1940s. Hence, SSaDV has been present on the West Coast for at least 72 years. We have also begun to study where SSaDV has its origins, if not on the West Coast. Work is underway to examine viruses in sea stars from many locations in 6 continents. If SSaDV is old, why is it causing disease now? Most viruses in nature maintain a low infection and disease rate, and it is only when their host organisms population surges, the host becomes stressed, or an easier or more frequent way for viruses to move between hosts that viruses will cause significant disease, or epidemics. Additionally, the virus itself could also undergo mutation to evade host defenses against infection. We do not yet fully understand why SSaDV has become a widespread killer of sea stars, but it is worth noting that in the Pacific Northwest sea stars were much more abundant immediately before the wasting disease event than in preceding decades, and different species succumbed to the disease in a sequence that mirrored their relatedness. These data points suggest that there may have been much better opportunities for the virus to move between hosts, and that SSaDV may be mutating to infect new hosts. How does SSaDV transmit between sea stars? Early observations from research aquariums suggested that the causative agent of wasting disease was able to move through the water, since they moved into aquariums through coarsely-filtered intake waters. We found that SSaDV is present in virus-sized particles free in seawater, and can also be found in sediments (sand) on which sea stars have walked. Experiments in the lab suggest that SSaDV can also transmit from direct contact between infected and uninfected individuals. Hence, SSaDV almost certainly transmits directly through seawater. Work is underway to understand how long the virus can be present in seawater by studying its decay rate in sunlight and in the presence of organic particles. Are other animals infected with SSaDV? We detected SSaDV in several other groups of echinoderms, the taxonomic group to which sea stars belong. These include urchins, sand dollars (a type of urchin), brittle stars and basket stars. It is unknown whether these cause mortality of other hosts. Can humans be infected by SSaDV? There are no known viruses of marine invertebrates that can infect humans. Most viruses can only infect within the same species of animal, and at most between related classes of animals. Echinoderms are only distantly related to humans and other mammals. Is SSaDV the cause of wasting disease on the East Coast? We detected an SSaDV gene in Forbes sea star (Asterias forbesii), however we do not have any information on whether it is involved in that sea stars demise. What institutions have been involved in investigating the cause? Collaborating with scientist Ian Hewson are other scientists from Cornell University, researchers from the Vancouver Aquarium, Seattle Aquarium, University of Washington, Western Washington University, USGS, UC Santa Cruz, Monterey Bay Aquarium, UC Santa Barbara, Wildlife Conservation Society, UC Davis, the LA County Museum of Natural History and the California Science Center are integral to the projects success. Contact: Melissa Osgood Office: 607-255-2059 Cell: 716-860-0587 Email: mmo59@cornell.edu Ellen Leventry Office: 607-255-2722 Email: eel2@cornell.edu