|MARINe Leads Effort to Understand Sea Star Wasting Syndrome (SSWS)|
by Melissa Redfield, UC Santa Cruz, Melissa Miner, UC Santa Cruz, Long Marine Lab, Mary Elaine Helix, BOEM, and Lisa Gilbane, BOEM
Sea star wasting syndrome (SSWS) is a general description of a set of symptoms that are found in diseased sea stars. Typically, lesions appear in the ectoderm followed by decay of tissue surrounding the lesions, which leads to eventual fragmentation of the body and death. A deflated appearance can precede other morphological signs of the disease. All of these symptoms are also associated with ordinary attributes of unhealthy stars and can arise when an individual is stranded too high in the intertidal zone (for example) and simply desiccates. “True” wasting disease will be present in individuals that are found in suitable habitat, often in the midst of other individuals that might also be affected. The progression of wasting disease can be rapid, leading to death within a few days, and its effects can be devastating on sea star populations.
This current bout of this wasting syndrome extends from Alaska to Northern Baja California, affecting over twenty sea star species. Symptoms were first noted in ochre stars (Pisaster ochraceus) in June 2013 along the coast of Washington state during monitoring surveys conducted by Multi-Agency Rocky Intertidal Network (MARINe) researchers from Olympic National Park. The disease has seriously impacted ochre star numbers at nearly all MARINe long-term monitoring sites, with typical declines of around 80% at northern sites (hundreds of stars in permanent plots reduced to tens of stars), and nearly 100% at many southern sites (south of Point Conception). As of January 2015, signs of wasting have been observed at 98 of 137 MARINe sites sampled since 2013.
The tracking of SSWS began summer 2013, as MARINe was holding its annual meeting at the University of Washington facility in Forks, Washington. In response to discussion from that meeting, MARINe researchers at UC Santa Cruz quickly devised a protocol with detailed photos. This protocol was vetted and modified through discussion with other MARINe researchers and was added to the MARINe protocol for our established sites. Thanks to the MARINe network spanning the entire coastline of North America, the extent of the syndrome has been assessed using the same protocols, allowing for comparison of the extent of disease among sites. This assessment was possible because ochre star populations were sampled for many years, at some sites over 20 years, before the disease hit. Over 40 MARINe partners, representing multiple institutions such as universities, tribes, and government agencies at both the state and federal level, have been key in documenting the expanse of this disease.
Despite the large network of researchers involved in documenting the disease, gaps in spatial and temporal coverage are inherent with such a large stretch of coastline affected by SSWS. Citizen scientists and the general public have played a crucial role in helping to fill the gaps between long-term monitoring sites by becoming involved in a variety of ways. The majority of the interested public have contributed to the SSWS monitoring effort by submitting casual observations. These are often tidepoolers, surfers, and recreational divers who document their observations of disease and submit them to pacificrockyintertidal.org. This involvement requires no prior training so long as photographs are submitted for species and disease identification. For those desiring a more involved role in sea star monitoring, citizen scientist groups have formed and been trained by experienced MARINe researchers to set up and sample their own monitoring plots. Observations from all contributors can be seen on the SSWS tracking map on pacificrockyintertidal.org. This map is updated frequently with the latest observations. In addition to the map, protocols for monitoring, guides for species and disease identification, and updates about possible causes may be found on the website.
MARINe researchers were also involved in collecting sea star tissue samples for pathology work aiming to identify the cause of the syndrome. The recently published paper by Hewson et al. “Densovirus associated with sea-star wasting disease and mass mortality” provides evidence for a link between a densovirus (SSaDV) and sea star wasting syndrome. This is an important piece of the SSWS puzzle, but we want to stress that there is still much work to be done before this mysterious disease is fully understood. Importantly, Hewson’s testing of sea star tissue collected from as far back as 1942 indicates that the SSaDV has been around for a long time, yet has never resulted in mass mortality on the geographic or temporal scale we are currently witnessing. Thus, while a culprit may have been identified, we still don’t fully understand the cause. The complete story is likely a complex interaction of multiple factors, and may involve different factors in different regions. For example, the emergence of SSWS in some areas appears to be correlated with increased water temperature, but this does not apply generally across the entire west coast. Finally, the discovery that the SSaDV is present in other echinoderms which are not currently experiencing mass mortality, suggests that these species could serve as “reservoirs” for the virus that could continue to infect sea stars for many years to come. Disease symptoms and mortality have also been observed recently in other echinoderms such as sea urchins, though it is unknown whether the cause is related.
One possibly positive note is that at a few sites, a high influx of juveniles have been observed. Thus far, these juveniles have mostly appeared healthy, though it can be difficult to assess the health of such small individuals. It is unknown whether these juveniles will survive the outbreak of SSWS and grow to replenish populations, or will also become diseased like so many of their older counterparts. Monitoring by MARINe partners, other research institutions, and citizen scientists will track the possible recovery of sea star populations along the coast. To find out how sea stars are doing at a particular beach, go to pacificrockyintertidal.org and visit individual site pages or view long-term ochre star trends using the Interactive Map and Graphing Tool.