Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Sea Star Wasting Syndrome
Last updated Sept 21, 2016
Photo credits: Christy Bell (left), Rachael Williams (right).
Sea stars along much of the North American Pacific coast are dying in great numbers from a mysterious wasting syndrome. Similar die-offs have occurred before in the 1970s, 80s, and the 90s, but never before at this magnitude and over such a wide geographic area. Pisaster ochraceus and many other species of sea stars have been affected by the current sea star wasting syndrome event. The following 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 (SSWS) but there is still much work to be done before this mysterious disease is fully understood.
The first photograph in the below series of a sea star with wasting syndrome was taking on June 27th, 2014 on Guemes Island, Washington. The following picture was taken a day later, and the last picture, the day after that. These sequential photographs of a single individual demonstrate how quickly the disease can progress and the extent of damage that can be done in only three days.
Photo credit: Kit Harma
Over the past year, much of our effort has focused on documenting the progression of sea star wasting along the West Coast of North America and across a range of sea star species. That effort continues, however, we are now moving into a new phase in the assessment of sea star wasting: the ecological consequences from the loss of these species.
Sea star wasting syndrome is a general description of a set of symptoms that are found in 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. The proximal cause of the disease, when pathological studies have been done, is typically a bacterium (vibrio), although a recent wasting event on the east coast of the United States has been attributed to a virus.
The current bout of this wasting syndrome was first noted in ochre stars (Pisaster ochraceus) in June 2013 along the coast of Washington state during monitoring surveys conducted by MARINe researchers from Olympic National Park (ONP).
MARINe monitoring groups have since documented wasting in Pisaster ochraceus from Alaska through California (see wasting map for specific locations). Two common attributes for many of the sites are: (1) the period prior to wasting was characterized by warm water temperatures, and (2) the effects are dramatic.
The majority of early observations were made in intertidal (tidepool) habitats and as a result most of the early reports were for ochre stars, the most common in the habitat, but others species affected include the mottled star (Evasterias troschelii), leather star (Dermasterias imbricata), and six-armed stars (Leptasterias).
In August 2013, divers investigating subtidal habitats reported massive die-offs of sunflower stars (Pycnopodia helianthoides) just north of Vancouver, British Columbia. Shortly afterwards, other subtidal sea star species in the region began showing signs of wasting. During October and November 2013, a similar mass death of sea stars occurred in Monterey, California, with another die-off of sunflower and ochre stars around Seattle, Washington, with the syndrome spreading throughout the Puget Sound.
In mid-December 2013, substantial numbers of wasting stars were spotted around southern California. By the turn of the year it had been reported in 45 of the 84 MARINe sites from Alaska to San Diego sampled since that summer, and in the summer of 2014 it has spread to Mexico and parts of Oregon, which had previously been unaffected. It is also intensifying, appearing at additional sites in those regions already affected.
Photo credit: Nate Fletcher
In subtidal habitats, the sunflower star is typically the first species to succumb, followed by the rainbow star (Orthasterias koehleri), giant pink star (Pisaster brevispinus), giant star (Pisaster giganteus), mottled star, ochre star and sun star (Solaster), leather star (Dermasterias imbricata), vermilion star (Mediaster aequalis), six-armed stars, and bat star (Patiria miniata).
We don’t know whether the syndrome spreads sequentially from one species to the next, or if some species simply take longer to express symptoms, but the usually large populations of ochre and sunflower stars have experienced massive, geographically expansive (if patchy) and well-documented declines. Other species are less abundant, so the impact of the syndrome is not as clear.
From extensive samples collected researchers have begun to identify the agent behind the syndrome, and the environmental conditions that may have led to the outbreak. One of the top priorities is to confirm that an infectious agent is involved, and if so what it is. Molecular sequencing work of samples is underway at Cornell University to identify possible viruses and bacteria that could be causative agents. Current thinking is that there is an infectious agent involved, likely a pathogen. Importantly there is no evidence at all that links the current wasting event to the ongoing disaster at the Fukushima nuclear facility in Japan.
Ecologists consider both sunflower and ochre stars to be keystone species because they have a disproportionately large influence on other species in their ecosystem. In fact Pisaster ochraceus was the basis of the Keystone species concept because of its potential to dramatically alter the rocky intertidal community in which it occurs. Our long-term monitoring data, including population estimates prior to the Wasting event, in combination with our biodiversity surveys, will allow us to interpret change to communities that might result from severe population declines of P. ochraceus. The collected information will also be used to document recovery of both sea star populations and the community affected by way of the loss of sea stars.
Long-term trends in Pisaster ochraceus numbers at our monitored sites can be viewed by location here or by using our Interactive Map & Graphing Tool. Under "Long Term Graph Type" select "species counts data" and under "plot type" select "pisaster".
For more information about Sea Star Wasting Disease, please click here:
Our research group is concentrating on:
Documenting the presence of sea star wasting symptoms by means of submitted reports, our own sampling as part of MARINe Long-Term Monitoring, and our newly established Rapid Assessment Surveys of the outbreak.
Developing a spatial/temporal map of the outbreak showing the location of affected populations and (when possible) the onset of symptoms for each location. This will allow for an evaluation of potential hypotheses concerning the cause of the disease. For example if the outbreak started from a single location its cause is likely to be different from a situation where there were multiple initiation points.
Assessing the impact of the outbreak on the biological community.
Other research groups are addressing the pathology and infectiousness of wasting. These groups include Cornell (Harvell & Hewson), University of Rhode Island (Gomez), Brown (Wessel), Western Washington University (Miner), and Seattle Aquarium.
If you are interested in adding information to our Sea Star Wasting Syndrome Map, please see the options below.
Fill out the Sea Star Disease Observation Log
Please continue to submit observations after spending time diving or in the intertidal. We are constantly updating our website with the latest reports, and will update the map on a regular basis. Please remember to fill out a log even if you search and only find healthy sea stars, or no sea stars! This information is just as valuable as observations of diseased individuals.
Below are the different categories that we are using to document the stage of the disease. If you are interested in collecting additional information about sea star counts, sizes, and disease categories, please contact Melissa Miner and Rani Gaddam for details. We would like to increase the number of sites where long-term sea star data are collected, but in order to ensure data consistency, it is essential that a MARINe researcher is involved with initial site set-up and sampling.
Note that data submitted to us may be used by our research group for analyses, as well as by others who submit data requests to us. If you have any concerns about this, please contact us.