Sea Star Wasting Disease

seastarwasting.org

Sea stars along much of the North American Pacific coast experienced a massive die-off in 2013/14 due to a mysterious wasting disease. The disease, called “sea star wasting disease” (SSWD) has persisted at low levels in most areas, and continues to kill sea stars. Similar die-offs occurred in the 1970s, 80s, and 90s, but never before at this magnitude and over such a wide geographic area. The ochre star, Pisaster ochraceus, the sunflower star, Pycnopodia helianthoides, and at least 20 other species of sea stars have been affected by the current SSWD event.

Recently, a paper by Prentice et al. (2025) identified a novel strain of the bacteria Vibrio pectenicida (named strain FHCF-3) as a causative agent of SSWD in sunflower stars. This multi-national, multi-disciplinary research team, led by MARINe partners at the Hakai Institute, used disease challenge experiments and genomic datasets to identify this bacterium as a causative agent. They confirmed V. pectenicida as a causative agent of SSWD by growing it in isolation in the lab and demonstrating that exposure to isolated V. pectenicida caused disease signs. This work also significantly associated V. pectenicida with an outbreak of SSSW in sunflower stars in the wild, providing additional evidence for this pathogen as a causative agent. In addition, the authors identified V. pectenicida in sequences from sunflower star tissue samples collected in Alaska in 2016, when SSWD was first advancing into this region, suggesting that this pathogen was present during the initial spread of the epidemic.

More research is needed to (1) investigate V. pectenicida as a cause of SSWD in other species, (2) identify additional strains of V. pectenicida associated with wasting sea stars along the Pacific Coast of North America, and (3) characterize the association between temperature and SSWD with respect to V. pectenicida. Another key question is whether reservoir species exist for this pathogen (i.e., species that may harbor the pathogen without exhibiting disease signs or experiencing mortality). Indeed, existing strains of V. pectenicida have been isolated from moribund scallop and geoduck larvae; whether bivalve prey may be a source of disease exposure for sea stars is currently unknown.

The first photograph in the below series of a sea star with wasting disease was taken on June 27^th, 2014 on Guemes Island, Washington. The second 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

Early symptoms of SSWD can include lethargy and a deflated appearance. Sick stars can then develop lesions that appear in the ectoderm followed by tissue decay and eventual fragmentation of the body and death. All of these symptoms can arise in healthy sea stars that are subjected to other, non-disease types of stressors, such as being stranded too high in the intertidal zone (for example). “True” wasting disease will be present in individuals that are found in suitable habitat, often in the midst of other affected individuals. 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 current outbreak of SSWD 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, in collaboration with community science groups, have since documented wasting in sea stars from Alaska through California (see sea star map for specific locations). Die-offs were most severe between 2013-2014, but regional flare-ups of SSWD continue to be observed.

Photo credits: Mark Nayer (left), Nate Fletcher (center), Michael Kyte (right).

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 (Evasterias troschelii), ochre star (Pisaster ochraceus) and sun star (Solaster), leather star (Dermasterias imbricata), vermilion star (Mediaster aequalis), six-armed stars (Leptasterias), and bat star (Patiria miniata). We don’t know whether the disease spreads sequentially from one species to the next, or if some species simply take longer to express symptoms. 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 see our Updates about Sea Star Wasting Disease.

Tracking and Documenting Observations

SUBMIT OBSERVATIONS HERE

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. In addition to sea star disease observations, observations of disease in the purple sea urchin (Strongylocentrotus purpuratus) can be reported (as of December, 2014). Note that prior to December 2014, there are no observations for S. purpuratus on the map. For urchin species other than S. purpuratus observations should be recorded in the ‘Additional Information’ section. Please direct questions to Melissa Miner, Rani Gaddam, and Melissa Douglas (seastarwasting@googlegroups.com).

Our research group is concentrating on:

Documenting the distribution and health of sea stars along the west coast of North America by means of reports submitted by the general public, collaborative monitoring done by community science groups, and our own sampling as part of MARINe Long-Term Monitoring.
Assessing the direct impact of SSWD on intertidal sea star populations, and the outlook for recovery.
Assessing how the severe decline of sea stars impacts the distribution and abundance of other species in the rocky intertidal community, and how these impacts might vary by location.

Other research groups are addressing the pathology and infectiousness of wasting. These groups include Cornell (Harvell & Hewson), University of Rhode Island (Gomez) and Brown University (Wessel).

If you are interested in adding information to our Sea Star Map, please see the options below.

Fill out the Sea Star Disease Observation Log

Please submit observations through our web form. If you have any photos or spreadsheets to send, please send them to seastarwasting@googlegroups.com.

Please continue to submit observations after spending time diving or exploring the intertidal. We regularly update our website with the latest reports, as well as the Sea Star Map. Please remember to fill out a log even if you search and only find healthy sea stars! This information is just as valuable as observations of diseased individuals.

Identification guides (PDF)

Pisaster ochraceus symptoms guide

Juvenile sea star identification

Evasterias symptoms guide

Examples of Mild vs. Severe symptoms

Urchin disease guide

(note: Disease in urchins is likely different from SSWD)

Collect additional sea star data:

Please see the downloadable PDFs below if interested in long-term monitoring protocols. If you are interested in collecting additional information about sea star counts, sizes, and disease categories, please contact Melissa Miner, Rani Gaddam, and Melissa Douglas (seastarwasting@googlegroups.com) 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.