Sea star wasting disease (SSWD) in central California
- Pete Raimondi
University of California, Santa Cruz
- Mark Carr
University of California, Santa Cruz
- Fiorenza Micheli
- Steve Lonhart
Monterey Bay National Marine Sanctuary
Sea stars along much of the Pacific coast of North America are experiencing a mass mortality event (MME) called sea star wasting syndrome (hereafter SSWD). Multiple species of sea stars have been impacted, both in the intertidal and adjacent nearshore subtidal, including kelp forests.
Early signs of SSWD can include a deflated appearance, unnatural twisting, or small white lesions on the surface that may increase in size and number. SSWD can progress rapidly (10 days), and often leads to loss of arms, softening of tissue, and eventual death just a few days after external signs become visible. Although similar sea star MMEs have occurred previously, the geographic magnitude (from Alaska to Mexico) has never before been documented.
Extensive samples have been collected to identify the causative agent and the conditions that may have caused the start of the outbreak. Pathology samples were evaluated by a working group of veterinary pathologists from Cornell University, Wildlife Conservation Society, Northwest ZooPath, Roger Williams University, University of California Davis, University of Connecticut and the US Geological Survey to define the disease process and help determine the underlying cause. Funding from NSF and WA Sea Grant is also supporting infectiousness experiments at Western Washington University.
A paper by Hewson et al. (2014) published in the Proceedings of the National Academy of Sciences (Nov 17, 2014) titled "Densovirus associated with sea-star wasting disease and mass mortality" that links the virus to the recent MMEs.
Previous MMEs among echinoderms (i.e. stars, urchins, and relatives) have taken place in the past, most recently associated with El Nino events and primarily limited to southern CA (1983-84 and 1997-98). SSWD progresses rapidly, killing stars within days, and has lead to the near absence of some species (e.g., sunflower star Pycnopodia helianthoides). Previous studies on similar MMEs have described either a bacterium (vibrio) or virus as the causative agent.
Staff divers from MBNMS are assisting UCSC divers with surveys for signs of SSWS at sites in Monterey Bay, Carmel Bay, and parts of Big Sur. The West Coast Regional office provided 5 days-at-sea in spring 2014 aboard to the RV 4107, a 41 ft NOAA small boat that supports diving operations for up to six divers.
Summary to DateUpdate October 2014:
Since the fall of 2013, the MARINe Research Group at UC Santa Cruz (seastarwasting.org) has been able to track the occurrence of Sea Star Wasting Disease (SSWD) along the west coast of North America largely due to observations and monitoring by concerned individuals. While we continue to monitor the occurrence of SSWD and encourage you to continue to submit your observations, we are also beginning to investigate the possible ecological consequences of SSWD. SSWD has the potential to significantly change the communities in which sea stars live because they play a key role in their habitats; sea stars are generally not prey for other species, and as important predators, their prey may become more abundant through reduced mortality.
In order to understand the possible consequences of SSWD, we need to determine the potential for replenishment of sea stars in affected areas. Key to this will be observations and monitoring of juvenile sea stars. Since the winter of 2013 and spring of 2014, we have seen very high abundances of juveniles in some of our hardest-hit sites, and would like to document the abundance and health of newly recruited sea stars on a large spatial scale. This will only be possible through the help of observers along the entire west coast. We encourage you to view our Juvenile Sea Star Identification Guide as identifying small sea stars is trickier than large ones (submitting photos is highly encouraged). We also encourage you to submit observations of juvenile sea stars through our new Juvenile Sea Star Observation Log. More information is available at the following link:
Thank you for your interest and help,
The MARINe Research Group at UC Santa Cruz (seastarwasting.org)
Initial Emergence and Patterns for 2013
SSWS was first noted in ochre stars (Pisaster ochraceus) in June 2013 along the Washington coast during monitoring surveys conducted by researchers from Olympic National Park. ONP is part of a west coast-wide, long-term monitoring effort--the Multi-Agency Rocky Intertidal Network (MARINe)--thus researchers from Alaska to California were quickly alerted to the emergence of SSWD. Indeed, the majority of SSWD-related observations are for ochre stars (the most common sea star in the intertidal). Other intertidal species affected include Evasterias troschelii, Dermasterias imbricata (leather star), and Leptasterias spp. (six-armed star). As of December 2013, signs of wasting had been observed at 45 of 84 MARINe sites sampled since summer 2013, spanning the entire coast from Alaska to San Diego but varying in intensity from low levels of infection to mass mortality. Large gaps in available information hinder efforts to understand the outbreak.
In August 2013, divers reported a MME of the sunflower star, Pycnopodia helianthoides, just north of Vancouver, British Columbia and shortly thereafter, other sea star species in the region began showing signs of wasting. During October/November 2013, a similar MME was documented in Monterey, CA, beginning with sunflower stars, then spreading to other species within days to weeks. As of mid-December, substantial numbers of sea stars with SSWS were reported from southern California. Subtidal observations have thus far been largely opportunistic, and highly regional. Efforts are underway to standardize and coordinate a sampling approach, to better document the distribution of wasting syndrome in the subtidal and identify patterns of spread.
In nearly all subtidal wasting events documented during 2013, the sunflower star is the first species to succumb to the disease. Other species affected (listed roughly in order of when signs of wasting first appear) include: Orthasterias koehleri (northern rainbow star), Pisaster brevispinus (short-spines star), Pisaster giganteus (giant-spines star), Evasterias troschelii (False ochre star), Pisaster ochraceus (ochre star), Solaster spp. (sun star), Dermasterias imbricata (leather star), Mediaster aequalis (vermilion star), Leptasterias spp. (six-armed star), and Patiria miniata (bat star). It is unknown whether the disease spreads sequentially from one species to the next or if some species simply take longer to express symptoms. Two species for which massive, geographically expansive (but patchy) declines have been well documented are the sunflower and ochre stars. Other species are less abundant, and thus impacts of wasting syndrome are less clear.
- UPDATE February 2015:
Research divers conducting subtidal surveys in Monterey Bay kelp forests have noted a small number of bat stars with minor lesions, and even fewer dissolving. The number of diseased bat stars encountered in February 2015 was likely less than 5%. Adult giant-spined stars (Pisaster giganteus) were apparently healthy, although several were seen 'twisting' their rays (<10%).
April 2014: From October 2013 to March 2014 the incidence of SSWD among bat stars (Patiria miniata, formerly Asterina) was very low. However, observations of multiple bat stars with signs of SSWD were reported in April 2014 at the Monterey breakwater and Lover's Point in Pacific Grove.
- Symptoms of SSWD have been observed from Alaska to Mexico.
- Onset of SSWD is rapid, causing declines in sunflower stars, then ochre and giant-spines stars, as well as less common stars such as the northern rainbow star. Within weeks the populations have been severely depleted.
- Stars surviving the initial infection phase appear to remain healthy, albeit at low numbers. Juvenile and recently recruited sunflower stars are found at many of the sites where adults are absent.
DiscussionOngoing Research Field surveys are being done by MARINe groups at long-term, intertidal monitoring sites along the entire west coast. Counts and size distributions of different sea star species in permanent plots can be compared to historic data, reaching back 30 years in some cases. Rapid funding from NSF, the CA Ocean Science Trust, the Packard Foundation and, OR & WA Sea Grant is supporting additional surveys to target under-represented areas of the coast (coordinated by UC Santa Cruz and Western Washington University). MARINe members will be assisting numerous citizen science groups in WA, OR and CA to establish sites where sea star populations will be monitored for impacts of wasting syndrome. Divers and other citizens wishing to contribute observations can either join the MARINe effort or tweet in simpler observations of sick and healthy stars to www.sickstarfish.com or inaturalist.org/projects/pisaster-disaster-tracking-starfish-wasting-disease. It is very important to capture the timing of new disease clusters, since so little is known about the rate and patterns of disease spread in the ocean. Detailed data will allow testing of hypotheses about potential causes.
MARINe has developed a tracking log that can be downloaded from the seastarwasting.org website, which can be used by researchers and the general public to record observations of wasting syndrome.
Observations from field surveys and tracking logs are uploaded to the MARINe sea star wasting Tracking Map, which includes species-specific information about wasting syndrome presence/absence, and dates when sites were visited (supported by funding from Bureau of Ocean Energy Management, Packard Foundation, and Moore Foundation). http://data.piscoweb.org/marine1/seastardisease.html
- Size structure
Study MethodsThere are multiple methods being used to characterize the spatial extent of sea stars affected by the disease and to quantify sea star densities, size structure, and level of infection.
Quantitative Density methods:
The Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) at UC Santa Cruz and collaborating partners at Monterey Bay National Marine Sanctuary, are collecting density data for sea stars at sites surveyed on an annual basis in the summer. Current efforts are underway to survey these same sites between the planned annual surveys.
During annual PISCO surveys, a site consists of three depth zones (20, 12.5, and 5 m) with two belt transects in each depth. A 30 m tape is used to follow the depth contour and parallel to shore, and an area 2 m wide by 30 m long is surveyed for sea stars.
Each star is sized (5 cm categories based on greatest ray length), identified to species, and health status assessed (i.e. healthy, mild signs of disease, or diseased).
Counts of Fixed Sampling Areas
Sampling the same exact (i.e. fixed) area repeatedly can also be accomplished by counting all sea stars on permanent underwater features, such as distinct rock outcroppings surrounded by sand, submerged docks, or harbor jetties (or well defined sub-sections of jetties). The key to this method is defining an area that can be counted completely during each survey. For example, it may not be possible to count all sea stars along the entire length of a jetty, but small, well defined/described subsections could be accurately and completely counted during repeated surveys.
Roving transects repeated within Defined Sampling Areas
For sites where permanent underwater features cannot be used as transect start/end markers, or well-defined underwater features do not exist, sea stars can be counted along non-permanent (i.e. random) transects within a defined sampling area. The boundaries of the sampling are should be defined by GPS coordinates, which can be accomplished using a boat’s GPS system, a handheld GPS, or Google Earth. Within these defined sampling area boundaries, divers can swim random, non-overlapping transects at a consistent depth or along a depth profile for a set amount of time (e.g., swim 10 min along compass heading, then shift over 5 m and return along the opposite compass bearing). The goal is to try to cover approximately the same area during all subsequent surveys within the defined sampling area.
Figures and Images
Figure 1. Sea star syndrome (S3) is a wasting disease that has caused a mass mortality event (MME) among several sea star species. This giant-spined star is showing symptoms of S3, twisting its rays. In some cases, it appears stars tear off their own rays.
Figure 2. This giant-spined star (Pisaster giantess) is starting to decay, and it appears an orange bat star is moving into feed on the necrotic tissue.
Figure 3. Map of sites that have been surveyed for signs of S3 (as of February 26, 2014). Red markers indicate S3 is present while blue markers indicate it has not bee detected yet. For the latest info, go to: http://data.piscoweb.org/marine1/seastardisease.html