Sea Star Wasting Syndrome

Sea Star Wasting Syndrome

September 21, 2015

Excerpts from

Sea Star Wasting Disease

“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.

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 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.Sea Star Wasting Disease

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.”

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Last revised 15-Sep-15