A disease that afflicts sea stars has taken root in Pacific waters from Alaska down to California, including portions of Redwood National and State Parks. Biologists say this year's mass mortality tied to the disease is "unprecedented."

While the cause of "sea star wasting syndrome" hasn't been pinned down, biologists believe it has to do with ocean waters that are warmer than normal. Park officials note that in the past, "bacterial and viral agents and environmental toxins and contaminants were suspected but not confirmed. While the ultimate cause is not clear, sea star wasting events are often associated with warmer than typical water temperatures, as was the case for the major die off in southern California in 1983-1984 and again (on a lesser scale) in 1997-98."

Sea star wasting syndrome is occurring along much of the Pacific coast of North America from Alaska to California, including Redwood National and State Parks. While this is not the first time that sea star wasting syndrome has been observed, the mass mortality of this epidemic is unprecedented, notes a park release.

“Although similar sea star wasting events have occurred previously, a mortality event of this magnitude, with such broad geographic reach has never before been documented,” reports the website for the Department of Ecology and Evolutionary Biology at the University of California at Santa Cruz. “Early signs of the syndrome can include a ‘deflated’ appearance, unnatural twisting, or small lesions on the surface that may increase in size and number. Wasting syndrome can progress rapidly, and often leads to loss of arms, softening of tissue, and eventual death just a few days after external signs become visible.”

Redwood National and State Parks researchers have monitored park intertidal zones twice a year since 2004. While the syndrome began to be noted at multiple sites along the West Coast in late spring last year, nothing abnormal was observed at park study areas during a survey in May 2013. One year later, sea wasting syndrome is in the parks.

A park release says ochre sea stars with small lesions were found at the three rocky intertidal sites (False Klamath Cove, Damnation, and Enderts) last December. On February 21, Yurok tribal technicians found large numbers of dead ochre sea stars on park beaches along the mouth of Wilson Creek at False Klamath Cove. Three days later, park employees documented the die off and surveyed the intertidal rocky area adjacent to Wilson Creek.

Live ochre stars with symptoms of the wasting syndrome—missing legs, lesions, and deteriorating tissue—were found, but also healthy looking sea stars.

All park intertidal study sites will be sampled again in May with the park’s UC Santa Cruz partners.

Scientists do not know what is causing sea star wasting syndrome, but are working to understand the causes and the consequences of the event. One challenge is that the cause may be different in different regions. The UC Santa Cruz Department of Ecology and Evolutionary Biology is taking a lead role in collecting and analyzing monitoring data from agencies and organizations, including the National Park Service, all along the West Coast. Other research groups at Cornell, University of Rhode Island, Brown, Western Washington University and Seattle Aquarium are addressing the pathology and infectiousness of wasting.

Scientists hope they can come to better understand this disease because a large-scale, mass mortality of individual marine species can result in dramatic ecosystem-wide changes with long-term impacts.

Two sea star species affected most are purple sea star, or ochre, starfish (Pisaster ochraceus) in the intertidal and sunflower sea star (Pycnopodia helianthoides) in the subtidal zone. Ecologists consider sunflower and ochre stars to be “keystone species” because they have a disproportionately large influence on the distribution and abundance of many other species. Scientists anticipate that such a large mortality event in keystone species could change the intertidal and subtidal seascapes.

For example, the keystone species Pisaster ochraceus is considered a top predator in the rocky intertidal zone, as its diet includes mussels, barnacles, snails, limpets, and mollusks. If removed, the mussel population has the potential to dramatically increase, which could significantly alter rocky intertidal community structure.

The wasting syndrome underscores the value of long-term scientific monitoring, and also illustrates the importance of interagency partnership and cooperation and of the park’s being a partner in the Multi Agency Rocky Intertidal Network (MARINe). Other local groups, such as the Yurok Tribe, are also concerned about what can be done to prevent the spread.