The outbreak of sea star wasting syndrome began in 2013 and is one of the most extensive marine epizootics on record.
At least 20 species have been affected, with many species experiencing extremely high mortality. The disease remains active and it is unknown if further outbreaks will occur. When animals are infected, lesions develop that can progress into arm detachment, grip loss, “melting” and death. This process is rapid; sea stars can go from visually asymptomatic to dead within days, and few recover once symptoms are observed. Above photo: Multiple mottled sea stars (Evasterias troscheli) losing arms and their grip as they succumb to sea star wasting syndrome in 2014 at Coupeville Wharf, Whidbey Island, Washington. Photo by Jan Kocian.
The cause is not well understood. We are just beginning to understand the infectious agent and the susceptibility of the affected sea stars. There is evidence that sea star associated densovirus (SSaDV) or wasting asteroid-associated densoviruses (WAaDs) cause the syndrome, but there may be multiple causes. Warmer temperatures exacerbate the disease symptoms and progression, but there is not definitive evidence that the outbreak was caused by climate change. Photo right: Lesions on an infected giant pink sea star (Pisaster brevispinus) in 2014, Langley, Whidbey Island, Washington. Photo by Jan Kocian.
The potential for natural recovery varies widely among species. Observations of the formerly common sunflower star Pycnopodia helianthoides have been sparse or non-existent throughout much of the US West Coast since the outbreak, which is of serious concern. Though observations are limited, the giant pink sea star Pisaster brevispinus recovery has not been observed in bays and estuaries of Oregon. Conversely, a large number of juvenile ochre stars Pisaster ochraceus have been observed at many sites in Washington, Oregon and northern and central California, though almost no recruitment has been observed in southern California. Photo right: A very young ochre sea star (Pisaster ochraceus) that was part of a large recruitment pulse in 2016, after the outbreak. Cape Perpetua Marine Reserve, Oregon. Photo by Jonathan Robinson.
One severely affected species was the ochre star Pisaster ochraceus, which serves as a keystone predator in the intertidal zone. By consuming the competitively dominant mussels Pisaster opens space for other species and increases biodiversity of primary space holders. Since the outbreak, mussels and other prey species have increased drastically in some places. Photo right: A mussel bed showing distinct zonation with coverage of diverse algae and invertebrates below near Santa Barbara, California. Photo by May Roberts.
The sunflower star Pycnopodia helianthoides was nearly extinguished and is now rare. Since sunflowers stars eat sea urchins that eat kelp, sunflower stars are an important part of healthy kelp forests. The absence of sunflower stars is hindering the recovery of kelps after kelps suffered after El Niño and the warm water "blob" in the North Pacific in recent years. This is important for the many species that depend on kelp forests.
We need your observations!
We rely on reports by beachcombers to tell us how sea star populations are doing. Please submit your observations of healthy and wasting sea stars to seastarwasting.org. We are especially interested in your reports of the sunflower star Pycnopodia helianthoides and any young sea stars. Photo right: Sunflower stars with severe wasting syndrome in 2014 on Whidbey Island. Photo by Jan Kocian.