Abstract

Asteroidea mortality in several genera was unusually high along the west coast of North America, from Alaska to southern California from September 2013–February 2014. The number of dead sea stars is estimated in the millions and the mortality rates in affected regions continue to be high with 100% mortality documented in certain sea star species. A similar but smaller event occurred along the east coast of the United States earlier in 2013. An international, multidisciplinary team of investigators at various institutions are participating in the ongoing efforts to determine the cause of this unusual wildlife mortality event. Concurrent to mortality of free-ranging animals, sea stars at several aquariums also began to die. Species that have been highly affected include Pycnopodia helianthoides, Pisaster spp. and Evasterias spp., while sympatric species such as Asterina spp., Dermasterias spp., and Mediaster spp. have been affected to a much lesser degree. In British Columbia and Washington, outbreaks affecting Pycnopodia sp. were first reported in northern Washington and inner British Columbia waterways while outer-coast sea stars were not immediately affected. No obvious water-quality factors have been associated with disease outbreaks. Clinical signs include a melting syndrome that begins as epidermal ulcerations at the junction of the disc and arms that can progress to transmural perforation with extrusion of digestive organs resulting in complete dissolution of the sea star in 24 to 72 hours leaving only ossicles. Other animals may show progressive autotomy of the limbs with death in 24 to 48 hours. Cytology from affected animals has shown various bacteria including long, motile forms. Histologic examination identified degeneration, necrosis and ulceration of the epidermis and cuticle with inflammation (characterized by edema and infiltration of coelomocytes) extending through the body wall and into the coelom. Despite the clinical suspicion of an infectious agent and early transmission studies suggesting that a pathogen can be spread from affected to non-affected animals, no obvious pathogen has been identified by traditional diagnostic techniques. This has necessitated the use of highly sophisticated and technologically advanced methods to help characterize possible etiologies.

Acknowledgements

We cannot begin to list the numerous individuals and institutions including citizen science groups, divers, volunteers, as well as government, private, and non-governmental organizations that have been involved in the investigation of this outbreak. We would like to recognize Donna Gibbs, Neil Fisher, Jessica Shultz, Kate Cooper, Sion Cahoon, Bryan Kent, Danny Kent, Stefania Gorgopa, and Justin Lisaingo of the Vancouver Aquarium for their amazing assistance with sample collection and providing data. Special thanks to Dr. Sal Frasca for comments and assistance with histopathology and electron microscopy.

* Presenting author