Increased Water Temperature Potentiates Sea Star Wasting Disease Mortality in the Ochre Star (Pisaster ochraceus).

Beginning in the late spring-early summer of 2013 a series of mass mortality events produced by an unidentified infectious agent ravaged sea star populations on the Pacific coast, leading to extirpation of multiple populations in some areas. The causative agent for this outbreak has since been tenuously identified as a Sea Star-associated Densovirus (SSaDV). However, SSaDV has been detected in archival specimens over 70 years old and viral gene expression has been detected in asymptomatic specimens of the Ochre Star (Pisaster ochraceus). In beginning to untangle contributing factors to the current mortality events, we conducted controlled laboratory experiments with infected P. ochraceus and Mottled Stars (Evasterias troschelii) collected from near Birch Bay State Park in Blaine, WA. Individuals were housed in 38L tanks with water temperatures maintained at 9.0 degreesC or 12.0 degreesC and monitored for Sea Star Wasting Disease (SSWD) progression and mortality for approximately 2 months. Individuals housed at 9.0 degreesC showed reduced symptom progression and increased survival compared to individuals housed at 12.0 degreesC. Some healing and recovery was observed in 9.0 degreesC but not 12.0 degreesC housed individuals. Our data bears implications for the impact of climate change and ocean warming on intertidal populations of invertebrate keystone predators on the Pacific Coast.