Effects of wasting disease on sea star populations in southern California: Variations over a 40-year period

Sea star wasting disease has been described for asteroid populations from many parts of the world and for numerous species. The causative agents are generally unknown. However, within the Southern California Bight, a Vibrio bacterium appears to have been the cause of wasting disease in the 1980s, and probably the 1990s, during warm water episodes associated with El Ninos. Although a densovirus was implicated in the mass mortality of one species of subtidal sea star during the geographically widespread epizootics that began in 2013, the etiology appears to vary among species, locations, and time periods, and in some cases may not even be associated with a pathogen. We have been studying subtidal benthic communities in southern California since the 1970s and have documented the population effects of wasting disease epizootics associated with warm water El Nino events from 1980 through 2020. Until 2015, population declines coincident with wasting disease were followed by various degrees of recovery, whereas after 2015 there has been little or no recovery at our study sites. Prior to 2013, wasting disease in the northeast Pacific was only reported from locations in the Gulf of California, the southern California bight, and the coast of Vancouver Island, British Columbia. Since 2013, epizootics of wasting disease among sea stars have been observed along the entire west coast of North America. We speculate that the lack of recovery after 2015 may be due to a reduction in larval supply caused by the greater geographical extent of the disease.