A doubled down invasion of the northeast Pacific by the Asian mud shrimp, Upogebia major and its coevolved bopyrid isopod parasite, Orthione griffenis

Dramatic declines of the native northeast Pacific mud shrimp, Upogebia pugettensis over the last three decades have occurred in response to intense infestations by the Asian bopyrid isopod parasite, Orthione griffenis, that was introduced in the 1980s. We report herein the arrival of the Asian mud shrimp, Upogebia major, in San Francisco Bay no later than 2006. Complications of identifying juvenile U. major and inefficiencies of collecting mature and readily identified specimens recovered by conventional sampling devices are likely to have delayed its identification and discovery. U. major is less vulnerable to O. griffenis and is displacing or replacing U. pugettensis in its present 200 km range to the north and south of San Francisco Bay. Upogebia major, as a coevolved alternative host, assures persistence of O. griffenis in this region even where native species extinctions occur and can potentially expand to all habitats that are presently invaded by O. griffenis (Alaska to Baja California Norte). The individual and combined O. griffenis and U. major invasions thus threaten U. pugettensis in particular and all other native Upogebia species occurring north of Mexico. Our review of Upogebia taxonomy for a key to species revealed a previously reported 1912 invasion of San Francisco Bay by Upogebia affinis that was in error; hence, the introduction of U. major is the first confirmed gebiid invasion in the world. Greater resolution of U. major natural history and timing of its invasion is needed to test whether it evaded present vector management efforts. Intervention is warranted to limit the doubled down U. major and O. griffenis invasion and to conserve U. pugettensis and other native Upogebia species from ecological or absolute extinction in the coming decades.